-
[show abstract]
[hide abstract]
ABSTRACT: In this study we have provided simple analytical formulae to estimate the growth rate of a nucleation mode due to self-coagulation and the apparent growth rate due to coagulation scavenging by larger particles. These formulae were used on a set of simulations covering a wide range of atmospheric conditions. The modal growth rates were determined from the simulation results by summing the contribution of each process, by calculating the increase rate in the count mean diameter of the mode and by following the peak concentration of the mode. The results of these three methods were compared with each other and the means used to estimate the growth rate due to self-coagulation and coagulation scavenging were found to work quite well. We also investigated the role of charged particles and electric interactions in the growth of a nucleation mode. Charged particles were found to increase the growth rate due to both self-coagulation and coagulation scavenging by a factor of ~1.5 to 2. In case of increased condensation onto charged particles, the total condensational growth rate of a nucleation mode may increase significantly in the very early steps of the growth. The analytical formulae provided by this paper were designed to provide the growth rates due to different processes from aerosol dynamic simulations, but the same principles can be used to determine the growth rates from measurement data.
Atmospheric Chemistry and Physics Discussions. 01/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: Aerosol Optical Depth (AOD) and Ångström exponent (AE) values derived with the MODIS retrieval algorithm over land (Collection 5) are compared with ground based sun photometer measurements at eleven sites spanning the globe. Although, in general, total AOD compares well at these sites (R2 values generally over 0.8), there are cases (from 2 to 67% of the measurements depending on the site) where MODIS clearly retrieves the wrong spectral dependence, and hence, an unrealistic AE value. Some of these poor AE retrievals are due to the aerosol signal being too small (total AOD < 0.3) but in other cases the AOD should have been high enough to derive accurate AE. However, in these cases, MODIS indicates AE values close to 0.6 and zero fine model weighting (FMW), i.e. dust model provides the best fitting to the MODIS observed reflectance. Yet, according to evidence from the collocated sun photometer measurements and backtrajectory analyses, there should be no dust present. This indicates that the assumptions about aerosol model and surface properties made by the MODIS algorithm may have been incorrect. Here we focus on problems related to parameterization of the land-surface optical properties in the algorithm, in particular the relationship between the surface reflectance at 660 and 2130 nm. The retrieval assumes that there is a linear equation that relates the reflectance in these two channels, with the value of the slope (slope660/2130) determined, in part, by the infrared Normalized Difference Vegetation Index, (NDVISWIR). However, the assumed dependence of the slope on the NDVISWIR is not supported by a MODIS based surface albedo climatology. The use of a modified relationship based on the albedo data improves the AE retrieval at the studied sites. The increase in the AE agreement fraction between MODIS and AERONET measurements is between 3 and 22 percentage units depending on the site. These results indicate that the surface reflectance assumptions, especially the slope660/2130 in the MODIS algorithm is the major reason for the inaccurate AE values and the flawed aerosol model combining in the retrieval. However, at some of these sites, the new relationship slightly reduces the correlation between the MODIS and AERONET AOD. This decrease indicates that the combination of the assumed surface and aerosol properties still do not match the actual properties under investigation.
Atmospheric Measurement Techniques. 01/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: Atmospheric aerosols play a key role in the Earth's climate system by scattering and absorbing solar radiation and by acting as cloud condensation nuclei. Satellites are increasingly used to obtain information on properties of aerosol particles with a diam-eter larger than about 100 nm. However, new aerosol particles formed by nucleation 5 are initially much smaller and grow into the optically active size range on time scales of many hours. In this paper we derive proxies, based on process understanding and ground-based observations, to determine the concentrations of these new particles and their spatial distribution using satellite data. The results are applied to provide seasonal variation of nucleation mode concentration. The proxies describe the con-10 centration of nucleation mode particles over continents. The source rates are related to both regional nucleation and nucleation associated with primary emissions. The global pattern of nucleation mode particle number concentration predicted by satellite data using our proxies compares fairly well with both observations and global model simulations.
