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Atmospheric Environment (v.40, #10)
Impact of urban heat island on regional atmospheric pollution by C. Sarrat; A. Lemonsu; V. Masson; D. Guedalia (pp. 1743-1758).
The purpose of this work is to study the impact of an urban land cover on local meteorology and spatial distribution of atmospheric pollutants over the Paris region. One anticyclonic episode from the ESQUIF campaign was simulated using the meso-scale meteorological and chemical Meso-NHC model coupled to the town energy balance (TEB) urban canopy model. A control simulation was also performed without implementing TEB in order to quantify the effect of the urban parameterization. Both meteorological and chemical model outputs were evaluated against the data collected during the experiment and most of the results are improved when TEB is applied. The simulation indicates the formation of an urban heat island (UHI) over Paris which is stronger at night than during day. The structure of the atmospheric boundary layer is also strongly influenced by the city. The present study shows that both nocturnal and diurnal urban effects have an important impact on the primary and secondary regional pollutants, more specifically the ozone and the nitrogen oxide (NO x). The spatial distribution and the availability of pollutants are significantly modified by the urbanized area mainly due to enhanced turbulence.
Keywords: Regional atmospheric pollution; Urban area micrometeorology; Urban heat island; Urban boundary layer
Volatile organic compounds from vegetation in southern Yunnan Province, China: Emission rates and some potential regional implications by Chris Geron; Sue Owen; Alex Guenther; Jim Greenberg; Rei Rasmussen; Jian Hui Bai; Q.J. Qing-Jun Li; Brad Baker (pp. 1759-1773).
Little information is currently available regarding emissions of biogenic volatile organic compounds (BVOCs) in southern Asia. To address the need for BVOC emission estimates in regional atmospheric chemistry simulations, 95 common plant species were screened for emissions of BVOC in and near the Xishuangbanna Tropical Biological Gardens in southern Yunnan Province, Peoples’ Republic of China in February 2003. In situ measurements with leaf cuvettes and branch bag enclosures were used in combination with portable gas chromatography, flame ionization, photoionization, and mass spectral detection to identify and quantify BVOC emissions. Forty-four of the species examined emitted isoprene at rates exceeding 20μg Cg−1 (leaf dry weight) h−1. An emphasis was placed on the genus Ficus, which is important in the region and occupies a wide range of ecological niches. Several species in the footprint of a nearby flux tower were also examined. Several palm species and an abundant fern ( Cyclosorus parasiticus) emitted substantial amounts of isoprene, and probably accounted for observed daytime mean isoprene fluxes from the understory of a Hevea brasiliensis plantation of 1.0 and 0.15mgCm−2h−1 during the wet and dry seasons, respectively. These measurements verify that both the forest floor and canopy in this region can be sources of isoprene. Monoterpene emissions exceeded 1.0μg-Cg−1 (leaf dry weight) h−1 from only 4 of 38 species surveyed, including some Ficus species and H. brasiliensis. However most of the trees of the latter species were sparsely foliated due to dry season senescence, and emission factors are approximately an order of magnitude lower than those reported during the wet season. BVOC emission rates and physiology of many species are impacted by reduced moisture availability, especially Mangifera indica. South Asia is a region undergoing rapid landuse change and forest plantation establishment, with large increases in area of high BVOC-emitting species in the genera Bambusa, Elaeis, Eucalyptus, Hevea, Pinus, and Populus (among others). This could result in profound changes in atmospheric chemistry in these regions, for instance, terpene emissions from H. brasiliensis could increase wet season biogenic organic aerosol burdens by approximately a factor of 2 in the Xishuangbanna region. Increases in plantation area established with high isoprene emitting species, (e.g. Bambusa spp. and Eucalyptus spp.) are also projected for China and other parts of Southeast Asia in the near future. Thus, landcover change in South Asian landscapes is usually associated with large increases in BVOC flux with the potential to alter the atmospheric chemical composition and air quality over this rapidly developing region.
Keywords: Isoprene; Monoterpene; Biogenic volatile organic compounds; Leaf temperature; Photosynthetically active radiation; Emission factor; Hevea brasiliensis; Arecaceae; Fern; Ficus; Xishuangbanna tropical biological garden
Air quality forecasting using a hybrid autoregressive and nonlinear model by Asha B. Chelani; S. Devotta (pp. 1774-1780).
