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Loss processes affecting submicrometre particles in a house heavily affected by road traffic emissions
Abstract
The fraction of outdoor aerosol that penetrates into indoor environments plays an important role in determining the contribution of outdoor particles to the total lung dose of particles in human exposure. The objective of this study was to investigate the physical processes affecting migration of outdoor traffic particles into indoor environments. Particle number size distributions were measured by a fast mobility particle sizer system in both indoor and outdoor environments of a house located in close proximity to a busy street in Bologna (Italy) in the period February–April 2012. Indoor to outdoor (I/O) ratios for submicron particle number concentrations showed strong dependence on particle size and meteorological conditions. The loss rates of particles due to deposition, coagulation, and evaporation were determined using dynamic mass balance and coagulation models. Higher loss rates were found for small particles (nucleation and Aitken mode) indoors than for larger particles (accumulation mode). The coagulation and evaporation processes made a significant contribution to the loss of traffic nanoparticles indoors, especially during the day time. Application of positive matrix factorization to the indoor and outdoor particle size distributions showed a substantial loss of traffic-generated nucleation mode particles in the indoor environment, with evaporation playing a major role.
Copyright © 2017 American Association for Aerosol Research
... Besides, the indoor particle concentration is also determined by the deposition, coagulation and resuspension of particles. Assuming that air is well mixed indoors and the ambient concentration is steady, and the mass balance equation for particles can be expressed as (Rim et al. 2016;Thatcher and Layton 1995;Vu et al. 2017): ...
... (9) with the measured air change rate and the estimated deposition rate referring to previous studies. Vu et al. (2017) evaluated the penetration factor as the ratio of as the ratio of the downstream to upstream concentration through the mechanical ventilation system. Peng et al. (2020) developed a method based on indoor PM 2.5 removal by an air cleaner as Eq. ...
... 0.72-1, and 0.69-0.86, respectively (Koutrakis et al. 1992;Ozkaynak et al. 1996;Tung et al. 1999;Williams et al. 2003;Zhao and Stephens 2017), which is consistent with the sizedependent results presented in Figs. 1 and 2. The size-dependent measured results in residences (A) and other real buildings (B) are presented in Fig. 1 (Chao et al. 2003;Chatoutsidou et al. 2015;Chen et al. 2020b;Hussein et al. 2006;Long et al. 2001;Maskova et al. 2016;Rim et al. 2010Rim et al. , 2013Thatcher et al. 2003;Tran et al. 2017;Vette et al. 2001;Vu et al. 2017;Xie et al. 2020;Zhao and Stephens 2017;Zhou et al. 2019;Zhu et al. 2005). The penetration factors are 0.78 AE 0.17 for accumulation-mode particles (0.1-1 μm diameter). ...
... Besides, the indoor particle concentration is also determined by the deposition, coagulation and resuspension of particles. Assuming that air is well mixed indoors and the ambient concentration is steady, and the mass balance equation for particles can be expressed as (Rim et al. 2016;Thatcher and Layton 1995;Vu et al. 2017): ...
... (9) with the measured air change rate and the estimated deposition rate referring to previous studies. Vu et al. (2017) evaluated the penetration factor as the ratio of as the ratio of the downstream to upstream concentration through the mechanical ventilation system. Peng et al. (2020) developed a method based on indoor PM 2.5 removal by an air cleaner as Eq. ...
... 0.72-1, and 0.69-0.86, respectively (Koutrakis et al. 1992;Ozkaynak et al. 1996;Tung et al. 1999;Williams et al. 2003;Zhao and Stephens 2017), which is consistent with the sizedependent results presented in Figs. 1 and 2. The size-dependent measured results in residences (A) and other real buildings (B) are presented in Fig. 1 (Chao et al. 2003; Chatoutsidou et al. 2015;Chen et al. 2020b;Hussein et al. 2006;Long et al. 2001;Maskova et al. 2016;Rim et al. 2010Rim et al. , 2013Thatcher et al. 2003;Tran et al. 2017;Vette et al. 2001;Vu et al. 2017;Xie et al. 2020;Zhao and Stephens 2017;Zhou et al. 2019;Zhu et al. 2005). The penetration factors are 0.78 AE 0.17 for accumulation-mode particles (0.1-1 μm diameter). ...
Even people mostly stay indoors, they are constantly exposed to outdoororiginated
particles. Outdoor particles can penetrate into indoor environments
via the building envelope through ventilation and air infiltration. Penetration
factor is the ratio of outdoor particles entering the indoor environments through
the building’s envelope, and infiltration factor is the equilibrium fraction of
ambient particles that enter and remain suspended indoors. The penetration factor
and infiltration factor are important parameters to understand the transport of
particles from outdoors to indoors. Penetration factors can be measured according
to regression approach, equilibrium concentration approach, or error analysis approach. The penetration factors are 0.78 � 0.17 for accumulation-mode particles
(0.1–1 μm diameter). They decreased due to Brownian diffusion for smaller
particles, or due to stronger gravitational setting and impaction for larger particles.
In addition to particle sizes, penetration factors are determined by pressure
differences, geometry and surface roughness of cracks, etc. Infiltration factors can
be measured by regression approach, equilibrium concentration approach, or
tracer element approach, and can also be simulated based on the air change
rate, penetration factor and deposition rate. The infiltration factors of PM2.5 are
approximately 0.50, which are lower than ultrafine particles and higher than PM10
under the same conditions. Infiltration factors are also influenced by air change
rates, window opening behaviors, ventilation systems, etc.
... However, few studies have discussed the effects of coagulation on the F inf of UFPs. Franck et al. (2003) found that a higher ratio of indoor to outdoor UFP concentrations without indoor sources tend to correlate with lower outdoor concentrations, and Vu et al. (2017) estimated that the coagulation of indoor UFPs was approximately 11% compared of the deposition effect in an Italian residence without indoor sources. Despite the fact that outdoor UFP concentrations are higher in China than in developed countries (Gao et al., 2007;Hussein et al., 2004;Stanier et al., 2004;Wang et al., 2013;Wehner and Wiedensohler, 2003;Wu et al., 2008;Xu et al., 2011;Zhang et al., 2016Zhang et al., , 2017, the impact of the coagulation on F inf of UFPs remains unclear in the Chinese context. ...
... where C in,os is the indoor UFP concentration originating from outdoor sources [#/cm 3 ], and C out is the outdoor UFP concentration [#/cm 3 ]. The mass balance equation for indoor UFPs can be expressed as (Vu et al., 2017): ...
... k coag ¼ À P dp " 1 2 P n P m K m;n C in;m C in;n À C in;dp P n K dp;n C in;n (Vu et al., 2017), C in,m , C in,n and C in,dp are the indoor concentrations of particles in size bin m, n and d p , respectively [#/cm 3 ], and K m,n and K dp,n are the coagulation coefficients between particles in bins m and n, d p and n, respectively [cm 3 /h]. The numerator of Eq. (3) represents the net loss of indoor UFP concentration due to coagulation, which depends on the generation of particles with diameter d p [nm], when particles in size bin m coagulate with particles in size bin n, and the reduction of the concentration of particles with diameter d p , when they coagulate with particles in all other size categories. ...
Ambient ultrafine particles (UFPs: particles of diameter less than 100 nm) cause significant adverse health effects. As people spend most time indoors, the outdoor-to-indoor transport of UFPs plays a critical role in the accuracy of personal exposure assessments. Herein, a strategy was proposed to measure and analyze the infiltration factor (Finf) of UFPs, an important parameter quantifying the fraction of ambient air pollutants that travel inside and remain suspended indoors. Ninety-three measurements were conducted in 11 residential rooms in all seasons in Beijing, China, to investigate Finf of UFPs and its associated influencing factors. A multilevel regression model incorporating eight possible factors that influence infiltration was developed to predict Finf and FinfSOA (defined as the ratio of indoor to outdoor UFP concentrations without indoor sources, but with indoor secondary organic aerosol (SOA) formation). It was found that the air change rate was the most important factor and coagulation was considerable, while the influence of SOA formation was much smaller than that of other factors. Our regression model accurately predicted daily-average Finf. The annually-averaged Finf of UFPs was 0.66 ± 0.10, which is higher than that of PM2.5 and PM10, demonstrating the importance of controlling indoor UFPs of outdoor origin.
... It was connected to a switching valve to measure both indoor and outdoor size distributions every 10 min, and a constant air exchange rate of 0.5 h −1 was controlled by a novel mechanical system. The details of the sampling campaign were described in our previous work (Vu et al. 2017;Zauli Sajani et al. 2015). An hourly dataset of NO, NO 2 and NO x and daily PM 2.5 and PM 10 were collected at the Porta San Felice monitoring site (longitude 11.329, latitude 44.500) which is located in the urban traffic area and close to our traffic-influenced sampling site. ...
... The hourly doses of indoor aerosols in the whole lung by number, surface area and mass were 2.5 × 10 9 particles/h, 48.2 mm 2 /h and 0.91 μg/h which are less than those of outdoor aerosols by 4.1, 2.7 and 2.1 times. When aerosols enter into a house, their concentrations decline due to evaporation and deposition processes (Vu et al. 2017). Higher loss rates of Figure 6 shows the diurnal variation of hourly lung dose of both outdoor and indoor aerosols in the human respiratory tract. ...