ACPD Chem. Phys. Discuss. 01/2011; 11(11):18823-18852.
-
S Mikkonen,
S Romakkaniemi,
J N Smith,
H Korhonen,
T Petaja,
C Plass-Duelmer,
M Boy,
P H McMurry, K E J Lehtinen,
J Joutsensaari,
A Hamed,
R L Mauldin III,
W Birmili,
G Spindler,
F Arnold,
M Kulmala,
A Laaksonen
[show abstract]
[hide abstract]
ABSTRACT: Gaseous sulphuric acid is a key precursor for new particle formation in the atmosphere. Previous experimental studies have confirmed a strong correlation between the number concentrations of freshly formed particles and the ambient concentrations of sulphuric acid. This study evaluates a body of experimental gas phase sulphuric acid concentrations, as measured by Chemical Ionization Mass Spectrometry (CIMS) during six intensive measurement campaigns and one long-term observational period. The campaign datasets were measured in Hyytiala, Finland, in 2003 and 2007, in San Pietro Capofiume, Italy, in 2009, in Melpitz, Germany, in 2008, in Atlanta, Georgia, USA, in 2002, and in Niwot Ridge, Colorado, USA, in 2007. The long term data were obtained in Hohenpeissenberg, Germany, during 1998 to 2000. The measured time series were used to construct proximity measures ("proxies") for sulphuric acid concentration by using statistical analysis methods. The objective of this study is to find a proxy for sulfuric acid that is valid in as many different atmospheric environments as possible. Our most accurate and universal formulation of the sulphuric acid concentration proxy uses global solar radiation, SO2 concentration, condensation sink and relative humidity as predictor variables, yielding a correlation measure (R) of 0.87 between observed concentration and the proxy predictions. Interestingly, the role of the condensation sink in the proxy was only minor, since similarly accurate proxies could be constructed with global solar radiation and SO2 concentration alone. This could be attributed to SO2 being an indicator for anthropogenic pollution, including particulate and gaseous emissions which represent sinks for the OH radical that, in turn, is needed for the formation of sulphuric acid.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2011; 11(21):11319-11334. · 5.52 Impact Factor
-
Hamed A,
Birmili W,
Joutsensaari J,
Mikkonen S,
Asmi A,
Wehner B,
Spindler G,
Jaatinen A,
Wiedensohler A,
Korhonen H, K. E. J. Lehtinen,
Laaksonen A
[show abstract]
[hide abstract]
ABSTRACT: In anthropogenically influenced atmospheres, sulphur dioxide (SO<sub>2</sub>) is the main precursor of gaseous sulphuric acid (H<sub>2</sub>SO<sub>4</sub>), which in turn is a main precursor for atmospheric particle nucleation. As a result of socio-economic changes, East Germany has seen a dramatic decrease in anthropogenic SO<sub>2</sub> emissions between 1989 and present, as documented by routine air quality measurements in many locations. We have attempted to evaluate the influence of changing SO<sub>2</sub> concentrations on the frequency and intensity of new particle formation (NPF) using two different data sets (1996–1997; 2003–2006) of experimental particle number size distributions (diameter range 3–750 nm) from the atmospheric research station Melpitz near Leipzig, Germany. Between the two periods SO<sub>2</sub> concentrations decreased by 65% on average, while the frequency of NPF events dropped by 45%. Meanwhile, the average formation rate of 3 nm particles decreased by 68% on average. The trends were statistically significant and therefore suggest a connection between the availability of anthropogenic SO<sub>2</sub> and freshly formed new particles. In contrast to the decrease in new particle formation, we found an increase in the mean growth rate of freshly nucleated particles (+22%), suggesting that particle nucleation and subsequent growth into larger sizes are delineated with respect to their precursor species. Using three basic parameters, the condensation sink for H<sub>2</sub>SO<sub>4</sub>, the SO<sub>2</sub> concentration, and the global radiation intensity, we were able to define the characteristic range of atmospheric conditions under which particle formation events take place at the Melpitz site. While the decrease in the concentrations and formation rates of the new particles was rather evident, no similar decrease was found with respect to the generation of cloud condensation nuclei (CCN; particle diameter >100 nm) as a result of atmospheric nucleation events. On the contrary, the production of CCN following nucleation events appears to have increased by tens of percents. Our aerosol dynamics model simulations suggest that such an increase can be caused by the increased particle growth rate.
