[Show abstract][Hide abstract] ABSTRACT: Reactive oxygen species (ROS), such as free radicals and peroxides, are environmental trace pollutants potentially associated with asthma and airways inflammation. These compounds are often not detected in indoor air due to sampling and analytical limitations. This study developed and validated an experimental method to sample, identify and quantify ROS in indoor air using fluorescent probes. Tests were carried out simultaneously using three different probes: 2',7'-dichlorofluorescin (DCFH) to detect a broad range of ROS, Amplex ultra Red® (AuR) to detect peroxides, and terephthalic acid (TPA) to detect hydroxyl radicals (HO(•)). For each test, air samples were collected using two impingers in series kept in an ice bath, containing each 10mL of 50mM phosphate buffer at pH 7.2. In tests with TPA, that probe was also added to the buffer prior to sampling; in the other two tests, probes and additional reactants were added immediately after sampling. The concentration of fluorescent byproducts was determined fluorometrically. Calibration curves were developed by reacting DCFH and AuR with known amounts of H2O2, and using known amounts of 2-hydroxyterephthalic acid (HTPA) for TPA. Low detection limits (9-13nM) and quantification limits (18-22nM) were determined for all three probes, which presented a linear response in the range 10-500nM for AuR and TPA, and 100-2000nM for DCFH. High collection efficiency (CE) and recovery efficiency (RE) were observed for DCFH (CE=RE=100%) and AuR (CE=100%; RE=73%) by sampling from a laboratory-developed gas phase H2O2 generator. Interference of co-occurring ozone was evaluated and quantified for the three probes by sampling from the outlet of an ozone generator. The method was demonstrated by sampling air emitted by two portable air cleaners: a strong ozone generator (AC1) and a plasma generator (AC2). High ozone levels emitted by AC1 did not allow for simultaneous determination of ROS levels due to high background levels associated with ozone decomposition in the buffer. However, emitted ROS were quantified at the outlet of AC2 using two of the three probes. With AuR, the concentration of peroxides in air emitted by the air cleaner was 300ppt of H2O2 equivalents. With TPA, the HO(•) concentration was 47ppt. This method is best suited to quantify ROS in the presence of low ozone levels.
Published by Elsevier B.V.
[Show abstract][Hide abstract] ABSTRACT: For the first time, nitric oxide (NO), a precursor of nitrogen dioxide (NO2, a NIOSH-listed atmospheric pollutant), has been found to be one of the final products of the photocatalytic reduction of nitrate in water using TiO2 and formic acid as hole scavenger.
[Show abstract][Hide abstract] ABSTRACT: Thirdhand smoke (THS) is the complex mixture of cigarette smoke chemicals that linger in the environment after cigarettes are smoked. Research has shown that the majority of semi-volatile organic compounds released during smoking stick to indoor surfaces before they can be removed by ventilation. This “tar” can react with ambient air to create new chemicals, some of which are volatile and re-enter the air. To identify the volatile organic compounds (VOCs) released from THS-contaminated surfaces, we exposed paper, 100% cotton cloth and 100% polyester cloth to secondhand cigarette smoke. The materials were exposed in a stainless steel exposure chamber, for 163 hours over 110 days. After the exposure, half the samples were stored in amber glass vials at -20 C. The others were placed on a shelf in the laboratory and allowed to react and desorb or “air out” under ambient conditions for 42 days. Control samples were not exposed to smoke and were treated in parallel. The VOCs emitted by the samples were then identified and quantified using real-time proton-transfer reaction mass spectrometer (PTR-MS). Our results show that the samples emitted a broad spectrum of VOCs, including acetonitrile, furan, toluene, formaldehyde, acetaldehyde and acrolein. The samples that had desorbed for 42 days at room temperature still emitted VOCs at levels well above the control samples that had not been exposed to smoke. We conclude that THS may be a significant source of VOC exposures indoors and that VOC emissions from THS persist for months after the last cigarette.
