Anthropogenic Volatile Organic Compounds Research Articles

Wavelength and NO<sub>x</sub> dependent complex refractive index of SOAs generated from the photooxidation of toluene

Abstract. Recently, secondary organic aerosols (SOAs) generated from anthropogenic volatile organic compounds have been proposed as a possible source of light-absorbing organic compounds, "brown carbon," in the urban atmosphere. However, the atmospheric importance of these SOAs remains unclear due to limited information about their optical properties. In this study, the complex refractive index (RI, m = n-ki values at 405, 532, and 781 nm of the SOAs generated during the photooxidation of toluene (toluene-SOAs) under a variety of initial nitrogen oxide (NOx = NO + NO2) conditions were examined by photoacoustic spectroscopy (PAS) and cavity ring-down spectroscopy (CRDS). The complex RI-values obtained in the present study and reported in the literature indicate that the k-value, which represents the light absorption of the toluene-SOAs, increased to shorter wavelengths at <532 nm, and the n-value also increased to shorter wavelengths from 781 to 355 nm. The k-values at 405 nm were found to increase from 0.0018 to 0.0072 with increasing initial NOx concentration from 109 to 571 ppbv. The nitrate to organics ratio of the SOAs determined using a high-resolution time-of-flight aerosol mass spectrometer (H-ToF-AMS) also increased with increasing initial NOx concentration. The RI-values of the SOAs generated during the photooxidation of 1,3,5-trimethylbenzene in the presence of NOx (1,3,5-TMB-SOAs) were also determined to investigate the influence of the chemical structure of the precursor on the optical properties of the SOAs, and it was found that the light absorption of the 1,3,5-TMB-SOAs is negligible at all of the wavelengths investigated (405, 532, and 781 nm). These results can be reasonably explained by the hypothesis that nitroaromatic compounds, such as nitrocresols, are the major contributors to the light absorption of the toluene-SOAs. Using the obtained RI-values, mass absorption cross sections of the toluene-SOAs at 405 nm were estimated to be 0.08–0.52 m2g−1 under typical conditions in an urban atmosphere during the daytime. These results indicate that light absorption by the SOAs potentially contributes to the radiation balance at ultraviolet wavelengths below ~400 nm, specifically when the mass concentrations of the anthropogenic SOAs are significant compared with other light-absorbing particles.

Understanding of the Fate of Atmospheric Pollutants Using a Process Analysis Tool in a 3-D Regional Air Quality Model at a Fine Grid Scale

The process analysis is performed for August and December, 2002 using the process analysis tool embedded in the Community Multiscale Air Quality (CMAQ) modeling system at a fine horizontal grid resolution of 4-km over an area in the southeastern U.S. that is centered at North Carolina. The objectives are to qunatify the contributions of major atmospheric processes to the formation of major air pollutants and provide the insights into photochemistry that governs the fate of these pollutants at a fine grid scale. The results show that emissions provide a dominant source for gases including ammonia (NH3), nitric oxide (NO), nitrogen dioxide (NO2), and sulfur dioxide (SO2) and Particulate Matter (PM) species including fine PM (PM2.5) and its composition such as sulfate, elemental carbon, primary organic aerosol, and other inorganic fine PM in both months. While transport acts as a major sink for NH3, NO, and SO2 at most sites and PM2.5 and most of PM2.5 composition at urban sites, it provides a major source for nitric acid (HNO3) and ozone (O3) at most sites in both months, and secondary PM species in August and most PM species in December at rural and remote sites. Gas-phase chemistry serves as a source for NO2 and HNO3 but a sink for O3 at urban and suburban sites and for NO and SO2 at all sites. PM processes contribute to the formation of PM2.5 and nitrate () at the urban and suburban sites and secondary organic aerosol (SOA) at most sites in December and ammonium () in both months. They reduce formation at most sites in August and at rural and remote sites in December and the formation of PM2.5 and SOA at most sites in August. Dry deposition is an important sink for all these species in both months. The total odd oxygen (Ox) production and the total hydroxyl radical (OH) reacted are much higher at urban and suburban sites than at rural sites. Significant amounts of OH are consumed by biogenic volatile organic compounds (BVOCs) in the rural and remote areas and a combination of anthropogenic VOCs (AVOCs) and BVOCs in urban and subareas areas in August and mainly by AVOCs in December. The amount of NO2 produced by the reactions of hydroperoxy radical (HO2) is similar to that of organic peroxy radical (RO2) at all sites in August but higher than that by the reactions of RO2 inDecember. The production rate of HNO3 due to the reaction of OH with NO2 dominates in both months. The ratio of the production rates of hydrogen peroxide (H2O2) and HNO3 (PH2O2/PHNO3) is a more robust photochemical indicator than the ratios of their mixing ratios (H2O2/HNO3) and the afternoon mixing ratios of NOy in both months, and it is highly sensitive to the horizontal grid resolution in August. The use of PH2O2/PHNO3 simulated at 4-km indicates a VOC-limited O3 chemistry in urban and suburban areas in August that was not captured in previous model simulations at a coarser grid resolution.