Atmospheric Chemistry and Physics. 01/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: The growth of freshly formed nanoparticles has been investigated. A new analytical expression based on a recently developed exact solution for the condensational growth rate has been derived. Based on the new growth rate, a new approximate but accurate analytical expression for growth time has been derived. The expression includes transition regime effects on growth, molecule size effects on the collision cross section and particle mobility effects on the relative collisional speeds – the last two of which are typically neglected, but may have significant effects when dealing with the growth of freshly nucleated particles. To demonstrate the use of the derived expressions, the contribution of sulphuric acid and organic compounds on sub 3 nm and sub 10 nm particle growth rates has been studied. For sulphuric acid also the effect of hydration as function of relative humidity has been taken into account. According to the new expression the needed sulphuric acid concentration for 1 nm/h growth in sub 3 nm range is ca. 7×106 cm−3, which is a factor of two smaller than values typically used in aerosol physics based on standard model in kinetic regime.
Atmospheric Chemistry and Physics Discussions. 01/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: The aim of this work was to develop a model ideally suited for detailed studies on aerosol dynamics, gas and particle phase chemistry within urban plumes, from local scale (1×1 km2) to regional or global scale. This article describes and evaluates the trajectory model for Aerosol Dynamics, gas and particle phase CHEMistry and radiative transfer (ADCHEM), which has been developed and used at Lund University since 2007. The model treats both vertical and horizontal dispersion perpendicular to an air mass trajectory (2-space dimensions), which is not treated in Lagrangian box-models (0-space dimensions). The Lagrangian approach enables a more detailed representation of the aerosol dynamics, gas and particle phase chemistry and a finer spatial and temporal resolution compared to that of available regional 3D-CTMs. These features make it among others ideally suited for urban plume studies. The aerosol dynamics model includes Brownian coagulation, dry deposition, wet deposition, in-cloud processing, condensation, evaporation, primary particle emissions and homogeneous nucleation. The gas phase chemistry model calculates the gas phase concentrations of 63 different species, using 119 different chemical reactions. Daily isoprene and monoterpene emissions from European forests were simulated separately with the vegetation model LPJ-GUESS, and included as input to ADCHEM. ADCHEM was used to simulate the ageing of the urban plumes from the city of Malmö in Southern Sweden (280 000 inhabitants). Several sensitivity tests were performed concerning the number of size bins, size structure method, coupled or uncoupled condensation, the volatility basis set (VBS) or traditional 2-product model for secondary organic aerosol formation, different aerosol dynamic processes and vertical and horizontal mixing. The simulations show that the full-stationary size structure gives accurate results with little numerical diffusion when more than 50 size bins are used between 1.5 and 2500 nm, while the moving-center method is preferable when only a few size bins are selected. The particle number size distribution in the center of the urban plume from Malmö is mainly affected by dry deposition, coagulation and condensation, and is relatively insensitive to moderate variations in the vertical and horizontal mixing, as long as the mixing height is relatively uniform. The modeled PM2.5 was dominated by organics, nitrate, sulfate and ammonium. If treating the condensation of HNO3 and NH3 as a coupled process (pH independent) the model gave lower nitrate PM2.5 values than if considering uncoupled condensation. However, both methods gave similar and significant temporal variation in the particulate nitrate content, primarily due to fluctuation in the relative humidity.