The usual practices of air quality time-series forecasting are based on applying the models that deal with either the linear or nonlinear patterns. As the linear or nonlinear behavior of the time series is not known in advance, one applies the number of models and finally selects the one, which provides the most accurate results. The air pollutant concentration time series contain patterns that are not purely linear or nonlinear and applying either technique may give inadequate results. This study aims to develop a hybrid methodology that can deal with both the linear and nonlinear structure of the time series. The hybrid model is developed using the combination of autoregressive integrated moving average model, which deals with linear patterns and nonlinear dynamical model. To demonstrate the utility of the proposed technique, nitrogen dioxide concentration observed at a site in Delhi during 1999 to 2003 was utilized. The individual linear and nonlinear models were also applied in order to examine the performance of the hybrid model. The performance is compared for one-step and multi-step ahead forecasts using the error statistics such as mean absolute percentage error and relative error. It is observed that hybrid model outperforms the individual linear and nonlinear models. The exploitation of unique features of linear and nonlinear models makes it a powerful technique to predict the air pollutant concentrations.
Keywords: Time-series forecasting; ARIMA; Nonlinear dynamics; Hybrid model
Development of diffuse reflectance infrared Fourier transform spectroscopy for the rapid characterization of aerosols by Ying I. Tsai; S.-C. Su-Ching Kuo (pp. 1781-1793).
In this study, the viability of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) for quantitative analysis of atmospheric aerosols is assessed. DRIFTS-derived absorption frequencies of the functional groups contained in aerosols are calibrated using ion chromatography (IC) and the calibrated concentrations are applied in an analysis of the major salt species contained in aerosols of various diameters collected in the city of Tainan in southern Taiwan. We found that the average discrepancy between measurements of SO42−, NH4+ and NO3− content from IC and DRIFTS was always <2% (1.21% for SO42−, 0.41% for NH4+, and 0.61% for NO3−), indicating that these two methods yield similar results and thus demonstrating that DRIFTS is a practical method for measuring these inorganic salts in aerosols. Results of the DRIFTS measurements indicate that the wavenumber absorbed by SO42− changes with increasing or decreasing SO32−, demonstrating that SO42− is formed from SO32− via SO2. Additionally, (NH4)2SO4 and NH4NO3, distributed in 0.10–0.32μm (condensation mode) and 0.56–1.8μm (droplet mode) particles, are shown to be the combination forms of secondary aerosols in the study area.
Keywords: Drifts; PM; 2.5; aerosols; Size distribution
Cloud droplet activation of saccharides and levoglucosan particles by Rosenorn Thomas Rosenørn; Gyula Kiss; Merete Bilde (pp. 1794-1802).
This study is focused on the ability of water-soluble organic compounds from wood combustion to act as cloud condensation nuclei. In particular, we have studied glucose, fructose, and mannose (monosaccharides), lactose, maltose, and sucrose (disaccharides) and levoglucosan. Critical supersaturations for dry particle sizes in the range 40–150nm were measured using a static thermal diffusion cloud condensation nucleus counter. For glucose and sucrose, critical supersaturations were calculated by applying Köhler theory in three different ways: using water activities from literature, using water activity calculated assuming a van’t Hoff factor of 1, and using osmolality-derived water activity values. Critical supersaturations for the other compounds were calculated using water activity calculated assuming a van’t Hoff factor of 1 and with osmolality-derived water activities (except for mannose and Levoglucosan). Calculated critical supersaturations agreed well with experimental data in all cases. For particles of the same size, the disaccharides (lactose, maltose and sucrose) were found to activate at a significantly higher critical supersaturations than the monosaccharides and levoglucosan. This is consistent with Köhler theory and is due to the higher molar mass of the disaccharides.
Keywords: Glucose; Fructose; Mannose; Lactose; Maltose; Sucrose; Levoglucosan; Water-soluble organic compounds; CCN; Aerosol
Identification and spatiotemporal variations of dominant PM10 sources over Hong Kong by Zibing Yuan; Alexis Kai Hon Lau; Hongyi Zhang; Jian Zhen Yu; Peter K.K. Louie; Jimmy C.H. Fung (pp. 1803-1815).