142nd APHA Annual Meeting and Exposition 2014; 11/2014
[Show abstract][Hide abstract] ABSTRACT: Tobacco smoke residues lingering in the indoor environment, also referred to as thirdhand smoke (THS), can be a source of long-term exposure to harmful pollutants. THS composition is affected by chemical transformations and by air/surface partitioning over timescales of minutes to months. This study identified and quantified airborne THS pollutants available for respiratory exposure, identified potential environmental tracers, and estimated health impacts to non-smokers. In a ventilated 18-m3 laboratory chamber, six cigarettes were machine-smoked, and levels of particulate matter (PM2.5) and 58 volatile organic compounds (VOCs) were monitored during an aging period of 18 hours. Results were compared with field measurements carried out in a smoker's home 8 hours after the last cigarette was smoked. Initial chamber levels of individual VOCs in freshly emitted secondhand smoke (SHS) were in the range 1 - 300 μg m-3. The commonly used SHS tracers 3-ethenyl pyridine (3-EP) and nicotine were no longer present in the gas phase after 2 hours, likely due mostly to sorption to surfaces. By contrast, other VOCs persisted in the gas phase for at least 18 hours, particularly furans, carbonyls and nitriles. The concentration ratio of acetonitrile to 3-EP increased substantially with aging. This ratio may provide a useful metric to differentiate freshly emitted (SHS) from aged smoke (THS). Among the 29 VOCs detected in the smoker's home at moderate to high concentrations, 18 compounds were also detected in simultaneously sampled outdoor air, but acetonitrile, 2-methyl furan and 2,5-dimethyl furan appeared to be specific to cigarette smoke. Acrolein, methacrolein and acrylonitrile exceeded concentrations considered harmful by the State of California. An initial exposure and impact assessment was carried out for a subset of pollutants by computing disability-adjusted life years (DALYs) lost, using available toxicological and epidemiological information. Exposure to PM2.5 contributed to more than 90% of the predicted harm. Acrolein, furan, acrylonitrile and 1,3-butadiene were considered to be the most harmful VOCs. Depending on which criteria are used to establish the separation between SHS and THS, 5% to 60% of the predicted health damage could be attributed to THS exposure. Benefits and limitations of this approach are discussed.
[Show abstract][Hide abstract] ABSTRACT: To investigate the impacts of an energy efficiency retrofit, indoor air quality and resident health was evaluated at a low-income senior housing apartment complex in Phoenix, Arizona before and after a green energy building renovation. Indoor and outdoor air quality sampling was carried out simultaneously with a questionnaire to characterize personal habits and general health of residents. Measured indoor formaldehyde levels before the building retrofit routinely exceeded reference exposure limits, but in the long term follow-up sampling, indoor formaldehyde decreased for the entire study population by a statistically significant margin. Indoor PM levels were dominated by fine particles and showed a statistically significant decrease in the long term follow-up sampling within certain resident subpopulations (i.e. residents who report smoking and residents who had lived longer at the apartment complex). This article is protected by copyright. All rights reserved.
Indoor Air 06/2014; 25(2). DOI:10.1111/ina.12134 · 4.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Highly reflective roofs can decrease the energy required for building air conditioning, help mitigate the urban heat island effect, and slow global warming. However, these benefits are diminished by soiling and weathering processes that reduce the solar reflectance of most roofing materials. Soiling results from the deposition of atmospheric particulate matter and the growth of microorganisms, each of which absorb sunlight. Weathering of materials occurs with exposure to water, sunlight, and high temperatures. This study developed an accelerated aging method that incorporates features of soiling and weathering. The method sprays a calibrated aqueous soiling mixture of dust minerals, black carbon, humic acid, and salts onto preconditioned coupons of roofing materials, then subjects the soiled coupons to cycles of ultraviolet radiation, heat and water in a commercial weatherometer. Three soiling mixtures were optimized to reproduce the site-specific solar spectral reflectance features of roofing products exposed for 3 years in a hot and humid climate (Miami, Florida); a hot and dry climate (Phoenix, Arizona); and a polluted atmosphere in a temperate climate (Cleveland, Ohio). A fourth mixture was designed to reproduce the three-site average values of solar reflectance and thermal emittance attained after 3 years of natural exposure, which the Cool Roof Rating Council (CRRC) uses to rate roofing products sold in the US. This accelerated aging method was applied to 25 products–single ply membranes, factory and field applied coatings, tiles, modified bitumen cap sheets, and asphalt shingles–and reproduced in 3 days the CRRC's 3-year aged values of solar reflectance. This accelerated aging method can be used to speed the evaluation and rating of new cool roofing materials.