Volatile Organic Compounds in Roadside Environment of Hong Kong

Vehicular exhaust emissions are one of major sources of anthropogenic volatile organic compounds (VOCs) in urban areas of Pearl River Delta Region (PRDR). Six types of vehicle emission (VE)-dominated samples were collected at representative locations in Hong Kong in the winter of 2003. A total of 111 VOC species were quantified in the samples collected. n-Butane (31%) was the most abundant species in liquefied petroleum gas (LPG)-fueled VE-dominated samples, followed by propane (26%) and i-butane (25%). Toluene was the most abundant species in gasoline-fueled VE-dominated samples (16%), comprising about half of the quantified aromatic content. While ethene and ethyne have the greatest abundance in all diesel-fueled VE-dominated VOCs profiles (except at Tuen Mun Bus Depot). VOCs were also quantified at three roadside locations in Hong Kong. And ethene was the most abundant VOCs at roadside locations which accounted for 9.5 to 29% of the total quantified VOCs, except at Hong Kong Polytechnic University roadside monitoring station (PUX). Moreover, several VOCs were clearly in abundances in the roadside samples, namely toluene, ethyne, propane, ibutane, n-butane and i-pentane. Generally, strong and fair correlations were determined from the marker species of fuel vapor (i.e., LPG, gasoline, and diesel), which show significant fuel evaporation from vehicles in roadside environment of Hong Kong. Maximum incremental reactivity (MIR) was also calculated to evaluate the contributions of individual VOCs to ozone (O3) formation potential. The largest contributors to O3 production at Mong Kok roadside station (MKX) and Lok Ma Chau roadside station (LMX) were toluene (17 and 15% of the measured VOC reactivity, respectively), ethene (14 and 17% of the measured VOC reactivity, respectively), and propene (7 and 8% of the measured VOC reactivity, respectively), indicating the important roles of alkenes and aromatics in the ambient O3 formation.

Does urban vegetation mitigate air pollution in northern conditions?

It is generally accepted that urban vegetation improves air quality and thereby enhances the well-being of citizens. However, empirical evidence on the potential of urban trees to mitigate air pollution is meager, particularly in northern climates with a short growing season. We studied the ability of urban park/forest vegetation to remove air pollutants (NO2, anthropogenic VOCs and particle deposition) using passive samplers in two Finnish cities. Concentrations of each pollutant in August (summer; leaf-period) and March (winter, leaf-free period) were slightly but often insignificantly lower under tree canopies than in adjacent open areas, suggesting that the role of foliage in removing air pollutants is insignificant. Furthermore, vegetation-related environmental variables (canopy closure, number and size of trees, density of understorey vegetation) did not explain the variation in pollution concentrations. Our results suggest that the ability of urban vegetation to remove air pollutants is minor in northern climates.

Volatile organic compounds (VOCs) in urban air: How chemistry affects the interpretation of positive matrix factorization (PMF) analysis

Volatile organic compounds (VOCs) were measured online at an urban site in Beijing in August–September 2010. Diurnal variations of various VOC species indicate that VOCs concentrations were influenced by photochemical removal with OH radicals for reactive species and secondary formation for oxygenated VOCs (OVOCs). A photochemical age‐based parameterization method was applied to characterize VOCs chemistry. A large part of the variability in concentrations of both hydrocarbons and OVOCs was explained by this method. The determined emission ratios of hydrocarbons to acetylene agreed within a factor of two between 2005 and 2010 measurements. However, large differences were found for emission ratios of some alkanes and C8 aromatics between Beijing and northeastern United States secondary formation from anthropogenic VOCs generally contributed higher percentages to concentrations of reactive aldehydes than those of inert ketones and alcohols. Anthropogenic primary emissions accounted for the majority of ketones and alcohols concentrations. Positive matrix factorization (PMF) was also used to identify emission sources from this VOCs data set. The four resolved factors were three anthropogenic factors and a biogenic factor. However, the anthropogenic factors are attributed here to a common source at different stages of photochemical processing rather than three independent sources. Anthropogenic and biogenic sources of VOCs concentrations were not separated completely in PMF. This study indicates that photochemistry of VOCs in the atmosphere complicates the information about separated sources that can be extracted from PMF and the influence of photochemical processing must be carefully considered in the interpretation of source apportionment studies based upon PMF.