We report here an application of two advanced receptor models, Unmix and positive matrix factorization (PMF), for source identification of PM10 in Hong Kong (HK) using chemical composition measurements from a monitoring network between July 1998 and December 2002. Seven and nine sources were identified by Unmix and PMF, respectively, from a combined dataset including all monitoring stations. Source categories were determined based on both component abundances in the source profiles and their temporal and spatial characteristics. Overall, secondary sulfate and local vehicle emissions gave the largest contribution to PM10 in HK (25% each), followed by secondary nitrate (12%). Contributions from other source types were below 10%. Analyses were also carried out to help infer the seasonal variations in the contributions of local and regional sources to the PM10 mass. We found that regional sources accounted for about 60% of the ambient PM10 mass on an annual basis, and even higher (70%) during winter, suggesting that regional air quality management strategies are important. On the other hand, many species with significant adverse health impact were produced locally, suggesting that local control measures should be continued or even strengthened for better protection of public health in HK.
Keywords: Source apportionment; PM; 10; Positive matrix factorization; Unmix; Hong Kong
Formulating the relationship between ozone pollution features and the transition value of photochemical indicators by T.-F. Tu-Fu Chen; K.-H. Ken-Hui Chang (pp. 1816-1827).
Indicator transition value represents the value when O3 sensitivity transfers from VOC-sensitive to NO x-sensitive conditions. The applicability of the indicator transition value for O3 sensitivity is inconsistent in the past model studies. Thus, this study is undertaken to analyze the variation of the indicator transition value under different conditions. Initially, a three-dimensional (3D) Eulerian air quality model is adopted to predict spatial and temporary O3 concentrations during a particular 4-day episode in Taiwan. The methodology for determining indicator transition values, which is different from those used in other studies, is as follows. First, the peak O3 isopleth profile for each target grid cell in the modeling domain is established to determine the transition line based on 25 combinations of NO x and VOC emission reduction. The results are then compared with the isopleth profiles of concurrent indicator to determine the transition value of eight indicators for each target grid cell. The daily spatial distribution of indicator transition values for all grid cells in the modeling domain is different during the 4-day simulation period. Secondly, the ratio of NO z/NO y, NO y and O3 are used to describe the pollution features of air mass, and then a set of equations is developed to illustrate their relationship with the indicator transition value. Finally, the capability of these equations to assess O3 sensitivity is evaluated. The H2O2/HNO3 ratio is found to be the best indicator among the eight indicators evaluated. The indicator transition value equation for air mass (ITVEAM) for H2O2/HNO3 is then constructed and the results described well the spatial variation during the 4-day simulation period. The ITVEAM along with the observed H2O2/HNO3 can be used to determine which precursor controls O3 production, especially during the O3 episode period. As a result, it can guide an emission reduction strategy to improve O3 concentration.
Keywords: Ozone sensitivity; Ozone precursor; Three-dimensional grid model
Concentrations and emissions of gasoline and other vapors from residential vehicle garages by Stuart Batterman; Gina Hatzivasilis; Chunrong Jia (pp. 1828-1844).
High concentrations of airborne volatile organic compounds (VOCs) may be present in residential garages due to emissions from vehicles, lawnmowers, storage containers, and many other items stored in the garage. VOC emissions will ultimately be transported into ambient air and, if the garage is attached to a residence or other building, into living spaces. This study reports on VOC concentrations and emissions at 15 residential garages in Michigan that varied in type, size, use and other characteristics. VOCs were measured in garages and in outside air using 4-day passive sampling, thermal desorption, and GC-MS analysis. Effective air exchange rates (AERs) were determined using a perfluorocarbon tracer gas and the constant injection method. A modeling analysis shows the effect of time-varying ventilation. To estimate temporal and spatial variability, concentrations were measured on 7 subsequent occasions at multiple locations in one garage. This garage was well-mixed, and the temporal variation in AERs and concentrations was modest. Across the 15 garages, 36 different VOCs in garage air, and 20 in ambient air, were quantified. Source groups identified and attributed to garage emissions included evaporated gasoline, solvents, paints, oils, and cleaners. Concentrations of gasoline-related VOCs in most garages were high, e.g., benzene levels reached 159μgm−3 in one garage. TVOC emissions per garage averaged 3.0±4.1gday−1, and AERs averaged 0.77±0.51h−1. VOC concentrations and AERs were not strongly correlated to observed house, garage or meteorological factors, but appeared largely dependent on occupant activities (opening of the garage door) and VOC sources present. This study quantifies the importance of attached garages as VOC sources, and the results are significant for understanding and mitigating indoor exposures, and for estimating emissions for source inventory purposes.