Solar Energy Materials and Solar Cells 03/2014; 122:271–281. DOI:10.1016/j.solmat.2013.11.028 · 5.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cigarette smoking remains a significant health threat for smokers and nonsmokers alike. Secondhand smoke (SHS) is intrinsically more toxic than directly inhaled smoke. Recently, a new threat has been discovered - Thirdhand smoke (THS) - the accumulation of SHS on surfaces that ages with time, becoming progressively more toxic. THS is a potential health threat to children, spouses of smokers and workers in environments where smoking is or has been allowed. The goal of this study is to investigate the effects of THS on liver, lung, skin healing, and behavior, using an animal model exposed to THS under conditions that mimic exposure of humans. THS-exposed mice show alterations in multiple organ systems and excrete levels of NNAL (a tobacco-specific carcinogen biomarker) similar to those found in children exposed to SHS (and consequently to THS). In liver, THS leads to increased lipid levels and non-alcoholic fatty liver disease, a precursor to cirrhosis and cancer and a potential contributor to cardiovascular disease. In lung, THS stimulates excess collagen production and high levels of inflammatory cytokines, suggesting propensity for fibrosis with implications for inflammation-induced diseases such as chronic obstructive pulmonary disease and asthma. In wounded skin, healing in THS-exposed mice has many characteristics of the poor healing of surgical incisions observed in human smokers. Lastly, behavioral tests show that THS-exposed mice become hyperactive. The latter data, combined with emerging associated behavioral problems in children exposed to SHS/THS, suggest that, with prolonged exposure, they may be at significant risk for developing more severe neurological disorders. These results provide a basis for studies on the toxic effects of THS in humans and inform potential regulatory policies to prevent involuntary exposure to THS.
PLoS ONE 01/2014; 9(1):e86391. DOI:10.1371/journal.pone.0086391 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Reactive oxygen species (ROS) and free radicals play important roles in the chemical transformation and adverse health effects of environmental aerosols. This work presents a simple and sensitive method for sampling and analysis of ROS using a packed column coated with a profluorescent nitroxide scavenger, proxyl fluorescamine (PF). Quantification was performed by extraction and analysis using HPLC with fluorescence detection. For comparison, the conventional method of collecting aerosols into dichlorofluorescin (DCFH) aqueous solution was used as a reference. The method was successfully applied to the determination of ROS in a model secondary organic aerosol (SOA) system generated by ozonolysis of nicotine, as well as in secondhand tobacco smoke (SHS). ROS concentrations between 50-565nmolm(-3) were detected in fresh SOA and SHS samples. After SHS aging for 22h, 13-18% of the initial ROS mass remained, suggesting the presence of persistent ROS. The new method offers better stability and reproducibility along with sensitivity comparable to that of DCFH (method detection limit of 3.2 and 1.4nmolm(-3) of equivalent H2O2 for PF and DCFH respectively). The PF probe was stable during storage at room temperature and not reactive with ozone or NOx, whereas DCFH in the particle-collecting liquid system was strongly influenced by ozone and NOx interferences. This case study provides a good basis for employing solid-phase supported PF for field measurement of specific ROS in other combustion systems (i.e. biomass burning, candles, and diesel exhaust) and environmental aerosols.