Estimates of lung dose of submicron particles in the human respiratory system play an essential role in assessing health outcomes of aerosol exposure. The objectives of this study are to calculate the regional lung dose of traffic-generated particles by different metrics from exposure in outdoor and indoor environments and to identify main factors determining the lung dose. Particle number size distributions were collected in both indoor and outdoor environments in two unoccupied apartments from 22nd February to 30th April 2012 in Bologna, Italy. The whole lung doses of outdoor aerosols by number, surface area and mass at a traffic site were 1.0 × 10¹⁰ particles/h, 130 mm²/h and 1.9 μg/h, respectively. A majority of particles by number and surface area were found to deposit in the alveolar region (65%). The physical properties of particles such as shape, hygroscopicity and density play an important role in the calculation of surface area and mass dose due to shifting of the lung deposition curve. Particle number can predict well the regional dose by number, while PM2.5 and PM10 are good metrics for the prediction of surface area and mass dose. Good correlations between NOx and the surface areas and mass dose (r² ~ 0.8) and number dose (r² ~ 0.7) of submicron aerosols suggest that NOx may be a good indicator for predicting the health outcomes of traffic-generated aerosols. The doses of indoor sub-micrometre aerosols are less than those of outdoor aerosols by factors of 4.1 (for number), 2.7 (for surface area) and 2.1 (for mass). Due to traffic emissions, the lung dose of outdoor aerosols in the traffic area was much higher than that in the residential area by 5 times for number and surface area and 2 times for mass. A different exercise level (standing, walking, running and cycling) has only a slight influence on the whole lung deposition fraction of submicron aerosols but has a large effect on the dose due to differences in ventilation rate.
... In their study, indoor PM 2.5 was seen to come from outdoor sources in the main, although indoor sources also were found to be a noticeable contributory factor [57]. studied the factors affecting penetration and infiltration of nanoparticles (i.e. UFP) from outdoor origin indoors and found that coagulation and evaporation processes were significant processed contributing to the loss of traffic nanoparticles indoors [58]. The results of Vu's study are consistent with the current results for UFP showing a smaller contribution from outdoor traffic to personal exposure than from indoor sources. ...
Purpose
Indoor and outdoor factors affect personal exposure to air pollutants. Type of cooking appliance (i.e. gas, electricity), and residential location related to traffic are such factors. This research aims to investigate the effect of cooking with gas and electric appliances, as an indoor source of aerosols, and residential traffic as outdoor sources, on personal exposures to particulate matter with an aerodynamic diameter lower than 2.5 μm (PM 2.5 ), black carbon (BC), and ultrafine particles (UFP).
Methods
Forty subjects were sampled for four consecutive days measuring personal exposures to three aerosol pollutants, namely PM 2.5 , BC, and UFP, which were measured using personal sensors. Subjects were equally distributed into four categories according to the use of gas or electric stoves for cooking, and to residential traffic (i.e. houses located near or away from busy roads).
Results/conclusion
Cooking was identified as an indoor activity affecting exposure to aerosols, with mean concentrations during cooking ranging 24.7–50.0 μg/m ³ (PM 2.5 ), 1.8–4.9 μg/m ³ (BC), and 1.4 × 10 ⁴ –4.1 × 10 ⁴ particles/cm ³ (UFP). This study also suggest that traffic is a dominant source of exposure to BC, since people living near busy roads are exposed to higher BC concentrations than those living further away from traffic. In contrast, the contribution of indoor sources to personal exposure to PM 2.5 and UFP seems to be greater than from outdoor traffic sources. This is probably related to a combination of the type of building construction and a varying range of activities conducted indoors. It is recommended to ensure a good ventilation during cooking to minimize exposure to cooking aerosols.
Given that many people typically spend the majority of their time at home, accurate measurement and modelling of the home environment is critical in estimating their exposure to air pollution. This study investigates the fate and impact on human exposure of outdoor and indoor pollutants in London homes, using a combination of sensor measurements, outdoor air pollution estimated from the CMAQ-urban model and indoor mass balance models. Averaged indoor concentrations of PM2.5, PM10 and NO2 were 14.6, 24.7 and 14.2 μg m⁻³ while the outdoor concentrations were 14.4, 22.6 and 21.4 μg m⁻³, respectively. Mean infiltration factors of particles (0.6–0.7) were higher than those of NO2 (0.4). In contrast, higher loss rates were found for NO2 (0.5–0.8 h⁻¹) compared to those for particles (0.1–0.3 h⁻¹). The average concentrations of PM2.5, PM10 and NO2 in kitchen environments were 22.0, 33.7 and 20.8 μg m⁻³, with highest hourly concentrations (437, 644 and 136 μg m⁻³, respectively) during cooking times (6–7 pm). Indoor sources increased the indoor concentrations of particles and NO2 by an average of 26–37% in comparison to the indoor background level without indoor sources. Outdoor and indoor air exchange plays an important role in reducing air pollution indoors by 65–86% for particles and 42–65% for NO2.
Traffic is the key source of ultrafine particles (UFPs, particulate matter with a diameter less than 0.1 μm or 100 nm) in most urban areas. The traffic-generated UFPs vented out from an urban street mix with overlying ‘urban background air’ and are diluted whilst also undergoing change due to condensation/evaporation and other aerosol microphysics. Traffic-generated UFPs are comprised of a complex mixture of semi-volatile compounds (SVOCs) with volatility varying over many orders of magnitude, resulting in size-dependent particle composition. This study coupled the multicomponent microphysics (involving condensation/evaporation) of UFPs with the WRF v3.6.1 (Weather Research and Forecasting) large eddy simulation model (i.e. WRF-LES-UFP), and used this modelling system to investigate the general behaviour of UFPs on the neighbourhood scale (10-1000 m; transport times of few minutes) for idealised scenarios. The model captures the horizontal dispersion of UFPs downwind into the neighbourhood scale and vertical mixing with urban background air. Evaporation decreases the mode size of UFPs venting into the urban boundary layer from street-level. The neighbourhood-scale evolution of UFPs is, therefore, a combination of the effects of emissions, mixing with background, and condensation/evaporation. Total UFP number concentration and total mass concentrations scale linearly with the emission rate or the background concentration, demonstrating numerical conservation of the scheme. The linearity is less pronounced for the number concentration of smaller particles (UFP diameter less than 100 nm) with respect to UFP size and concentrations of those organic compounds with a time scale comparable to the dilution time scale (in the order of minutes), reflecting the effects (altering the particle sizes) due to condensation/evaporation.
Time–activity diaries kept by members of the general public indicate that on average people spend around 90% of their time indoors, this is associated with considerable exposure to air pollutants as not only is there infiltration of pollutants from outdoors, there are also emissions indoors that can lead to elevated pollutant concentrations. Despite this, and the fact that the WHO produces air quality guidelines for indoor air, the only statutory requirements for monitoring of airborne pollutant concentrations relate to the outdoor environment. Given its importance as a source of air pollution exposure, increasing attention is being given to pollution of the indoor environment.
This volume considers both chemical and biological pollutants in the indoor atmosphere from their sources to chemical and physical transformations, human exposure and potential effects on human health. It is a valuable reference for those working in in environmental policy, civil and environmental engineering as well as for atmospheric chemists.
Nanoparticles emitted from road traffic are the largest source of respiratory exposure for the general public living in urban areas. It has been suggested that adverse health effects of airborne particles may scale with airborne particle number, which if correct, focuses attention on the nanoparticle (less than 100 nm) size range which dominates the number count in urban areas. Urban measurements of particle size distributions have tended to show a broadly similar pattern dominated by a mode centred on 20–30 nm diameter emitted by diesel engine exhaust. In this paper we report the results of measurements of particle number concentration and size distribution made in a major London park as well as on the BT Tower, 160 m aloft. These measurements taken during the REPARTEE project (Regents Park and BT Tower experiment) show a remarkable shift in particle size distributions with major losses of the smallest particle class as particles are advected away from the traffic source. In the Park, the traffic related mode at 20–30 nm diameter is much reduced with a new mode at <10 nm. Size distribution measurements also revealed higher number concentrations of sub-50 nm particles at the BT Tower during days affected by higher turbulence as determined by Doppler Lidar measurements and are indicative of loss of nanoparticles from air aged during less turbulent conditions. These results are suggestive of nanoparticle loss by evaporation, rather than coagulation processes. The results have major implications for understanding the impacts of traffic-generated particulate matter on human health.