Keywords: Air exchange; Indoor air; Garages; Gasoline; Volatile organic compounds
The effect of chemical composition and size distribution of aerosol particles on droplet formation and albedo of stratocumulus clouds by I. Geresdi; Meszaros E. Mészáros; Molnar A. Molnár (pp. 1845-1855).
A numerical model was applied to simulate the evolution of water droplets on aerosol particles with different sizes and chemical compositions. The detailed microphysical model was incorporated into a one-dimensional parcel model to investigate the indirect effects of aerosol particles on climate. The calculations were initiated with different aerosol size distributions observed during the field measurements in 1973–1976 and at the end of the 20th century in rural Hungary. The effect of changes in the characteristics of aerosol particles during this time period on the number concentration of water droplets formed was calculated at different cloud base updraft velocities. It was found that about 10% of sulfate particles and about 1% of organic aerosol particles with radius larger than 0.025μm take part in drop formation if the updraft velocity is weak (0.1ms−1). Mostly haze particles form on this type of aerosol particles in this case: the majority of cloud droplets come into being on sulfate particles. If the updraft velocity is 1ms−1 at the cloud base, a larger fraction (≈30%) of the organic aerosol particles become activated. On the basis of our calculations, it is concluded that the observed modification of aerosol content resulted in a decrease in albedo of stratocumulus clouds of about 0.02 in the Central European region. If only the sulfate particles are considered, the corresponding albedo decrease is higher, about 0.03. The presence of soot in the aerosol particles, to some extent, mitigates the decrease of the albedo caused by the decrease of sulfate content.
Keywords: Aerosol; Sulfate and organic particles; Indirect climate effects
Analysis of the seasonal variation of ozone in the boundary layer in East Asia using the Community Multi-scale Air Quality model: What controls surface ozone levels over Japan? by Kazuyo Yamaji; Toshimasa Ohara; Itsushi Uno; Hiroshi Tanimoto; J.-i. Jun-ichi Kurokawa; Hajime Akimoto (pp. 1856-1868).
Ozone (O3) concentrations in East Asia were simulated using the Community Multi-scale Air Quality model and their reproducibility was confirmed by comparing with observation data at Japanese monitoring sites. The model can reproduce the seasonal variation of surface O3 over Japan. In particular, for the southern parts of Japan, simulated surface O3 concentrations are strongly correlated with observations. Surface O3 distribution over East Asia varies dynamically from season to season according to the meteorological condition. In May and June, 2-month average O3 concentrations in the boundary layer are highest, 55–70ppbv over East China and Japan at 35–40°N. We estimated the seasonal variation of the contribution of chemically produced O3 by east Asian regional emissions. In the summertime, the contribution of the regional Asian emissions to O3 concentrations is around 40–70% over most of China, and the highest is 60–70% (<35ppbv) at the mouth area of Yantze River. This suggests that O3 concentrations over East Asia are strongly influenced by the chemical production by regional emissions during summer season. However, the inflow from outside of this model domain also contributes substantial O3 concentration over East Asia and its contribution is predominant in winter and early spring. The seasonal change of O3 concentrations over Japan is characterized by two peaks in spring and autumn and summer minimum. The spring peak event in 2002 consists of split peaks: the first peak in Mar–Apr is mainly influenced by the inflow from outside of this model domain, the second spring peak between May and June is mainly influenced by chemically produced O3 by regional emissions. During the summer season, O3 concentrations are the lowest over year because of the weak Asian outflow and northward penetration of the marine air mass.
Keywords: Ozone; Seasonal variation; East Asia; Regional emissions; Chemical transport model
A critical review and analysis of the use of exposure- and flux-based ozone indices for predicting vegetation effects by Robert C. Musselman; Allen S. Lefohn; William J. Massman; Robert L. Heath (pp. 1869-1888).