Observations of glyoxal and formaldehyde as metrics for the anthropogenic impact on rural photochemistry

Abstract. We present simultaneous fast, in-situ measurements of formaldehyde and glyoxal from two rural campaigns, BEARPEX 2009 and BEACHON-ROCS, both located in Pinus Ponderosa forests with emissions dominated by biogenic volatile organic compounds (VOCs). Despite considerable variability in the formaldehyde and glyoxal concentrations, the ratio of glyoxal to formaldehyde, RGF, displayed a very regular diurnal cycle over nearly 2 weeks of measurements. The only deviations in RGF were toward higher values and were the result of a biomass burning event during BEARPEX 2009 and very fresh anthropogenic influence during BEACHON-ROCS. Other rapid changes in glyoxal and formaldehyde concentrations have hardly any affect on RGF and could reflect transitions between low and high NO regimes. The trend of increased RGF from both anthropogenic reactive VOC mixtures and biomass burning compared to biogenic reactive VOC mixtures is robust due to the short timescales over which the observed changes in RGF occurred. Satellite retrievals, which suggest higher RGF for biogenic areas, are in contrast to our observed trends. It remains important to address this discrepancy, especially in view of the importance of satellite retrievals and in situ measurements for model comparison. In addition, we propose that RGF represents a useful metric for biogenic or anthropogenic reactive VOC mixtures and, in combination with absolute concentrations of glyoxal and formaldehyde, furthermore represents a useful metric for the extent of anthropogenic influence on overall reactive VOC processing via NOx. In particular, RGF yields information about not simply the VOCs dominating reactivity in an airmass, but the VOC processing itself that is directly coupled to ozone and secondary organic aerosol production.

Trends of chemical speciation profiles of anthropogenic volatile organic compounds emissions in China, 2005–2020

This study estimates the detailed chemical profiles of China’s anthropogenic volatile organic compounds (VOCs) emissions for the period of 2005–2020. The chemical profiles of VOCs for seven activity sectors are calculated, based on which the Photochemical Ozone Creation Potential (POCP) of VOCs for these sectors is evaluated. At the national level, the VOCs species emitted in 2005 include alkanes, alkenes and alkynes, aromatic compounds, alcohols, ketones, aldehydes, esters, ethers and halocarbons, accounting for 26.4 wt.%, 29.2 wt.%, 21.3 wt.%, 4.7 wt.%, 5.4 wt.%, 1.7 wt.%, 2.1 wt.%, 0.7 wt. % and 2.2 wt.% of total emissions, respectively. And during 2005-2020, their mass proportions would respectively grow or decrease by − 6.9%, − 32.7%, 7.3%, 65.3%, 34.7%, − 48.6%, 108.5%, 100.5%, and 55.4%. This change would bring about a 13% reduction of POCP for national VOCs emissions in the future. Thus, although the national VOCs emissions are expected to increase by 33% over the whole period, its ozone formation potential is estimated to rise only by 14%. Large discrepancies are found in VOCs speciation emissions among provinces. Compared to western provinces, the eastern provinces with a more developed economy would emit unsaturated hydrocarbons and benzene with lower mix ratios, and aromatic compounds except benzene, oxidized hydrocarbons and halocarbons with higher mix ratios. Such differences lead to lower POCP of VOCs emitted in eastern provinces, and higher POCP of VOCs emitted in western provinces. However, due to the large VOCs emissions from Chinese eastern region, the ozone formation potential of VOCs emission in eastern provinces would be much higher than those in western provinces by about 156%–235%.