Urban ambient aerosols have been of much concern in recent decades due to their effects upon both atmospheric processes and human health. This study aimed to apportion the sources of submicron particles measured at an urban background area in London and to identify which sources are most responsible for particles deposited in the human lung. Particle number size distributions (PNSD) measured by a Scanning Mobility Particle Sizer (TSI, USA), covering the size range of 16.5–604 nm at the London North Kensington background sampling site during 2012 were used in a Positive Matrix Factorization (PMF) model to apportion to six dominant sources of particles. These included local traffic emissions (26.6% by number), aged traffic emissions (29.9%), urban accumulation mode (28.3%), nucleation (6.5%), inorganic secondary aerosol (1.7%) and mixed secondary aerosol (6.9%). Based on the ICRP model, the total deposition efficiencies of submicron particles for the aforementioned sources in the human respiratory tract were 0.57, 0.41, 0.24, 0.62, 0.24 and 0.24, respectively. In terms of source apportionment of particles deposited in the lung, traffic emissions represent the main source of particles deposited by number in both the regional and total lung, accounting for 59 to 71% of total deposited particles, followed by regional accumulation mode (17%) and nucleation (10%) particles. Secondary aerosols only account for 5.1% of total deposited particles by number, but they represent the main source of particles deposited in the lung expressed as surface area (44.6%) and volume (72.3%) of total deposition. The urban accumulation mode contributes 27.3% and 17.3% of total deposited particles by surface area and volume, while traffic emissions contribute 26.6% and 9.7%, respectively. Nucleation contributes only 1.6% and 0.7% of total deposited particles by surface area and volume.
Earlier work has demonstrated the potential for volatilisation of nanoparticles emitted by road traffic as these are advected downwind from the source of emissions, but there have been few studies and the processes have yet to be elucidated in detail. Using a dataset collected at paired sampling sites located respectively in a street canyon and in a nearby park, an in depth analysis of particle number size distributions has been conducted in order to better understand the size reduction of the semi-volatile nanoparticles. By sorting the size distributions according to wind direction and fitting log normal modes, it can be seen that the mode peaking at around 22 nm at the street canyon site is on average shrinking to 6.2 nm diameter at the park site which indicates a mean shrinkage rate for these particles of 0.13 nm s-1 with temperatures within the range 12-18ºC. The diurnal variation of the shrunken mode in the park reflects the diurnal pattern of particle concentrations at the street canyon site taken as the main source area. An analysis of peak diameter for the smallest mode at the downwind park site shows an inverse relationship to wind speed suggesting that dilution rather than travel time is the main determinant of the particle shrinkage rate. An evaluation of previously collected C10 to C35 n-alkane data from a different urban location shows a good fit to Pankow partitioning theory reflecting the semi-volatility of compounds believed to be representative of the composition of diesel exhaust nanoparticles, hence confirming the feasibility of an evaporative mechanism for particle shrinkage.
The particle number size distribution (PNSD) of airborne particles not only provides us with information about sources and atmospheric processing of particles, but also plays an important role in determining regional lung dose. As a result, urban particles and their size distributions have received much attention with a rapid increase of publications in recent years. The object of this review is to synthesise and analyse existing knowledge on particles in urban environments with a focus on their number concentration and size distribution. This study briefly reviews the characterization of PNSD from seven major sources of urban particles including traffic emissions, industrial emissions, biomass burning, cooking, transported aerosol, marine aerosol and nucleation. It then discusses atmospheric physical processes such as coagulation or condensation which have a strong influence on PNSD. Finally, the implications of PNSD datasets for source modelling are briefly discussed. Based on this review, it is concluded that the concentrations, modal structures and temporal patterns of urban particles are strongly influenced by traffic emissions, which are identified as the main source of particle number in urban environments. Information derived from particle number size distributions is beginning to play an important role in source apportionment studies.
Rationale:
Few studies have been performed on air pollution effects on lung function in the elderly, a vulnerable population with low reserve capacity, and even fewer have looked at changes in the rate of lung function decline.
Objectives:
We evaluated the effect of long-term exposure to black carbon on levels and rates of decline in lung function in the elderly.
Methods:
FVC and FEV1 were measured one to six times during the period 1995-2011 in 858 men participating in the Normative Aging Study. Exposure to black carbon, a tracer of traffic emissions, was estimated by a spatiotemporal land use regression model. We investigated the effects of moving averages of black carbon of 1-5 years before the lung function measurement using linear mixed models.
Measurements and main results:
A 0.5 μg/m(3) increase in long-term exposure to black carbon was associated with an additional rate of decline in FVC and FEV1 of between 0.5% and 0.9% per year, respectively, depending on the averaging time. In addition, black carbon exposure before the baseline visit was associated with lower levels of both FVC and FEV1, with effect estimates increasing up to 6-7% with a 5-year average exposure.
Conclusions:
Our results support adverse effects of long-term exposure to traffic particles on lung function level and rate of decline in the elderly and suggest that functionally significant differences in health and risk of disability occur below the annual Environmental Protection Agency National Air Quality Standards.
Indoor ultrafine particles (UFP, < 100 nm)undergo aerosol processes such as coagulation and deposition, which alter UFP size distribution and accordingly the level of exposure to UFP of different sizes. This study investigates the decay of indoor UFP originated from five different sources: a gas stove and an electric stove, a candle, a hair dryer, and power tools in a residential test building. An indoor aerosol model was developed to investigate differential effects of coagulation,deposition and ventilation.The coagulation model includes Brownian, van der Waals and viscosity forces, and also fractal geometry for particles > 24 nm. The model was parameterized using different values of the Hamaker constant for predicting the coagulation rate. Deposition was determined for two different conditions: central fan on vs. central fan off. For the case of a central fan running, deposition rates were measured by using a nonlinear solution to the mass balance equation for the whole building. For the central fan off case, an empirical model was used to estimate deposition rates. Ventilation was measured continuously using an automated tracer gas injection and sampling system.The study results show that coagulation isa significantaerosol process forUFP dynamics and the primary cause for the shift of particle size distribution following an episodic high-concentration UFP release with no fans on‥ However, with the central mechanical fan on, UFP deposition loss is substantial and comparable to the coagulation loss. These results suggest that coagulation should be considered during high concentration periods (> 20, 000 cm), while particle deposition should be treated as a major loss mechanism when air recirculates through ductwork or mechanical systems.
openair is an R package primarily developed for the analysis of air pollution measurement data but which is also of more general use in the atmospheric sciences. The package consists of many tools for importing and manipulating data, and undertaking a wide range of analyses to enhance understanding of air pollution data. In this paper we consider the development of the package with the purpose of showing how air pollution data can be analysed in more insightful ways. Examples are provided of importing data from UK air pollution networks, source identification and characterisation using bivariate polar plots, quantitative trend estimates and the use of functions for model evaluation purposes. We demonstrate how air pollution data can be analysed quickly and efficiently and in an interactive way, freeing time to consider the problem at hand. One of the central themes of openair is the use of conditioning plots and analyses, which greatly enhance inference possibilities. Finally, some consideration is given to future developments.
This thesis discusses the development of a gas, aerosol, transport, and
radiation air quality model (GATOR), the coupling of GATOR to a
mesoscale meteorological and tracer dispersion model (MMTD), and the
application of the resulting GATOR/MMTD air pollution modeling system
(APMS) to studies of gas and aerosol pollution buildup in the Los
Angeles Basin. GATOR consists of computer algorithms that simulate four
groups of atmospheric processes: gas, aerosol, transport, and radiation
processes. Gas processes include chemistry, emissions, gas-to-particle
conversion, optical depth attenuation, and deposition. Aerosol processes
include size-resolved emissions, nucleation, coagulation, condensational
growth, dissolutional growth, evaporation, chemical equilibrium, aqueous
chemistry, optical depth attenuation, deposition, and sedimentation.
Transport processes include horizontal advection and diffusion and
vertical diffusion of all gases and particles, and they require
meteorological data as inputs. To drive the transport processes, the
MMTD, developed by R. Lu and R. P. Turco, was coupled to GATOR. The MMTD
predicts wind speed, wind direction, temperature, humidity, and
pressure, among other variables. Finally, radiation processes in GATOR
include spectrally-resolved scattering and absorption by gases,
aerosols, fogs, and clouds, and calculation of mean intensities and
heating rates. I used the GATOR/MMTD modeling system to predict
pollution buildup in Los Angeles during the Southern California Air
Quality Study (SCAQS) period of August 26-28, 1987. Among the model
inputs were emissions, soil moisture, albedo, topographical, landuse,
and chemical rate data. To validate the model, surface observations were
compared to model predictions of gas-phase ozone, nitric oxide, nitrogen
dioxide, carbon monoxide, sulfur dioxide, methane, total non-methane
hydrocarbons, formaldehyde, peroxyacetylnitrate, hydrogen peroxide,
nitric acid, nitrous acid, and ammonia concentrations. Observations were
also compared to predictions of aerosol-phase ammonium, nitrate, sodium,
chloride, sulfate, and total particulate concentrations. Finally,
observations were compared to predictions of solar radiation and
scattering coefficients. In sum, the GATOR/MMTD system predicted ozone
to within a normalized gross error of 20 -35% during the study period.
Additional statistics and time-series plots are shown.