Early studies of plant response to ozone (O3) utilized concentration-based metrics, primarily by summarizing the commonly monitored hourly average data sets. Research with the O3 concentration parameter led to the recognition that both peak concentrations and cumulative effects are important when relating plant response to O3. The US and Canada currently use O3 concentration-based (exposure-based) parameters for ambient air quality standards for protecting vegetation; the European countries use exposure-based critical levels to relate O3 to vegetation response. Because plant response is thought to be more closely related to O3 absorbed into leaf tissue, recent research has been focused on flux-based O3 parameters. Even though flux-based indices may appear to be more biologically relevant than concentration-based indices, there are limitations associated with their use. The current set of flux-based indices assumes that the plant has no defense mechanism to detoxify O3. This is a serious limitation. In this paper, we review the literature on exposure- and flux-based indices for predicting plant response. Both exposure- and flux-based metrics may overestimate plant response. At this time, flux-based models that take into consideration detoxification mechanisms (referred to as effective flux) provide the best approach to relate O3 to plant response. However, because there is considerable uncertainty in quantifying the various defense mechanisms, effective flux at this time is difficult to quantify. Without adequate effective-flux based models, exposure-based O3 metrics appear to be the only practical measure for use in relating ambient air quality standards to vegetation response.
Keywords: Dose; Effective flux; Nocturnal; Threshold; Uptake
Formation of secondary organic aerosol from the reaction of styrene with ozone in the presence and absence of ammonia and water by Kwangsam Na; Chen Song; David R. Cocker III (pp. 1889-1900).
We report on a comprehensive investigation of the influence of ammonia and water on secondary organic aerosol (SOA) formation from the styrene–ozone system. The presence of ammonia and water each affected the gas-phase chemistry leading to SOA formation, thereby impacting the total aerosol yield for the system. Two lumped products using the classic semi-empirical gas–particle equilibrium model ( α1, K1, α2, and K2 were estimated as 0.0490, 0.3410, 0.1439, and 0.0040, respectively) were sufficient to predict SOA formation in the dry styrene–ozone system. We propose 3,5-diphenyl-1,2,4-trioxolane and a hydroxyl-substituted ester as the major aerosol-forming products in the dry, ammonia-free styrene ozonolysis system. Addition of excess ammonia after SOA formation rapidly and significantly reduced the aerosol volume suspended in the chamber. We believe this is due to rapid decomposition of the 3,5-diphenyl-1,2,4-trioxolane and the hydroxyl-substituted ester by nucleophilic attack from the ammonia molecule. Additional experiments with α-methylstyrene/ozone produced SOA that was unaffected by ammonia, suggesting that the addition of a methyl group led to SOA that stearically hindered nucleophilic attack by the ammonia molecule. The presence of water vapor prior to styrene oxidation was found to reduce SOA formation, likely due to inhibition of the formation of 3,5-diphenyl-1,2,4-trioxolane.
Keywords: SOA; Styrene; Ozonolysis; Ammonia; Water vapor
Evaluation of arsenical emission from semiconductor and opto-electronics facilities in Hsinchu, Taiwan by H.M. HungMin Chein; Y.-D. Yu-Du Hsu; Shankar G. Aggarwal; T.-M. Tzu-Ming Chen; C.-C. Chun-Chao Huang (pp. 1901-1907).
Semiconductor and opto-electronics industries use many chemicals including arsenics in manufacturing processes. Thus, the process vent stream contains toxic air pollutants including arsine and other arsenic compounds, and poses a potential source for the atmospheric arsenic. Limited data are published on arsenic risk assessment and work place condition for electronics industries. Moreover, as per our best knowledge there is no report available on arsenic pollution from the exhaust of semiconductor and opto-electronic industries. In this study, the total arsenic (arsenic compounds as arsenic in gaseous and particulate phase) concentration was measured in the flue gas of 20 stacks of different semiconductor and opto-electronics facilities situated in Science Based Industrial Park (SBIP), Hsinchu, Taiwan during August–September 2002. Ambient concentration of particulate arsenic (arsenic compounds as arsenic) was measured at 15 sites of SBIP twice, i.e. in September and October 2002. The concentration of the total arsenic in the flue gas was from 0 to 55.92μgm−3 with the emission rate from 0 to 0.1427gh−1 for the facilities. The ambient arsenic concentration was from 0 to 120ngm−3. The ambient air level goal (AALG) of arsenic compound is 4.6×10−5μgm−3, if the lifetime cancer probability (LCP) level is 1.0×10−6. Based on simple risk assessment model, we used Industrial Source Complex Short Term 3 (ISCST3) model to calculate the maximum ground level concentration and employed the value of AALG; the emission limit of arsenic compounds from a factory was determined to be less than 1.0×10−5kgh−1. On comparison, it was concluded that the arsenical emission of 11 out of 20 facilities was higher than the limited value.
Keywords: Semiconductor and opto-electronics facilities; Arsenical emission; Ambient concentration; Risk assessment