[Show abstract][Hide abstract] ABSTRACT: Formaldehyde emissions from fiberglass and polyester filters used in building heating, ventilation and air conditioning (HVAC) systems were measured in bench-scale tests using 10 and 17 cm2 coupons over 24 to 720 h periods. Experiments were performed at room temperature and four different relative humidity settings (20, 50, 65 and 80 % RH). Two different air flow velocities across the filters were explored: 0.013 and 0.5 m/s. Fiberglass filters emitted between 20 and 1000 times more formaldehyde than polyester filters under similar RH and airflow conditions. Emissions increased markedly with increasing humidity, up to 10 mg/h-m2 at 80% RH. Formaldehyde emissions from fiberglass filters coated with tackifiers (impaction oils) were lower than those from uncoated fiberglass media, suggesting that hydrolysis of other polymeric constituents of the filter matrix such as adhesives or binders was likely the main formaldehyde source. These laboratory results were further validated by performing a small field study in an unoccupied office. At 80% RH, indoor formaldehyde concentrations increased by 48-64 %, from 9-12 µg/m3 to 12-20 µg/m3, when synthetic filters were replaced with fiberglass filtration media in the HVAC units. Better understanding of reaction mechanisms and assessing their overall contributions to indoor formaldehyde levels will allow for an efficient control of this pollution source.
[Show abstract][Hide abstract] ABSTRACT: Exposure to thirdhand smoke (THS) is a newly described health risk. Evidence supports its widespread presence in indoor environments. However, its genotoxic potential, a critical aspect in risk assessment, is virtually untested. An important characteristic of THS is its ability to undergo chemical transformations during aging periods, as demonstrated in a recent study showing that sorbed nicotine reacts with the indoor pollutant nitrous acid (HONO) to form tobacco-specific nitrosamines (TSNAs) such as 4-(methylnitrosamino)-4-(3-pyridyl)butanal (NNA) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). The goal of this study was to assess the genotoxicity of THS in human cell lines using two in vitro assays. THS was generated in laboratory systems that simulated short (acute)- and long (chronic)-term exposures. Analysis by liquid chromatography-tandem mass spectrometry quantified TSNAs and common tobacco alkaloids in extracts of THS that had sorbed onto cellulose substrates. Exposure of human HepG2 cells to either acute or chronic THS for 24h resulted in significant increases in DNA strand breaks in the alkaline Comet assay. Cell cultures exposed to NNA alone showed significantly higher levels of DNA damage in the same assay. NNA is absent in freshly emitted secondhand smoke, but it is the main TSNA formed in THS when nicotine reacts with HONO long after smoking takes place. The long amplicon-quantitative PCR assay quantified significantly higher levels of oxidative DNA damage in hypoxanthine phosphoribosyltransferase 1 (HPRT) and polymerase β (POLB) genes of cultured human cells exposed to chronic THS for 24h compared with untreated cells, suggesting that THS exposure is related to increased oxidative stress and could be an important contributing factor in THS-mediated toxicity. The findings of this study demonstrate for the first time that exposure to THS is genotoxic in human cell lines.