An advanced receptor model was used to elicit source information based on ambient submicron (0.01-0.47 mu m) particle number concentrations, gaseous species, and meteorological variables measured at the New York State Department of Environmental Conservation central monitoring site in Rochester, NY. Four seasonal data sets (winter, spring, summer, and fall) were independently investigated. A total of ten different sources were identified, including two traffic factors, two nucleation factors, industrial emissions, residential/commercial heating, secondary nitrate, secondary sulfate, ozone-rich secondary aerosol, and regionally transported aerosol. The resolved sources were generally characterized by similar number modes for either winter, spring, summer or fall. The size distributions for nucleation were dominated by the smallest particles (<10-30 nm) that gradually grew to larger sizes as could be seen by observing the volume profiles. In addition, the nucleation factors were closely linked to traffic rush hours suggesting that cooling of tail-pipe emissions may have induced nucleation activity in the vicinity of the highways. Although the diurnal pattern of each of the two traffic factors closely followed traffic rush hour for Rochester, their size modes were different suggesting that these factors might represent local and remote emissions. Industrial emissions were dominated by emissions from coal-fired power plants that were located to the northwest of the sampling site. These facilities represent the largest point emission sources Of SO(2), and probably ultrafine (<0.1 mu m) or submicron particles, in Rochester. Regionally transported material was characterized by accumulation mode particles. Air parcel back-trajectories showed transport of air masses from the industrial midwest.
An Ultrafine Water-based Condensation Particle Counter (UWCPC), a Scanning Mobility Particle Sizer (SMPS) incorporating an UWCPC, and a Fast Mobility Particle Sizer (FMPS) were deployed to determine the number and size distribution of ultrafine particles. Comparisons of particle number concentrations measured by the UWCPC, SMPS, and FMPS were conducted to evaluate the performance of the two particle sizers using ambient particles as well as lab generated artificial particles. The SMPS number concentration was substantially lower than the FMPS (FMPS/SMPS = 1.56) measurements mainly due to the diffusion losses of particles in the SMPS. The diffusion loss corrected SMPS (C-SMPS) number concentration was on average 15% higher than the FMPS data (FMPS/C-SMPS = 0.87). Good correlation between the C-SMPS and FMPS was also observed for the total particle number concentrations in the size range 6 nm to 100 nm measured at a road-side urban site (r2 = 0.91). However, the particle size distribution measured by the C-SMPS was quite different from the size distribution measured by the FMPS. An empirical correction factor for each size bin was obtained by comparing the FMPS data to size-segregated UWCPC number concentrations for atmospheric particles. The application of the correction factor to the FMPS data (C-FMPS) greatly improved the agreement of the C-SMPS and C-FMPS size distributions. The agreement of the total particle concentrations also improved to well within 10% (C-FMPS/C-SMPS = 0.95).
Aerosol emissions from vegetation fires have a large impact on air quality and climate. In this study, we use published experimental data and different fitting procedures to derive dynamic particle number and mass emission factors (EFPN, EFPM) related to the fuel type, burning conditions and the mass of dry fuel burned, as well as characteristic CO-referenced emission ratios (PN/CO, PM/CO). Moreover, we explore and characterize the variability of the particle size distribution of fresh smoke, which is typically dominated by a lognormal accumulation mode with count median diameter around 120 nm (depending on age, fuel and combustion efficiency), and its effect on the relationship between particle number and mass emission factors. For the particle number emission factor of vegetation fires, we found no dependence on fuel type and obtained the following parameterization as a function of modified combustion efficiency (MCE): EFPN=34·1015×(1-MCE) kg−1±1015 kg−1 with regard to dry fuel mass (d.m.). For the fine particle mass emission factors (EFPM) we obtained (86–85×MCE) g kg−1±3 g kg−1 as an average for all investigated fires; (93–90×MCE) g kg
The overall aim of our investigation was to quantify the magnitude and range of individual personal exposures to a variety of air toxics and to develop models for exposure prediction on the basis of time-activity diaries. The specific research goals were (1) to use personal monitoring of non-smokers at a range of residential locations and exposures to non-traffic sources to assess daily exposures to a range of air toxics, especially volatile organic compounds (VOCs) including 1,3-butadiene and particulate polycyclic aromatic hydrocarbons (PAHs); (2) to determine microenvironmental concentrations of the same air toxics, taking account of spatial and temporal variations and hot spots; (3) to optimize a model of personal exposure using microenvironmental concentration data and time-activity diaries and to compare modeled exposures with exposures independently estimated from personal monitoring data; (4) to determine the relationships of urinary biomarkers with the environmental exposures to the corresponding air toxic. Personal exposure measurements were made using an actively pumped personal sampler enclosed in a briefcase. Five 24-hour integrated personal samples were collected from 100 volunteers with a range of exposure patterns for analysis of VOCs and 1,3-butadiene concentrations of ambient air. One 24-hour integrated PAH personal exposure sample was collected by each subject concurrently with 24 hours of the personal sampling for VOCs. During the period when personal exposures were being measured, workplace and home concentrations of the same air toxics were being measured simultaneously, as were seasonal levels in other microenvironments that the subjects visit during their daily activities, including street microenvironments, transport microenvironments, indoor environments, and other home environments. Information about subjects' lifestyles and daily activities were recorded by means of questionnaires and activity diaries. VOCs were collected in tubes packed with the adsorbent resins Tenax GR and Carbotrap, and separate tubes for the collection of 1,3-butadiene were packed with Carbopack B and Carbosieve S-III. After sampling, the tubes were analyzed by means of a thermal desorber interfaced with a gas chromatograph-mass spectrometer (GC-MS). Particle-phase PAHs collected onto a quartz-fiber filter were extracted with solvent, purified, and concentrated before being analyzed with a GC-MS. Urinary biomarkers were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS-MS). Both the environmental concentrations and personal exposure concentrations measured in this study are lower than those in the majority of earlier published work, which is consistent with the reported application of abatement measures to the control of air toxics emissions. The environmental concentration data clearly demonstrate the influence of traffic sources and meteorologic conditions leading to higher air toxics concentrations in the winter and during peak-traffic hours. The seasonal effect was also observed in indoor environments, where indoor sources add to the effects of the previously identified outdoor sources. The variability of personal exposure concentrations of VOCs and PAHs mainly reflects the range of activities the subjects engaged in during the five-day period of sampling. A number of generic factors have been identified to influence personal exposure concentrations to VOCs, such as the presence of an integral garage (attached to the home), exposure to environmental tobacco smoke (ETS), use of solvents, and commuting. In the case of the medium- and high-molecular-weight PAHs, traffic and ETS are important contributions to personal exposure. Personal exposure concentrations generally exceed home indoor concentrations, which in turn exceed outdoor concentrations. The home microenvironment is the dominant individual contributor to personal exposure. However, for those subjects with particularly high personal exposures, activities within the home and exposure to ETS play a major role in determining exposure. Correlation analysis and principal components analysis (PCA) have been performed to identify groups of compounds that share common sources, common chemistry, or common transport or meteorologic patterns. We used these methods to identify four main factors determining the makeup of personal exposures: fossil fuel combustion, use of solvents, ETS exposure, and use of consumer products. Concurrent with sampling of the selected air toxics, a total of 500 urine samples were collected, one for each of the 100 subjects on the day after each of the five days on which the briefcases were carried for personal exposure data collection. From the 500 samples, 100 were selected to be analyzed for PAHs and ETS-related urinary biomarkers. Results showed that urinary biomarkers of ETS exposure correlated strongly with the gas-phase markers of ETS and 1,3-butadiene. The urinary ETS biomarkers also correlated strongly with high-molecular-weight PAHs in the personal exposure samples. Five different approaches have been taken to model personal exposure to VOCs and PAHs, using 75% of the measured personal exposure data set to develop the models and 25% as an independent check on the model performance. The best personal exposure model, based on measured microenvironmental concentrations and lifestyle factors, is able to account for about 50% of the variance in measured personal exposure to benzene and a higher proportion of the variance for some other compounds (e.g., 75% of the variance in 3-ethenylpyridine exposure). In the case of the PAHs, the best model for benzo[a]pyrene is able to account for about 35% of the variance among exposures, with a similar result for the rest of the PAH compounds. The models developed were validated by the independent data set for almost all the VOC compounds. The models developed for PAHs explain some of the variance in the independent data set and are good indicators of the sources affecting PAH concentrations but could not be validated statistically, with the exception of the model for pyrene. A proposal for categorizing personal exposures as low or high is also presented, according to exposure thresholds. For both VOCs and PAHs, low exposures are correctly classified for the concentrations predicted by the proposed models, but higher exposures were less successfully classified.
Aerosol emissions from vegetation fires have a large impact on air quality and climate. In this study, we use published experimental data and different fitting procedures to derive dynamic particle number and mass emission factors (EFPN, EFPM) related to the fuel type, burning conditions and the mass of dry fuel burned, as well as characteristic CO-referenced emission ratios (PN/CO, PM/CO). Moreover, we explore and characterize the variability of the particle size distribution of fresh smoke, which is typically dominated by a lognormal accumulation mode with count median diameter around 120 nm (depending on age, fuel and combustion efficiency), and its effect on the relationship between particle number and mass emission factors. For the particle number emission factor of vegetation fires, we found no dependence on fuel type and obtained the following parameterization as a function of modified combustion efficiency (MCE): EFPN=34·1015×(1-MCE) kg−1±1015 kg−1 with regard to dry fuel mass (d.m.). For the fine particle mass emission factors (EFPM) we obtained (86–85×MCE) g kg−1±3 g kg−1 as an average for all investigated fires; (93–90×MCE) g kg±4 g kg−1 for forest; (67–65×MCE) g kg±2 g kg−1 for savanna; (63–62×MCE) g kg±1 g kg−1 for grass. For the PN/CO emission ratio we obtained an average of (34±16) cm−3 ppb−1 exhibiting no systematic dependence on fuel type or combustion efficiency. The average PM/CO emission ratios were (0.09±0.04) g g−1 for all investigated fires, (0.13±0.05) g g−1 for forest; (0.08±0.03) g g−1 for savanna; and (0.07±0.03) g g−1 for grass. The results are consistent with each other, given that particles from forest fires are on average larger than those from savanna and grass fires. This assumption and the above parameterizations represent the current state of knowledge, but they are based on a rather limited amount of experimental data which should be complemented by further measurements. Nevertheless, the presented parameterizations appear sufficiently robust for exploring the influence of vegetation fires on aerosol particle number and mass concentrations in regional and global model studies.