Atmospheric Chemistry and Physics Discussions. 01/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: Different methods of determining formation rates of 3 nm particles are compared, basing on analysis of simulated data, but the results are valid for analyses of experimental particle size distribution data as well. The study shows that the method of determining formation rates indirectly from measured number concentration data of 3–6 nm particles is generally in good agreement with the theoretical calculation with a systematic error of 0–20%. While this is often accurate enough, a simple modification to the approximative equation for the formation rate is recommended. Additionally, the temporal connection between the concentration of the nucleating vapour and the formation rate is studied. It is concluded that the often used power-law connecting these two is inaccurate.
Atmospheric Chemistry and Physics Discussions. 01/2010;
-
Mikkonen S,
Korhonen H,
Romakkaniemi S,
J. N. Smith,
Joutsensaari J, K. E. J. Lehtinen,
Hamed A,
T. J. Breider,
Birmili W,
Spindler G,
Plass-Duelmer C,
M. C. Facchini,
Laaksonen A
[show abstract]
[hide abstract]
ABSTRACT: Measurements of aerosol size-distribution and different gas and meteorological parameters, made in three polluted sites in Central- and Southern Europe: Po Valley, Italy, Melpitz and Hohenpeissenberg in Germany, were analysed for this study to examine which of the meteorological and trace gas variables affect the number concentration of Aitken (Dp=50 nm) particles. The aim of our study was to predict the number concentration of 50 nm particles by a combination of in-situ meteorological and gas phase parameters. The statistical model needs to describe, amongst others, the factors affecting the growth of newly formed aerosol particles (below 10 nm) to 50 nm size, but also sources of direct particle emissions in that size range. As the analysis method we used multivariate nonlinear mixed effects model. Hourly averages of gas and meteorological parameters measured at the stations were used as predictor variables; the best predictive model was attained with a combination of relative humidity, new particle formation event probability, temperature, condensation sink and concentrations of SO2, NO2 and ozone. The seasonal variation was also taken into account in the mixed model structure. Model simulations with the Global Model of Aerosol Processes (GLOMAP) indicate that the parameterization can be used as a part of a larger atmospheric model to predict the concentration of climatically active particles. As an additional benefit, the introduced model framework is, in theory, applicable for any kind of measured aerosol parameter.
Geoscientific Model Development Discussions. 01/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: The growth of freshly formed nanoparticles has been investigated. A new analytical expression based on a recently developed exact solution for the condensational growth rate has been derived. Based on the new growth rate, a new approximate but accurate analytical expression for growth time has been derived. The expression includes transition regime effects on growth, molecule size effects on the collision cross section and particle thermal speed effects on the relative collisional speeds – the last two of which are typically neglected, but may have significant effects when dealing with the growth of freshly nucleated particles. To demonstrate the use of the derived expressions, the contribution of sulphuric acid and organic compounds on sub 3 nm and sub 10 nm particle growth rates has been studied. For sulphuric acid also the effect of hydration as function of relative humidity has been taken into account. According to the new expression the sulphuric acid concentration needed for 1 nm/h growth in sub 3 nm range is ca. 1.5×107 cm−3, which is a factor of 1.5 smaller than values typically used in aerosol physics based on standard model in kinetic regime.