[Show abstract][Hide abstract] ABSTRACT: The radiation field in a multi-plate photocatalytic reactor (MPPR) for air or water purification was modeled and optimized using a Monte Carlo stochastic method. The MPPR consists of parallel photocatalytic plates irradiated by cylindrical UV lamps orthogonal to the plates. The photocatalyst titanium dioxide (TiO2) is supported on the plates as a thin film. The photoreactor design is compact and offers a large irradiated photocatalytic surface area, a high degree of photon utilization, low pressure drop and a modular design which can facilitate scale-up. These features are desirable for the decontamination of indoor air in ventilation ducts or for water detoxification. The Monte Carlo method was applied to determine three dimensionless reactor performance parameters: the photon absorption efficiency (ϕ), the uniformity of the distribution of the dimensionless radiation intensity (η) and the overall photonic efficiency (Φ). The emission of photons from the light sources was simulated by the extensive source with superficial emission (ESSE) model. Simulations were performed by varying the catalyst reflectivity albedo, the number and the diameter of lamps, and the dimensions and spacing of the photocatalytic plates. Optimal design for a basic reactor module with one lamp was accomplished for lamp-diameter-to-plate-height ratio (β) of 0.7, while the plate-spacing-to-plate-height ratio (α) was correlated by [αoptimum = 0.191 β2 − 0.5597 β + 0.3854]. A multilamp arrangement leads to a feasible increase in the size and number of the plates and the irradiated photocatalytic surface area. The optimum design was validated by measuring the apparent quantum yield of the oxidation of toluene (7 ppmv) in a humidified air stream using immobilized TiO2 (Degussa P25). Experiments performed varying the geometrical parameter α correlated well with the model calculations, with maximum apparent quantum yield for α = 0.137. The results are directly transferable to the treatment of water by photocatalysis.
Chemical Engineering Journal 02/2013; 217:475–485. DOI:10.1016/j.cej.2012.11.085 · 4.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Self-cleaning surfaces containing TiO2 nanoparticles have been postulated to efficiently remove NOx from the atmosphere. However, UV irradiation of NOx adsorbed on TiO2 also was shown to form harmful gas-phase byproducts such as HONO and N2O that may limit their depolluting potential. Ambient pressure XPS was used to study surface and gas-phase species formed during adsorption of NO2 on TiO2 and subsequent UV irradiation at lambda = 365 nm. It is shown here that NO3-, adsorbed on TiO2 as a byproduct of NO2 disproportionation, was quantitatively converted to surface NO2 and other reduced nitrogenated species under UV irradiation in the absence of moisture. When water vapor was present, a faster NO3- conversion occurred, leading to a net loss of surface-bound nitrogenated species. Strongly adsorbed NO3- in the vicinity of coadsorbed K+ cations was stable under UV light, leading to an efficient capture of nitrogenated compounds.
[Show abstract][Hide abstract] ABSTRACT: Photocatalytic oxidation (PCO) air cleaning is a promising technology suitable for the elimination of a broad range of volatile organic compounds (VOCs). However, performance of poorly designed PCO systems may be affected by the formation of volatile aldehydes and other partially oxidized byproducts. This study explored the role of key design and dimensioning parameters that influence the effective removal of primary pollutants and can help reduce or eliminate the formation of secondary byproducts. A model pollutant mixture containing benzene, toluene, o-xylene, undecane, 1-butanol, formaldehyde and acetaldehyde was introduced at a constant rate in a 20-m3 environmental chamber operating at an air exchange rate of 1 h−1. Individual pollutant concentrations were kept at realistically low levels, between 2 and 40 μg m−3. A prototype air cleaner provided with flat or pleated PCO filtering media was operated in an external ductwork loop that recirculated chamber air at flow rates in the range 178–878 m3 h−1, corresponding to recycle ratios between 8.5 and 38. Air samples were collected upstream and downstream of the air cleaner and analyzed off-line to determine single-pass removal efficiency. The final-to-initial chamber concentration ratio was used to determine the global chamber removal efficiency for each pollutant. In the flat filter configuration, longer dwelling times of compounds on the TiO2 surface were attained by reducing the recirculation airflow by a factor of ∼5, leading to increasing total pollutant removal efficiency from 5% to 44%. Net acetaldehyde and formaldehyde removal was achieved, the later at airflow rates below 300 m3 h−1, illustrating the critical importance of controlling the contact time of primary and secondary pollutants with the TiO2 surface. The use of pleated media was shown to increase significantly the system performance by extending the dwelling time of pollutants on the irradiated surface of the PCO media, with a 70% degradation of target pollutants. With the pleated media, formaldehyde removal efficiency increased to 60%. Irradiation using either a UVC or a UVA lamp under identical flow conditions produced similar pollutant elimination. A simple correlation between the steady-state single pass removal efficiency and the global chamber removal efficiency was used to rationalize these experimental results and identify optimal operating conditions.