Exposure to ambient fine particles [particulate matter < or = 2.5 microm diameter (PM(2.5))] is a potential factor in the exacerbation of asthma. National air quality particle standards consider total mass, not composition or sources, and may not protect against health impacts related to specific components.
We examined associations between daily exposure to fine particle components and sources, and symptoms and medication use in children with asthma.
Children with asthma (n = 149) 4-12 years of age were enrolled in a year-long study. We analyzed particle samples for trace elements (X-ray fluorescence) and elemental carbon (light reflectance). Using factor analysis/source apportionment, we identified particle sources (e.g., motor vehicle emissions) and quantified daily contributions. Symptoms and medication use were recorded on study diaries. Repeated measures logistic regression models examined associations between health outcomes and particle exposures as elemental concentrations and source contributions.
More than half of mean PM(2.5) was attributed to traffic-related sources motor vehicles (42%) and road dust (12%). Increased likelihood of symptoms and inhaler use was largest for 3-day averaged exposures to traffic-related sources or their elemental constituents and ranged from a 10% increased likelihood of wheeze for each 5-microg/m(3) increase in particles from motor vehicles to a 28% increased likelihood of shortness of breath for increases in road dust. Neither the other sources identified nor PM(2.5) alone was associated with increased health outcome risks.
Linking respiratory health effects to specific particle pollution composition or sources is critical to efforts to protect public health. We associated increased risk of symptoms and inhaler use in children with asthma with exposure to traffic-related fine particles.
The surface interactions of nicotine and phenanthrene with carpet, painted wallboard, and stainless steel were investigated in a room-sized environmental test chamber. Adsorption kinetics were tested by flash evaporating a known mass of each compound into a sealed 20 m3 chamber containing one or more of the tested sorbents. In each experiment, one or more emissions were performed after the gas-phase concentration had reached an apparent plateau. At the end of each experiment, the chamber was ventilated and resealed to monitor reemission of the compound from the sorbents. Kinetic sorption parameters were determined by fitting a mass-balance model to the experimental results. The sorption capacity of stainless steel was of similar magnitude for nicotine and phenanthrene. Sorption of nicotine on carpet and wallboard was much stronger, with equilibrium partitioning values 2-3 orders of magnitude higher. The sorption capacities of phenanthrene on carpet and wallboard were smaller, approximately 10-20% of the stainless steel values. The rates of uptake are of similar magnitude for all sorbate--sorbent pairs and are consistent with the limit imposed by gas-phase boundary-layer mass transport. The rates of desorption are much faster for phenanthrene than for nicotine. Model simulations predict average nicotine levels in a typical smoking residence that are consistent with published data.
In this paper, several factors influencing particle deposition in indoor environments are analyzed with an analytical model and a three-dimensional drift flux model combined with the particle deposition boundary conditions for wall surfaces. The influences of flow conditions near the wall surfaces, surface roughness and particle concentration distribution on particle deposition indoors are studied. By modeling particle deposition onto surfaces with the analytical model, it is found that larger friction velocity near the wall surfaces and rougher surface may lead to larger particle deposition velocity when the particle size is small, but when particle size is large enough (the range is up to the actual friction velocity and in this study it is about 1-5 microm), the influence of the friction velocity and roughness could be neglected. Furthermore, the three-dimensional numerical simulations indicate that particle concentration distribution may be very different even for the same particle source and air change rate, which cause a different deposited particle flux. As the particle concentration distribution may not be uniform in most cases, especially for the ventilated rooms, it is important to incorporate particle concentration distribution when analyzing particle deposition in indoor environments. Some suggestions or rules for particle deposition controlling are also presented based on the analysis.
This paper describes the use of a unique valve switching system that allowed for high temporal resolution indoor and outdoor data to be collected concurrently from online C-ToF-AMS, SMPS and OC/EC, and offline BLPI measurements. The results reveal near real-time dynamic aerosol behaviour along a migration path from an outdoor to indoor environment.
A number of major research questions remain concerning the sources and properties of road traffic generated particulate matter. A full understanding of the composition of primary vehicle exhaust aerosol and its contribution to secondary organic aerosol (SOA) formation still remains elusive, and many uncertainties exist relating to the semi-volatile component of the particles. Semi-Volatile Organic Compounds (SVOCs) are compounds which partition directly between the gas and aerosol phases under ambient conditions. The SVOCs in engine exhaust are typically hydrocarbons in the C15-C35 range, and are largely uncharacterised because they are unresolved by traditional gas chromatography, forming a large hump in the chromatogram referred to as Unresolved Complex Mixture (UCM). In this study, thermal desorption coupled to comprehensive Two Dimensional Gas-Chromatography Time-of-Flight Mass-Spectrometry (TD-GC × GC-ToF-MS) was exploited to characterise and quantify the composition of SVOCs from the exhaust emission. Samples were collected from the exhaust of a diesel engine, sampling before and after a diesel oxidation catalyst (DOC), while testing at steady state conditions. Engine exhaust was diluted with air and collected using both filter and impaction (nano-MOUDI), to resolve total mass and size resolved mass respectively. Adsorption tubes were utilised to collect SVOCs in the gas phase and they were then analysed using thermal desorption, while particle size distribution was evaluated by sampling with a DMS500. The SVOCs were observed to contain predominantly n-alkanes, branched alkanes, alkyl-cycloalkanes, alkyl-benzenes, PAHs and various cyclic aromatics. Particle phase compounds identified were similar to those observed in engine lubricants, while vapour phase constituents were similar to those measured in fuels. Preliminary results are presented illustrating differences in the particle size distribution and SVOCs composition when collecting samples with and without a DOC. The results indicate that the DOC tested is of very limited efficiency, under the studied engine operating conditions, for removal of SVOCs, especially at the upper end of the molecular weight range.
Cited By (since 1996): 81
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Export Date: 4 February 2013
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Author Address: Environmental and Occupational Health Sciences Institute, University of Medicine and Dentistry of New Jersey, Rutgers University, Piscataway, NJ 08854, United States
Author Address: International Centre for Indoor Environment and Energy, Technical University of Denmark, DK-2800 Lyngby, Denmark
Author Address: Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710, United States
An analysis is carried out to determine the combined effect of van der Waals and viscous fluid forces on coagulation of spherical aerosol particles in the free molecular, transition, and continuum regimes. The effect of viscous forces is taken into account by modifying the particle diffusion coefficient. An asymptotic solution is substituted for the classical formulation of viscous forces. The results of free molecular and continuum regimes are then extended to the transition size range by an interpolation formula.
In residential environments without the operation of mechanical ventilation, infiltration becomes the dominant ventilation mode and deposition on material surface is one of the major particle losses, while penetration determines how much ambient particle can be brought from outside into the indoor environment. This study presents results based on measurements conducted in six non-smoking residences in high-rise apartment buildings. The effect of particle size from 0.02 to 10μm was evaluated. A simplified indoor particle model was constructed to facilitate the calculation. The deposition rate and the penetration coefficient were determined according to a decay rate constant and the steady-state particle concentration in the transient form of the indoor particle concentration decay profile. Both of them were particle-size dependent but showed a different up-and-down inversion profile against the particle size. The major causes of the depositional losses and the penetration effects are diffusion, inertial impaction/interception and settling. They reduce the penetration and enhance the deposition in the size ranges of ultra-fine and coarse mode particles. The penetration coefficient showed a hill-shape with respect to particle sizes and there was a peak (0.79) at the size range of 0.853–1.382μm. It decreased on both smaller and larger particle size ranges and the minimum particle penetration coefficient was 0.48 at the particle size range 4.698–9.647μm. Deposition rate showed a converse shape with maximum values at both the smallest and the largest particle size ranges: 1.16×10−4ms−1 for 4.698–9.647μm and 0.6×10−4ms−1 for 0.02–1.00μm. The lowest deposition velocity was 0.31×10−4ms−1 (0.542–0.777μm) that was about four times less than the maximum deposition velocity.
Particle deposition to indoor surfaces is frequently modeled by assuming that indoor air flow is homogeneously and isotropically turbulent. Existing formulations of such models, based on the seminal work of Corner and Pendlebury (1951, Proc. Phys. Soc. Lond.B 64, 645), lack a thorough physical foundation. We apply the results of recent studies of near-surface turbulence to produce an analogous model for particle deposition onto indoor surfaces that remains practical to use yet has a stronger physical basis. The model accounts for the effects of Brownian and turbulent diffusion and gravitational settling. It predicts deposition to smooth surfaces as a function of particle size and density. The only required input parameters are enclosure geometry and friction velocity. Model equations are presented for enclosures with vertical and horizontal surfaces, and for spherical cavities. The model helps account for a previously unexplained experimental observation regarding the functional dependence of deposition velocity on particle size. Model predictions agree well with recently published experimental data for a spherical cavity (Cheng, Y. S., Aerosol Sci. Technol. 27, 131–146, (1997)).