Atmospheric Chemistry and Physics. 01/2010;
-
Kerminen V.-M,
Petäjä T,
H. E. Manninen,
Paasonen P,
Nieminen T,
Sipilä M,
Junninen H,
Ehn M,
Gagné S,
Laakso L, [......],
T. F. Mentel,
Wildt J,
P. M. Winkler,
P. E. Wagner,
Petzold A,
Minikin A,
Plass-Dülmer C,
Pöschl U,
Laaksonen A,
Kulmala M
[show abstract]
[hide abstract]
ABSTRACT: Within the project EUCAARI (European Integrated project on Aerosol Cloud Climate and Air Quality interactions), atmospheric nucleation was studied by (i) developing and testing new air ion and cluster spectrometers, (ii) conducting homogeneous nucleation experiments for sulphate and organic systems in the laboratory, (iii) investigating atmospheric nucleation mechanism under field conditions, and (iv) applying new theoretical and modelling tools for data interpretation and development of parameterisations. The current paper provides a synthesis of the obtained results and identifies the remaining major knowledge gaps related to atmospheric nucleation. The most important technical achievement of the project was the development of new instruments for measuring sub-3 nm particle populations, along with the extensive application of these instruments in both the laboratory and the field. All the results obtained during EUCAARI indicate that sulphuric acid plays a central role in atmospheric nucleation. However, also vapours other than sulphuric acid are needed to explain the nucleation and the subsequent growth processes, at least in continental boundary layers. Candidate vapours in this respect are some organic compounds, ammonia, and especially amines. Both our field and laboratory data demonstrate that the nucleation rate scales to the first or second power of the nucleating vapour concentration(s). This agrees with the few earlier field observations, but is in stark contrast with classical thermodynamic nucleation theories. The average formation rates of 2-nm particles were found to vary by almost two orders of magnitude between the different EUCAARI sites, whereas the formation rates of charged 2-nm particles varied very little between the sites. Overall, our observations are indicative of frequent, yet moderate, ion-induced nucleation usually outweighed by much stronger neutral nucleation events in the continental lower troposphere. The most concrete outcome of the EUCAARI nucleation studies are the new semi-empirical nucleation rate parameterizations based on field observations, along with updated aerosol formation parameterizations.
Atmospheric Chemistry and Physics. 01/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: Several mathematical tools have been developed in recent years to analyze new particle formation rates and to estimate nucleation rates and mechanisms at sub-3nm sizes from atmospheric aerosol data. Here we evaluate these analysis tools using 1239 numerical nucleation events for which the nucleation mechanism and formation rates were known exactly. The accuracy of the estimates of particle formation rate at 3 nm (J3) showed significant sensitivity to the details of the analysis, i.e. form of equations used and assumptions made about the initial size of nucleating clusters, with the fraction of events within a factor-of-two accuracy ranging from 43–97%. In general, the estimates of the actual nucleation rate at 1.5 nm (J1.5) were less accurate, and even the most accurate analysis set-up estimated only 59% of the events within a factor of two of the simulated mean nucleation rate. The J1.5 estimates were deteriorated mainly by the size dependence of the cluster growth rate below 3 nm, which the analysis tools do not take into account, but also by possible erroneous assumptions about the initial cluster size. The poor estimates of J1.5 can lead to large uncertainties in the nucleation prefactors (i.e. constant P in nucleation equation J1.5 = P × [H2SO4]k). Large uncertainties were found also in the procedures that are used to determine the nucleation mechanism. When applied to individual events, the analysis tools clearly overestimated the number of H2SO4 molecules in a critical cluster for most events, and thus associated them with a wrong nucleation mechanism. However, in some conditions the number of H2SO4 molecules in a critical cluster was underestimated. This indicates that analysis of field data that implies a maximum of 2 H2SO4 molecules in a cluster does not automatically rule out a higher number of molecules in the actual nucleating cluster. Our analysis also suggests that combining data from several new particle formation events to scatter plots of H2SO4 vs. formation rates (J1.5 or J3) and determining the slope of the regression line may not give reliable information about the nucleation mechanism.
Atmospheric Chemistry and Physics Discussions. 01/2010;
-
Komppula M,
Mielonen T,
Arola A,
Korhonen K,
Lihavainen H,
Hyvärinen A.-P,
Baars H,
Engelmann R,
Althausen D,
Ansmann A,
Müller D,
T. S. Panwar,
R. K. Hooda,
V. P. Sharma,
Kerminen V.-M, K. E. J. Lehtinen,
Viisanen Y
[show abstract]
[hide abstract]
ABSTRACT: One year of multi-wavelength (3+2) Raman lidar measurements at Gual Pahari, close to Delhi, were analysed. The data was split into four seasons: spring (March–May), summer (June–August), autumn (September–November) and winter (December–February). The vertical profiles of backscatter, extinction, and lidar ratio and their variability during each season are presented. The measurements revealed that, on average, the aerosol layer was at its highest in spring (5.5 km). In summer, the vertically averaged (between 1–3 km) backscatter and extinction coefficients had the highest averages (3.3 Mm−1 sr−1 and 142 Mm−1 at 532 nm, respectively). Aerosol concentrations were slightly higher in summer compared with other seasons, and particles were larger in size. The autumn showed the highest lidar ratio and high extinction-related Ångström exponents (AEext), indicating the presence of smaller probably absorbing particles. The winter had the lowest backscatter and extinction coefficients, but AEext was the highest, suggesting still a large amount of small particles.