[Show abstract][Hide abstract] ABSTRACT: a b s t r a c t This study explores the potential environmental and energy benefits of using activated carbon fiber (ACF) filters for air cleaning in HVAC systems. The parallel aims for the air cleaning system were to enable reduced indoor exposures to volatile organic compounds (VOCs) and to simultaneously allow reduced rates and energy consumption for outdoor air ventilation. We evaluated the use of ACF media to adsorb VOCs from indoor air during repeated simulated 12-h to 24-h periods of occupancy. In a cyclic regen-eration process, VOCs were desorbed from the ACF media and vented outdoors to enable the next cycle of air cleaning. The VOC removal efficiency of the ACF media was measured using a 9.5-cm 2 ACF specimen exposed to a mixture of VOCs that included toluene, benzene, o-xylene, 1-butanol, limonene, undecane and formaldehyde at 29 C and 30% relative humidity. The concentrations of these model pollutants upstream of the ACF media were in the range 20e30 ppb, to simulate realistic conditions. Velocities through the ACF media were typical of those in normal particle filter systems (w0.5 m s À1). Initial tests were conducted to develop a modified multi-component Freundlich isotherm and estimate the maximum adsorption capacity of the media, which was determined to be 90 mg VOC per gram of ACF. Three different ACF regeneration methods were explored using relatively cleaner outdoor air under ambient conditions, with this air humidified, and with the filter heated. It was found that heating the ACF media to w150 C by circulation of a DC current through the fibers for a short period (15 min) yielded the best VOC removal results, allowing for subsequent consistent removal efficiencies of 70e80% for most VOCs. Regeneration with unheated outdoor air was also effective and used less energy (subsequent removal efficiency was 50e60% for most VOCs). ACF did not perform as well in eliminating formalde-hyde, for which a maximum removal of 25e30% was achieved with heated regeneration. A mass balance model indicated that the combination of ACF air cleaning and a 50% reduction in ventilation will decrease indoor concentrations of VOCs by 60%e80% and reduce formaldehyde concentrations by 12%e40%. Energy modeling indicated the potential to reduce the energy required for heating and cooling of ventilation air by 35% to almost 50%.
Building and Environment 01/2012; 47(1). DOI:10.1016/j.buildenv.2011.07.002 · 3.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated the adsorption capacity and photocatalytic removal efficiency of formaldehyde using a hectorite-TiO(2) composite in a bench flow reactor. The same experimental conditions were applied to pure TiO(2) (Degussa P25) as a reference. The catalysts were irradiated with either a UVA lamp (365 nm) or with one of two UVC lamps of 254 nm and 254+185 nm, respectively. Formaldehyde was introduced upstream at concentrations of 100-500 ppb, with relative humidity (RH) in the range 0-66% and residence times between 50 and 500 ms. Under dry air and without illumination, saturation of catalyst surfaces was achieved after ≈ 200 min for P25 and ≈ 1000 min for hectorite-TiO(2). The formaldehyde uptake capacity by hectorite-TiO(2) was 4.1 times higher than that of P25, almost twice the BET surface area ratio. In the presence of humidity, the difference in uptake efficiency between both materials disappeared, and saturation was achieved faster (after ≈ 200 min at 10% RH and ≈ 60 min at 65% RH). Under irradiation with each of the three UV sources, removal efficiencies were proportional to the Ti content and increased with contact time. The removal efficiency decreased at high RH. A more complete elimination of formaldehyde was observed with the 254+185 nm UV source.