A large study on the comparability of various aerosol instruments was conducted. The study involved altogether 24 instruments, including eleven scanning, sequential and fast mobility particle sizers (five Grimm SMPS+C, three TSI SMPS and three FMPS) with different settings and differential mobility analyzers (DMAs), twelve instruments based on unipolar diffusion charging to determine size integrated concentrations and in some cases mean particle size (five miniDiSCs of the University of Applied Sciences and Arts Northwestern Switzerland, four Philips Aerasense nanoTracers, two TSI Nanoparticle Surface Area Monitors and one Grimm nanoCheck) and one TSI ultrafine condensation particle counter (UCPC). All instruments were simultaneously challenged with particles of various sizes, concentrations and morphologies. All measurement results were compared with those from a freshly calibrated SMPS for size distributions and the UCPC for number concentration. In general, all SMPSs showed good comparability with particularly the sizing agreeing to within a few percent. Differences in the determined number concentration were somewhat more pronounced, but the largest deviations could be tracked back to the use of an older software version. The comparability of the FMPSs was shown to be lower, with discrepancies on the order of ±25% for sizing and ±30% for total concentrations. The discrepancies between FMPSs and the internal reference SMPS seemed to be influenced by particle size and morphology. Total number and/or lung deposited surface area concentrations measured with unipolar diffusion charger based instruments generally agreed to within ±30% with the internal references (CPC for number concentrations; lung deposited surface area derived from SMPS measurements), as long as the particle size distributions of the test aerosols were within the specified limits for the instruments. When the upper size limit was exceeded, deviations of up to several hundred percent were detected.
: Seasonal and regional differences have been reported for the increase in short-term mortality associated with a given increase in the concentration of outdoor particulate matter with an aerodynamic diameter smaller than 10 μm (PM10 mortality coefficient). Some of this difference may be because of seasonal and regional differences in indoor exposure to PM10 of outdoor origin.
: From a previous study, we obtained PM10 mortality coefficients for each season in seven U.S. regions. We then estimated the change in the sum of indoor and outdoor PM10 exposure per unit change in outdoor PM10 exposure (PM10 exposure coefficient) for each season in each region. This was originally accomplished by estimating PM10 exposure coefficients for 19 cities within the regions for which we had modeled building infiltration rates. We subsequently expanded the analysis to include 64 additional cities with less well-characterized building infiltration rates.
: The correlation (r = 0.71 [95% confidence interval = 0.46 to 0.86]) between PM10 mortality coefficients and PM10 exposure coefficients (28 data pairs; four seasons in each of seven regions) was strong using exposure coefficients derived from the originally targeted 19 National Morbidity, Mortality, and Air Pollutions Study cities within the regions. The correlation remained strong (r = 0.67 [0.40 to 0.84]) when PM10 exposure coefficients were derived using 83 cities within the regions (the original 19 plus the additional 64).
: Seasonal and regional differences in PM10 mortality coefficients appear to partially reflect seasonal and regional differences in total PM10 exposure per unit change in outdoor exposure.
Measurements of the size distribution of particles emitted from a modern heavy duty diesel engine using fuel with a sulfur content of between 0.03 and 0.05% by mass have been made under constant engine operating conditions, but with variations in the humidity of dilution air and dilution ratio prior to particle size measurement. The results show clearly that the measured size distribution is crucially dependent upon the conditions of dilution, hence creating real difficulties for comparison of data between different investigators. Conditions of high dilution ratio and high relative humidity both tend to favor the production of nanoparticles, especially within the range below 50 nm diameter. Application of homogeneous nucleation theory shows that nanoparticle production during dilution is qualitatively consistent with the production of sulfuric acid, hut the predicted nucleation rates are lower than those measured, in common with studies of nucleation in the atmosphere. Chemical analysis of size-fractionated particles shows enhancement of sulfate concentrations in humid dilution conditions and at high dilution ratios consistent with the above mechanism. The possible role of semivolatile organic compounds in these processes has not been investigated.
Epidemiologic evidence indicates a relationship between outdoor particle exposure and adverse health effects, while most people spend 85–90% of their time indoors, thus understanding the relationship between indoor and outdoor particles is quite important. This paper aims to provide an up-to-date revision for both experiment and modeling on relationship between indoor and outdoor particles. The use of three different parameters: indoor/outdoor (I/O) ratio, infiltration factor and penetration factor, to assess the relationship between indoor and outdoor particles were reviewed. The experimental data of the three parameters measured both in real houses and laboratories were summarized and analyzed. The I/O ratios vary considerably due to the difference in size-dependent indoor particle emission rates, the geometry of the cracks in building envelopes, and the air exchange rates. Thus, it is difficult to draw uniform conclusions as detailed information, which make I/O ratio hardly helpful for understanding the indoor/outdoor relationship. Infiltration factor represents the equilibrium fraction of ambient particles that penetrates indoors and remains suspended, which avoids the mixture with indoor particle sources. Penetration factor is the most relevant parameter for the particle penetration mechanism through cracks and leaks in the building envelope. We investigate the methods used in previously published studies to both measure and model the infiltration and penetration factors. We also discuss the application of the penetration factor models and provide recommendations for improvement.
Es werden die Grundlagen zu einer allgemeinen Theorie der raschen Koagulation entwickelt unter Benützung der folgenden Postulate:
1.
Für das Zusammenhaften zweier Micellen ist Berührung derer Oberflächen notwendig.
2.
Die Häufigkeit der Zusammenstöße von Teilchen ist durch die Temperaturbewegung und die Strömung der Teilchen bestimmt.
3.
Für die Koagulation an ein Einzelteilchen ist nur die stationäre Teilchenverteilung um dasselbe maßgebend.
Die Anwendung dieser Theorie auf strömungslose monodisperse Systeme führt zu einer Theorie der Koagulation von Blättchen-
und Stäbchenkolloiden. Es zeigt sich, daß Blättchenkolloide angenähert gleich koagulieren wie Sole mit Kugelteilchen, daß
dagegen stäbchenförmige Teilchen eine viel größere Koagulationsgeschwindigkeit haben können.
Es wird der Einfluß der Polydispersität der Sole untersucht und ein Zusammenhang zwischen der Verteilungskurve der Radien
in einem Ausgangskolloid mit kugelförmigen Teilchen und der Anfangstangente der Koagulationskurve abgeleitet. Angenähert monodisperse
Systeme müssen innerhalb der Fehlergrenze der Messungen nach v. Smoluchowski koagulieren, stark polydisperse Systeme dagegen
koagulieren rascher.
Es wird der Einfluß der Sedimentation und des Rührens diskutiert unter Berücksichtigung der Stokesschen Strömung um die bewegten
Teilchen. Es ergibt sich, daß diese Effekte nur die Koagulation größerer Teilchen beeinflussen, und es werden Formeln für
die minimalen Teilchenradien gegeben, für die die Effekte beobachtet werden können.
Aerosol particle number size distributions (3–400 nm) were measured for three weeks both indoors and outdoors in a family house with natural ventilation in Espoo, Finland. We investigated the indoor-to-outdoor relationship of aerosol particles and analyzed the effects of indoor activities on the particle number size distributions. We also estimated the decay rate of indoor aerosol particle number concentrations. As expected, in the absence of indoor sources of aerosol particles the indoor particles originated from outdoors and the number concentrations followed similar patterns as those outdoors. The maximum penetration was found for particles between 100 and 400 nm in diameter. The mean value of the I/O values was 0.36 for ultrafine particles (UFP diameter <100 nm) and 0.60 for particles larger than 100 nm in diameter. Because of the penetration and deposition processes of aerosol particles, the modal structure of indoor particle number size distributions had larger geometric mean diameters and significantly lower number concentrations of UFP than those outdoors. The natural ventilation did not provide a stable and controlled indoor-to-outdoor relationship of aerosol particles and it caused variable I/O values and time-lags (10–45 min). In the presence of indoor activities, the indoor particle number concentrations cannot be directly estimated from the outdoor number concentrations only. The loss rate of UFP in the indoor air ranged from 1 h−1 for 10 nm particles to 0.1 h−1 for 100 nm particles in diameter. The quantitative and qualitative results presented in the current study are building and condition specific. However, the results provide a better understanding of the particle number size distribution characterizations indoors, especially during different indoor activities.
Measurements of particle number size distribution in the range 11–452 nm have been made on the side of the busy Marylebone Road in central London over a period from April 1998 to August 2001. The data have been analysed to demonstrate the influences of meteorological factors upon different size fractions and upon the overall size distribution. The relationship to traffic volumes indicates that the accumulation mode particles are associated with emissions from heavy-duty traffic (mainly diesel vehicles) whilst particles in the range 30–60 nm show a stronger association with light-duty traffic. Both of these size fractions show the anticipated dilution effect with increasing wind speed. Particles in the 11–30 nm range behave anomalously showing no clear relationships to traffic volumes and a lesser effect of dilution by increasing wind speed than for the larger particles. Particles in this fraction tend to peak in the early morning showing an inverse association with air temperature. It is concluded that this size range contains freshly nucleated particles formed as the exhaust gases are diluted with ambient air.