Atmospheric Chemistry and Physics Discussions. 01/2010;
-
Hamed A,
Birmili W,
Joutsensaari J,
Mikkonen S,
Asmi A,
Wehner B,
Spindler G,
Jaatinen A,
Uhse K,
Wiedensohler A, K. E. J. Lehtinen,
Laaksonen A
[show abstract]
[hide abstract]
ABSTRACT: In anthropogenically influenced atmospheres, sulphur dioxide (SO2) is the main precursor of gaseous sulphuric acid (H2SO4), which in turn forms new aerosol particles (diameter 2 emissions between 1989 and present, as documented by routine air quality measurements in many locations. Using two different data sets of experimental particle number size distributions (3–750 nm) from the research station Melpitz (1996–1997 and 2003–2006) we have attempted to evaluate the possible influence of changing SO2 concentrations on the frequency and intensity of new particle formation (NPF). Between the two periods SO2 concentrations decreased on average by 65%, while the frequency of NPF events dropped by 45%. In addition, the average formation rate of 3 nm particles decreased by 68%. The trends were statistically significant, therefore suggesting a connection between the availability of anthropogenic SO2 and the production of new particle number. A contrasting finding was the increase in the mean growth rate of freshly nucleated particles (+22%), suggesting that particle nucleation and subsequent growth into larger sizes are delineated with respect to their precursor species. Using three basic parameters, the condensation sink for H2SO4, the SO2 concentration, and global radiation intensity, we could define the characteristic range of atmospheric conditions under which particle formation events at the Melpitz site take place or not. While the connection between anthropogenic SO2, H2SO4 and NPF appears very plausible, our analysis yielded no significant evidence whether decreasing SO2 concentrations did affect the production of cloud condensation nuclei (CCN).
Atmospheric Chemistry and Physics Discussions. 01/2009;
-
A Laaksonen,
M Kulmala,
C D O 'dowd,
J Joutsensaari,
P Vaattovaara,
S Mikkonen, K E J Lehtinen,
L Sogacheva,
M Dal Maso,
P Aalto, [......],
K Sellegri,
B Umann,
W Junkermann,
H Coe,
J D Allan,
M R Alfarra,
D R Worsnop,
M.-L Riekkola,
T Hyötyläinen,
Y Viisanen
[show abstract]
[hide abstract]
ABSTRACT: Aerosol physical and chemical properties and trace gas concentrations were measured during the QUEST field campaign in March–April 2003, in Hyytiälä, Finland. Our aim was to understand the role of oxidation products of VOC's such as mono-and sesquiterpenes in atmospheric nu-cleation events. Particle chemical compositions were mea-sured using the Aerodyne Aerosol Mass Spectrometer, and chemical compositions of aerosol samples collected with low-pressure impactors and a high volume sampler were analysed using a number of techniques. The results indi-cate that during and after new particle formation, all parti-Correspondence to: A. Laaksonen (ari.laaksonen@uku.fi) cles larger than 50 nm in diameter contained similar organic substances that are likely to be mono-and sesquiterpene ox-idation products. The oxidation products identified in the high volume samples were shown to be mostly aldehydes. In order to study the composition of particles in the 10–50 nm range, we made use of Tandem Differential Mobility Ana-lyzer results. We found that during nucleation events, both 10 and 50 nm particle growth factors due to uptake of ethanol vapour correlate strongly with gas-phase monoterpene oxi-dation product (MTOP) concentrations, indicating that the organic constituents of particles smaller than 50 nm in di-ameter are at least partly similar to those of larger particles. We furthermore showed that particle growth rates during the nucleation events are correlated with the gas-phase MTOP Published by Copernicus Publications on behalf of the European Geosciences Union. 2658 A. Laaksonen et al.: VOC oxidation products and new particle formation concentrations. This indicates that VOC oxidation products may have a key role in determining the spatial and temporal features of the nucleation events. This conclusion was sup-ported by our aircraft measurements of new 3–10 nm particle concentrations, which showed that the nucleation event on 28 March 2003, started at the ground layer, i.e. near the VOC source, and evolved together with the mixed layer. Further-more, no new particle formation was detected upwind away from the forest, above the frozen Gulf of Bothnia.