[Show abstract][Hide abstract] ABSTRACT: The use of highly reflective “cool” roofing materials can decrease demand for air conditioning, mitigate the urban heat island effect, and potentially slow global warming. However, initially high roof solar reflectance can be degraded by natural soiling and weathering processes. We evaluated solar reflectance losses after three years of natural exposure reported in two separate databases: the Rated Products Directory of the US Cool Roof Rating Council (CRRC) and information reported by manufacturers to the US Environmental Protection Agency (EPA)'s ENERGY STAR® rating program. Many product ratings were culled because they were duplicative (within a database) or not measured. A second, site-resolved version of the CRRC dataset was created by transcribing from paper records the site-specific measurements of aged solar reflectance in Florida, Arizona and Ohio.Products with high initial solar reflectance tended to lose reflectance, while those with very low initial solar reflectance tended to become more reflective as they aged. Within the site-resolved CRRC database, absolute solar reflectance losses for samples of medium-to-high initial solar reflectance were 2–3 times greater in Florida (hot and humid) than in Arizona (hot and dry); losses in Ohio (temperate but polluted) were intermediate. Disaggregating results by product type—factory-applied coating, field-applied coating, metal, modified bitumen, shingle, single-ply membrane and tile—revealed that absolute solar reflectance losses were largest for field-applied coating, modified bitumen and single-ply membrane products, and smallest for factory-applied coating and metal products.The 2008 Title 24 provisional aged solar reflectance formula overpredicts the measured aged solar reflectance of 0–30% of each product type in the culled public CRRC database. The rate of overprediction was greatest for field-applied coating and single-ply membrane products and least for factory-applied coating, shingle, and metal products. New product-specific formulas of the form ρa′=0.20+β(ρi−0.20) can be used to estimate provisional aged solar reflectance ρa′ from initial solar reflectance ρi pending measurement of aged solar reflectance. The appropriate value of soiling resistance β varies by product type and is selected to attain some desired overprediction rate for the formula. The correlations for shingle products presented in this paper should not be used to predict aged solar reflectance or estimate provisional aged solar reflectance because the data set is too small and too limited in range of initial solar reflectance.Graphical abstractHighlights► Solar reflectance of a “cool” roof can be degraded by natural soiling and weathering. ► Absolute reflectance losses are 2–3 times greater in Florida (hot and humid) than in Arizona (hot and dry). ► Losses are largest for field-applied coating, modified bitumen and single-ply membrane products. ► Losses are smallest for factory-applied coating and metal products. ► New product-specific formulas estimate aged solar reflectance from initial solar reflectance.
Solar Energy Materials and Solar Cells 12/2011; 95(12):3385-3399. DOI:10.1016/j.solmat.2011.08.002 · 5.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Exposure to tobacco pollutants that linger indoors after smoking has taken place (thirdhand smoke, THS) can occur over extended periods and is modulated by chemical processes involving atmospheric reactive species. This study investigates the role of ozone and indoor surfaces in chemical transformations of tobacco smoke residues. Gas and particle constituents of secondhand smoke (SHS) as well as sorbed SHS on chamber internal walls and model materials (cotton, paper, and gypsum wallboard) were characterized during aging. After smoldering 10 cigarettes in a 24-m3 room size chamber, gas-phase nicotine was rapidly removed by sorption to chamber surfaces, and subsequently re-emitted during ventilation with clean air to a level of ∼10% that during the smoking phase. During chamber ventilation in the presence of ozone (180ppb), ozone decayed at a rate of 5.6h−1 and coincided with a factor of 5 less nicotine sorbed to wallboard. In the presence of ozone, no gas phase nicotine was detected as a result of re-emission, and higher concentrations of nicotine oxidation products were observed than when ventilation was performed with ozone-free air. Analysis of the model surfaces showed that heterogeneous nicotine-ozone reaction was faster on paper than cotton, and both were faster than on wallboard. However, wallboard played a dominant role in ozone-initiated reaction in the chamber due to its large total geometric surface area and sink potential compared to the other substrates. This study is the first to show in a room-sized environmental chamber that the heterogeneous ozone chemistry of sorbed nicotine generates THS constituents of concern, as observed previously in bench-top studies. In addition to the main oxidation products (cotinine, myosmine and N-methyl formamide), nicotine-1-oxide was detected for the first time.