Characterization and emission rates of indoor aerosols have been of great interest. However, few studies have presented quantitative determinations of aerosol particle emissions during indoor activities. In the current study we presented and investigated the physical characteristics and size-fractionated emission rates of indoor aerosol particles during different activities in a house (naturally ventilated) located in Prague, Czech Republic. We utilized a multi-compartment and size-resolved indoor aerosol model (MC-SIAM) to investigate the indoor-to-outdoor relationship of aerosol particles and also to estimate their emission rates. When the windows and the main door were closed for several hours and there were minor indoor activities that did not produce significant amounts of aerosol particles, the particle number concentration showed similar levels at different indoor locations. As expected, the natural ventilation did not provide a controlled indoor-to-outdoor relationship of aerosol particles. As previous studies have emphasized, cooking and tobacco smoking activities are major sources indoors; the total particle number concentration was, respectively, as high as 1.8×105 and 3.6×104 cm−3 with emission rates around 380 and 36 cm−3 s−1. During intensive cooking activities the outdoor aerosol particle concentrations were also affected even though windows were closed. It seems that a simple model is not able to describe the fate of indoor aerosols within a multi-compartment construction; instead, a numerical and dynamic model with a multi-compartment approach is needed. Based on the indoor aerosol model simulations, the deposition rate was comparable to previous studies with friction velocity between 10–30 cm s−1 and surface area to volume ratio around 2.9–3.1 m−1. The penetration factor was equivalent to G3 filter standards and the ventilation rate varied between 0.6–1.2 h−1. Based on the emission rate analysis, aerosol particles produced during tobacco smoking and incense stick burning remain airborne for a longer time than cooking particles. It seems that aerosol particles emitted during tobacco smoking and incense stick burning undergo different processes; therefore, there is a need for a combined physical–chemical indoor aerosol model to better describe the evolution of indoor aerosol particles due to different activities.
Although recent studies have shown a positive association of exposure to ultrafine particulate matter (PM) with adverse effects on human health, it is not yet clear which PM components or properties of these particles may cause these responses. In the context of human exposure, depending on ventilation and air exchange ratios and in the absence of major indoor sources, an appreciable fraction of the indoor ultrafine aerosol is of outdoor origin. This study examined volatility of penetrating ultrafine outdoor particles, predominantly from freeway emissions, into indoor environments where other particle sources were minimized and no cooking activities took place. A tandem differential mobility analyzer (TDMA) system was used to study particle volatility at two apartments, 15 and 40 m downwind of the I-405 Freeway in Los Angeles, CA. The first differential mobility analyzer (DMA) selected particles of a certain diameter and subsequent heating of this monodisperse aerosol allowed for detection of changes in particle diameters by measuring the resulting size distribution with a second DMA. Aerosol volatility was examined by measuring changes in particle diameters as well as volume and number concentrations. Results suggest that outdoor particles are more volatile than indoor aerosols. Increasing temperature from ambient to decreased and broadened indoor and outdoor aerosol mode diameters, however greater mode decreases were observed for outdoor particles. Furthermore, outdoor particles lost more of their volume upon heating than indoor aerosols. No significant particle losses due to volatilization were observed at for either indoor or outdoor aerosols. A greater number of outdoor than indoor particles was lost at . Heated outdoor particles with diameters greater than 45 nm showed bi-modal distributions, indicating that some of the aerosol is composed of primarily non-volatile particles, whereas the remaining particles are composed of mainly volatile material and consequently shrink. Evaluation of outdoor particle volatility as a function of distance to the freeway revealed that aerosol volatility decreases with increasing distance from the source.
This study examines the evolution of the size distribution and mixing state of soot and background particles near a point and line source of emission. This evolution occurs invariably at a spatial scale smaller than that of the grid scale of urban through global atmospheric models, and the evolved distribution is that which is properly the source distribution “emitted” into such models. A recent set of field data showed that, within minutes of emission, the soot particle size distribution evolved substantially, and it was hypothesized that Brownian coagulation was the main cause of the evolution. Here, it is found that Brownian coagulation, alone, may be insufficient to account for the observed rapid evolution of the size distribution. Enhancement of Brownian coagulation due to van der Waals forces offset by viscous forces and fractal geometry may account for a greater share of the evolution. These coagulation processes are represented together with aerosol emissions, nucleation, condensation, dissolution, hydration, and chemistry among 10 aerosol classes in a high-resolution three-dimensional numerical simulation. Dilution is found to be more important than coagulation at reducing the total number concentration of particles near the source of emission, but the relative importance of dilution versus coagulation varies with concentration. It is also found that heterocoagulation of emitted soot with background particles produces new mixtures in increasing concentration with increasing distance from the emission source. However, self-coagulation of emitted soot reduces particle number concentration by an order of magnitude more than does heterocoagulation of emitted soot with background particles in the first few minutes after emission. Heterocoagulation increases in relative importance as emitted particles age.
High concentrations of ultrafine particles have been reported to exist near major freeways. Many urban residences are located in close proximity to high-density roadways. Consequently, indoor environments near freeways may experience significant concentrations of outdoor ultrafine particles. Given that people spend over 80% of their time indoors, understanding transport of ultrafine particles from outdoor to indoor environments is important for assessing the impact of exposure to outdoor particulate matter on human health. Four two-bedroom apartments within 60 m from the center of the 405 Freeway in Los Angeles, CA were used for this study. Indoor and outdoor ultrafine particle size distributions in the size range of 6–220 nm were measured concurrently under different ventilation conditions without indoor aerosol generation sources. The size distributions of indoor aerosols showed less variability than the adjacent outdoor aerosols. Indoor to outdoor ratios for ultrafine particle number concentrations depended strongly on particle size. Indoor/outdoor (I/O) ratios also showed dependence on the nature of indoor ventilation mechanisms. Under infiltration conditions with air exchange rates ranging from 0.31 to 1.11 h-1, the highest I/O ratios (0.6–0.9) were usually found for larger ultrafine particles (70–100 nm), while the lowest I/O ratios (0.1–0.4) were observed for particulate matter of 10–20 nm. Data collected under infiltration conditions were fitted into a dynamic mass balance model. Size-specific penetration factors and deposition rates were determined for all studied residences. Results from this research have implications concerning personal exposure to freeway-related ultrafine particles and possible associated health consequences.
Most of the particle number emitted by engines is in the nanoparticle range, Dp<50 nm, while most of the mass is in the accumulation mode, nm, range. Nanoparticles are typically hydrocarbons or sulfate and form by nucleation during dilution and cooling of the exhaust, while accumulation mode particles are mainly carbonaceous soot agglomerates formed directly by combustion. Emission standards on diesel engines have led to dramatic reductions in particle mass emitted. However, a new HEI study shows that some low-emission diesel engines emit much higher concentrations of nanoparticles than older designs and other low-emission designs. Many recent studies suggest that at similar mass concentrations; nanometer size particles are more dangerous than micron size particles. This has raised questions about whether nanoparticle (number based) emission standards should be imposed. Unlike mass, number is not conserved. It may change dramatically by nucleation and coagulation during dilution and sampling, making it very difficult to design a standard. Furthermore, if nanoparticles are a problem, spark ignition engines may also have to be controlled.
The ‘road-to-ambient’ evolution of particle number distributions near the 405 and 710 freeways in Los Angeles, California, in both summer and winter, were analyzed and then simulated by a multi-component sectional aerosol dynamic model. Condensation/evaporation and dilution were demonstrated to be the major mechanisms in altering aerosol size distribution, while coagulation and deposition play minor roles. Seasonal effects were significant with winters generally less dynamic than summers. A large number of particles grew into the >10 nm range around 30–90 m downwind of the freeways. Beyond 90 m some shrink to <10 nm range and some continued growing to >100 nm as a result of competition between partial pressure and vapor pressure. Particle compositions probably change dramatically as components adapt to decreasing gas-phase concentration due to dilution, so number distribution evolution is also an evolution of composition. As a result, people who live within about 90 m of roadways are exposed to particle sizes and compositions that others are not.
A recent solution to Brownian coagulation in a field of force (M.G. Sceats, J. Chem. Phys.84, 5206 (1986)) is applied over the entire range of relative particle size for neutral particles interacting through dispersion forces at arbitrary bath gas density. The long range forces manifest themselves through two stability factors W(0) and W(∞), which are readily evaluated for any interaction potential.
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Particle number concentration data have been collected on a very busy road in central London (Marylebone Road). Continuous size distributions from 15 nm to 10 μm diameter, collected over 21 days, were analyzed using positive matrix factorization which identified 10 factors, five of which were observed to make major contributions (greater than 8%) to either the total number or volume of particulate matter. The sources associated with each factor were identified from the size distribution, directional association, diurnal variation and their relationship to meteorological pollution and traffic volume variables. The factors related to the emissions on Marylebone Road accounted for 40.5% of particle volume and 71.9% of particle number. These comprised nucleation mode exhaust particles (3.6% of total volume and 27.4% of total number), solid mode exhaust particles (18.8% of total volume and 38.0% of total number), brake dust (13.7% of total volume and 1.7% of total number and resuspension (4.4% of total volume and 4.8% of total number). Another six factors were associated with the urban background accounting for 59.5% of total volume and 28.2% of total particle number count. The method is extremely successful at separating the components of on-road emissions including brake wear and resuspension.