Atmospheric Chemistry and Physics 07/2008; 8:2657-2665.
-
Kokkola H,
Korhonen H, K. E. J. Lehtinen,
Makkonen R,
Asmi A,
Järvenoja S,
Anttila T,
Partanen A.-I,
Kulmala M,
Järvinen H,
Laaksonen A,
Kerminen V.-M
[show abstract]
[hide abstract]
ABSTRACT: The sectional aerosol module SALSA is introduced. The model has been designed to be implemented in large scale climate models, which require both accuracy and computational efficiency. We have used multiple methods to reduce the computational burden of different aerosol processes to optimize the model performance without losing physical features relevant to problematics of climate importance. The optimizations include limiting the chemical compounds and physical processes available in different size sections of aerosol particles; division of the size distribution into size sections using size sections of variable width depending on the sensitivity of microphysical processing to the particles sizes; the total amount of size sections to describe the size distribution is kept to the minimum; furthermore, only the relevant microphysical processes affecting each size section are calculated. The ability of the module to describe different microphysical processes was evaluated against explicit microphysical models and several microphysical models used in air quality models. The results from the current module show good consistency when compared to more explicit models. Also, the module was used to simulate a new particle formation event typical in highly polluted conditions with comparable results to more explicit model setup.
Atmospheric Chemistry and Physics. 01/2008;
-
[show abstract]
[hide abstract]
ABSTRACT: We have performed a series of simulations with an aerosol dynamics box model to study the connection between new particle formation and sulphuric acid concentration. For nucleation either activation mechanism with a linear dependence on the sulphuric acid concentration or ternary H2O-H2SO4-NH3 nucleation was assumed. We investigated the factors that affect the sulphuric acid dependence during the early stages of particle growth, and tried to find conditions which would yield the linear dependence between the particle number concentration at 3–6 nm and sulphuric acid, as observed in field experiments. The simulations showed that the correlation with sulphuric acid may change during the growth from nucleation size to 3–6 nm size range, the main reason being the size dependent growth rate between 1 and 3 nm. In addition, the assumed size for the nucleated clusters had a crucial impact on the sulphuric acid dependence at 3 nm. The simulations yielded a linear dependence between the particle number concentration at 3 nm and sulphuric acid, when a low saturation vapour pressure for the condensable organic vapour was assumed, or when nucleation took place at ~2 nm instead of ~1 nm. Comparison of results with activation and ternary nucleation showed that ternary nucleation cannot explain the experimentally observed linear or square dependence on sulphuric acid.