The current study investigates the association of estimated personal exposure to traffic-related air pollution and acute myocardial infarction (AMI). Cases of AMI were interviewed in the Augsburg KORA Myocardial Infarction Registry from February 1999 through December 2003, and 960 AMI survivors were included in the analyses. The time-varying component of daily personal soot exposure (the temporally variable contribution due to the daily area level of exposure and daily personal activities) was estimated using a linear combination of estimated mean ambient soot concentration, time spent outdoors, and time spent in traffic. The association of soot exposure with AMI onset was estimated in a case-crossover analysis controlling for temperature and day of the week using conditional logistic regression analyses. Estimated personal soot exposure was associated with AMI (relative risk, 1.30 per 1.1 m(-1) × 10(-5) [95% confidence interval, 1.09-1.55]). Estimated ambient soot and measured ambient PM(2.5) particulate matter 2.5 µm and smaller in aerodynamic diameter were not significantly associated with AMI onset. Our results suggest that an increase in risk of AMI in association with personal soot exposure may be in great part due to the contribution of personal soot from individual times spent in traffic and individual times spent outdoors. As a consequence, estimates calculated based on measurements at urban background stations may be underestimations. Health effects of traffic-related air pollution may need to be updated, taking into account individual time spent in traffic and outdoors, to adequately protect the public.
We examined whether more precise exposure measures would better detect associations between traffic-related pollution, elemental carbon (EC), nitrogen dioxide (NO2), and heart rate variability (HRV).
Repeated 24-hour personal and ambient PM2.5, EC, and NO2 were measured for 30 people living in Atlanta, GA. The association between HRV and either ambient concentrations or personal exposures was examined using linear mixed effects models.
Ambient PM2.5, EC, NO2, and personal PM2.5 were not associated with HRV. Personal EC and NO2 measured 24 hours before HRV were associated with decreased RMSSD, PNN50, and HF and with increased LF/HF. RMSSD decreased by 10.97% (95% confidence interval: -18.00 to -3.34) for an inter-quartile range change in personal EC (0.81 microg/m3).
Results indicate decreased vagal tone in response to traffic pollutants, which can best be detected with precise personal exposure measures.
Animal studies have suggested that fine particulate matter (PM) can translocate from the upper respiratory tract to the brain and cause brain inflammation. Brain inflammation is involved in the pathogenesis of neurodegenerative diseases. Hypothesizing therefore that long-term exposure to fine PM might contribute to the development of Alzheimer's disease (AD), the objective of this study was to investigate the association between exposure to fine PM and mild cognitive impairment (MCI) which is associated with a high risk of progression to AD. A study group of 399 women aged 68-79 years who lived for more than 20 years at the same residential address has been assessed for long-term exposure to PM and tested for MCI. The exposure assessment comprised background concentration of PM(10) and traffic-related PM indicated by the distance of the residential address to the next busy road. The women were assessed for MCI by a battery of several neuropsychological tests and their odor identification ability. Consistent effects of traffic-related air pollution exposure on test performances including a dose-response relation were found. The associations were adjusted for potential confounders using regression analysis. These results indicate that chronic exposure to traffic-related PM may be involved in the pathogenesis of AD.
Because people spend approximately 85-90% of their time indoors, it is widely recognized that a significant portion of total personal exposures to ambient particles occurs in indoor environments. Although penetration efficiencies and deposition rates regulate indoor exposures to ambient particles, few data exist on the levels or variability of these infiltration parameters, in particular for time- and size-resolved data. To investigate ambient particle infiltration, a comprehensive particle characterization study was conducted in nine nonsmoking homes in the metropolitan Boston area. Continuous indoor and outdoor PM2.5 and size distribution measurements were made in each of the study homes over weeklong periods. Data for nighttime, nonsource periods were used to quantify infiltration factors for PM2.5 as well as for 17 discrete particle size intervals between 0.02 and 10 microns. Infiltration factors for PM2.5 exhibited large intra- and interhome variability, which was attributed to seasonal effects and home dynamics. As expected, minimum infiltration factors were observed for ultrafine and coarse particles. A physical-statistical model was used to estimate size-specific penetration efficiencies and deposition rates for these study homes. Our data show that the penetration efficiency depends on particle size as well as home characteristics. These results provide new insight on the protective role of the building shell in reducing indoor exposures to ambient particles, especially for tighter (e.g., winterized) homes and for particles with diameters greater than 1 micron.
A new explanation for the evolution of particles near a roadway is proposed. The explanation starts with data that suggest that small (<15 nm) liquid nanoparticles shed semivolatile organics (<C24) almost immediately upon emission. It is shown here that the shrinking of these particles enhances their rates of coagulation by over an order of magnitude, and this appears important in helping to explain particle evolution further downwind, as measured by two datasets, including one reported here, and as found with a three-dimensional numerical model used to simulate the data. Enhanced coagulation in isolated emission puffs may also affect evolution. Neither condensation, complete evaporation, coagulation alone, nor preferential small-particle dilution appears to explain the evolution.
Particle emissions from twelve buses, operating alternately on low sulfur (LS; 500 ppm) and ultralow sulfur (ULS; 50 ppm) diesel fuel, were monitored. The buses were 1-19 years old and had no after-treatment devices fitted. Measurements were carried out at four steady-state operational modes on a chassis dynamometer using a mini dilution tunnel (PM mass measurement) and a Dekati ejector diluter as a secondary diluter (SMPS particle number). The mean particle number emission rate (s(-1)) of the buses, in the size range 8-400 nm, using ULS diesel was 31% to 59% lower than the rate using LS diesel in all four modes. The fractional reduction was highest in the newest buses and decreased with mileage upto about 500,000 km, after which no further decrease was apparent. However, the mean total suspended particle (TSP) mass emission rate did not show a systematic difference between the two fuel types. When the fuel was changed from LS to ULS diesel, the reduction in particle number was mainly in the nanoparticle size range. Over all operational modes, 58% of the particles were smaller than 50 nm with LS fuel as opposed to just 45% with ULS fuel, suggesting that sulfur in diesel fuel was playing a major role in the formation of nanoparticles. The greatest influence of the fuel sulfur content was observed at the highest engine load, where 74% of the particles were smaller than 50 nm with LS diesel compared to 43% with ULS diesel.
Particulate air pollution (PM) is an important environmental health risk factor for many different diseases. This is indicated by numerous epidemiological studies on associations between PM exposure and occurrence of acute respiratory infections, lung cancer and chronic respiratory and cardiovascular diseases. The biological mechanisms behind these associations are not fully understood, but the results of in vitro toxicological research have shown that PM induces several types of adverse cellular effects, including cytotoxicity, mutagenicity, DNA damage and stimulation of proinflammatory cytokine production. Because traffic is an important source of PM emission, it seems obvious that traffic intensity has an important impact on both quantitative and qualitative aspects of ambient PM, including its chemical, physical and toxicological characteristics. In this review, the results are summarized of the most recent studies investigating physical and chemical characteristics of ambient and traffic-related PM in relation to its toxicological activity. This evaluation shows that, in general, the smaller PM size fractions (<PM(10)) have the highest toxicity, contain higher concentrations of extractable organic matter (comprising a wide spectrum of chemical substances), and possess a relatively high radical-generating capacity. Also, associations between chemical characteristics and PM toxicity tend to be stronger for the smaller PM size fractions. Most importantly, traffic intensity does not always explain local differences in PM toxicity, and these differences are not necessarily related to PM mass concentrations. This implies that PM regulatory strategies should take PM-size fractions smaller than PM(10) into account. Therefore, future research should aim at establishing the relationship between toxicity of these smaller fractions in relation to their specific sources.
A growing body of evidence indicates that residential proximity to traffic sources increases the risk for asthma and asthma exacerbations. In this review we have considered publications from 2006-2007 that examined the impact of residential traffic-related exposures on asthma occurrence and severity.
In these studies, exposures were estimated using traffic metrics based on residential distances from major roads and freeways, traffic densities around homes, and models of traffic exposure. Overall, residential proximity to traffic sources was associated with increased asthma occurrence and exacerbations in both children and adults. Land-use regression models were superior to individual traffic metrics in explaining the variability of traffic-related pollutants. Susceptibility may also play a role in variation in the effects of traffic on asthma.
There is consistent evidence that living near traffic sources is associated with asthma occurrence and exacerbations. Future studies have the opportunity to improve exposure estimates by measuring traffic-related pollutants near homes and schools and including time/activity patterns in prediction models. Further research is also warranted to investigate the differential impact of traffic by genetic and other susceptibility factors and to identify specific pollutants that underlie the adverse effect of traffic on asthma.
PMF analysis of wide-range particle size spectra collected on a major highway
- R M Harrison
- D C Beddows
- M Osto
Harrison, R. M., Beddows, D. C., Dall"Osto, M. (2011)PMF analysis of wide-range particle size
spectra collected on a major highway. Environ. Sci. Technol. 45:5522-5528.