Atmospheric Chemistry and Physics Discussions. 01/2008;
-
Hamed A,
Joutsensaari J,
Mikkonen S,
Sogacheva L,
M. Dal Maso,
Kulmala M,
Cavalli F,
Fuzzi S,
M. C. Facchini,
Decesari S,
Mircea M, K. E. J. Lehtinen,
Laaksonen A
[show abstract]
[hide abstract]
ABSTRACT: Aerosol number distribution measurements are reported at San Pietro Capofiume (SPC) station (44°39' N, 11°37' E) for the time period 2002–2005. The station is located in Po Valley, the largest industrial, trading and agricultural area in Italy with a high population density. New particle formation was studied based on observations of the particle size distribution, meteorological and gas phase parameters. The nucleation events were classified according to the event clarity based on the particle number concentrations, and the particle formation and growth rates. Out of a total of 769 operational days from 2002 to 2005 clear events were detected on 36% of the days whilst 33% are clearly non-event days. The event frequency was high during spring and summer months with maximum values in May and July, whereas lower frequency was observed in winter and autumn months. The average particle formation and growth rates were estimated as ~6 cm<sup>−3</sup> s<sup>−1</sup> and ~7 nm h<sup>−1</sup>, respectively. Such high growth and formation rates are typical for polluted areas. Temperature, wind speed, solar radiation, SO<sub>2</sub> and O<sub>3</sub> concentrations were on average higher on nucleation days than on non-event days, whereas relative and absolute humidity and NO<sub>2</sub> concentration were lower; however, seasonal differences were observed. Backtrajectory analysis suggests that during majority of nucleation event days, the air masses originate from northern to eastern directions. We also study previously developed nucleation event correlations with environmental variables and show that they predict Po Valley nucleation events with variable success.
Atmospheric Chemistry and Physics. 01/2007;
-
Laaksonen A,
Kulmala M,
C. D. O&apos,
Dowd,
Joutsensaari J,
Vaattovaara P,
Mikkonen S, K. E. J. Lehtinen,
Sogacheva L,
M. Dal Maso, [......],
Sellegri K,
Umann B,
Junkermann W,
Coe H,
J. D. Allan,
M. Rami Alfarra,
D. R. Worsnop,
Riekkola M.-L,
Hyötyläinen T,
Viisanen Y
[show abstract]
[hide abstract]
ABSTRACT: Aerosol physical and chemical properties and trace gas concentrations were measured during the QUEST field campaign in March–April, 2003, in Hyytiälä, Finland. Our aim was to understand the role of oxidation products of VOC's such as mono- and sesquiterpenes in atmospheric nucleation events. Particle chemical compositions were measured using the Aerodyne Aerosol Mass Spectrometer, and chemical compositions of aerosol samples collected with low-pressure impactors and a high volume sampler were analysed using a number of techniques. The results indicate that during and after new particle formation, all particles larger than 50 nm in diameter contained similar organic substances that are likely to be mono- and sesquiterpene oxidation products. The oxidation products identified in the high volume samples were shown to be mostly aldehydes. In order to study the composition of particles in the 10–50 nm range, we made use of Tandem Differential Mobility Analyzer results. We found that during nucleation events, both 10 and 50 nm particle growth factors due to uptake of ethanol vapour correlate strongly with gas-phase monoterpene oxidation product (MTOP) concentrations, indicating that the organic constituents of particles smaller than 50 nm in diameter are at least partly similar to those of larger particles. We furthermore showed that particle growth rates during the nucleation events are correlated with the gas-phase MTOP concentrations. This indicates that VOC oxidation products may have a key role in determining the spatial and temporal features of the nucleation events. This conclusion was supported by our aircraft measurements of new 3–10 nm particle concentrations, which showed that the nucleation event on 28 March 2003, started at the ground layer, i.e. near the VOC source, and evolved together with the mixed layer. Furthermore, no new particle formation was detected upwind away from the forest, above the frozen Gulf of Bothnia.
Atmospheric Chemistry and Physics Discussions. 01/2007;
-
M. Kulmala,
I. Riipinen,
M. Sipilä,
H.E. Manninen,
T. Petäjä,
H. Junninen,
M. Dal Maso,
G. Mordas,
A. Mirme,
M. Vana,
A. Hirsikko,
L. Laakso,
R.M. Harrison,
I. Hanson,
C. Leung, K.E.J. Lehtinen,
V.-M. Kerminen
Science 01/2007; 318:89-92. · 31.20 Impact Factor