On the gas‐particle partitioning of soluble organic aerosol in two urban atmospheres with contrasting emissions: 1. Bulk water‐soluble organic carbon

The partitioning of semi‐volatile compounds between the gas and particle phase influences the mass, size and chemical composition of the secondary organic aerosols (SOA) formed. Here we investigate the partitioning of water‐soluble organic carbon (WSOC) and the formation of SOA in Los Angeles (LA), California and Atlanta, Georgia; urban regions where anthropogenic volatile organic compound (VOC) emissions are dominated by vehicles, but are contrasted by an additional large source of biogenic VOCs exclusive to Atlanta. In Atlanta, evidence for WSOC partitioning to aerosol water is observed throughout the day, but is most prevalent in the morning. During drier periods (RH < 70%), the WSOC partitioning coefficient (Fp) was in proportion to the organic mass, suggesting that both particle water and organic aerosol (OA) can serve as an absorbing phase. In contrast, despite the higher average RH, in LA the aerosol water was not an important absorbing phase, instead, Fp was correlated with OA mass. Particle water concentrations from thermodynamic predictions based on measured inorganic aerosol components do not indicate significant differences in aerosol hygroscopicity. The observed different WSOC partitioning behaviors may be attributed to the contrasting VOC mixture between the two cities. In addition, different OA composition may also play a role, as Atlanta OA is expected to have a substantially more aged regional character. These results are consistent with our companion studies that find similar partitioning differences for formic acid and additional contrasts in SOA optical properties. The findings provide direct evidence for SOA formation through an equilibrium partitioning process.

Increase of ambient formaldehyde in Beijing and its implication for VOC reactivity

Abstract Influencing atmospheric OH radical budget and tropospheric ozone production, ambient formaldehyde (HCHO) is one of the key oxygenated volatile organic compounds (OVOCs). We present the variations on formaldehyde column densities in summertime in Beijing retrieved from ozone monitoring instrument (OMI) between 2005 and 2011. Satellite columns of HCHO correlated well with available ground-based measurements despite some noticeable differences. The orthogonal distance regression (ODR) method was used to estimate the ratio between satellite columns and ground-level concentrations, whereas ordinary least squares (OLS) method was used to fit the trend of ambient formaldehyde. The formaldehyde concentrations derived from HCHO columns were in the range of 7–12 ppbv and steadily increased at an approximate rate of 0.64 ppbv/yr (7.8% at 2005 level) with an uncertainty of 51%. VOC reactivity quantified by means of OH loss rates showed increasing contribution from formaldehyde and acetaldehyde, rising from 35% in 2005 to 40% in 2010, and decreasing contribution from anthropogenic VOCs, dropping from 49% in 2005 to 40% in 2010. More attention should be paid to understanding the net feedback of increasing formaldehyde to ozone formation potential.

Exploring the missing source of glyoxal (CHOCHO) over China

Recent comparisons between satellite observed and global model simulated glyoxal (CHOCHO) have consistently revealed a large unknown source of CHOCHO over China. We examine this missing CHOCHO source by analyzing SCIAMACHY observed CHOCHO vertical column densities (VCDs) using a Regional chEmical trAnsport Model (REAM). This missing source is first quantified by the difference between SCIAMACHY observed and REAM simulated CHOCHO VCDs (ΔCCHOCHO), which have little overlap with high biogenic isoprene emissions but are collocated with dense population and high anthropogenic NOxand VOC emissions. We then apply inverse modeling to constrain CHOCHO precursor emissions based on SCIAMACHY CHOCHO and find that this missing source is most likely caused by substantially underestimated aromatics emissions (by a factor of 4–10, varying spatially) in the VOC emission inventories over China used in current regional and global models. Comparison with in situ observations in Beijing, Shanghai, and a site in the Pearl River Delta shows that the large model biases in aromatics concentrations are greatly reduced after the inversion. The top‐down estimated aromatics emission is 13.4 Tg yr−1in total, about 6 times the bottom‐up estimate (2.4 Tg yr−1). The resulting impact on regional oxidant levels is large (e.g., ∼100% increase of PAN in the afternoon). Furthermore, since aromatics are important precursors of secondary organic aerosol (SOA), such an increase of aromatics could lead to ∼50% increase of global aromatic SOA production and thereby help to reduce the low bias of simulated organic aerosols over the region in previous modeling studies.

Comparison of the SAPRC07 and SAPRC99 photochemical mechanisms during a high ozone episode in Texas: Differences in concentrations, OH budget and relative response factors

The latest SAPRC photochemical mechanism SAPRC07 (S07), an update from SAPRC99 (S99), is implemented into the Community Multi-scale Air Quality (CMAQ) model and applied to simulate a high ozone episode during the Texas Air Quality Study 2000 (TexAQS 2000). The results from the S07 mechanism are compared with those from the S99 mechanism. In general, the predicted O3 concentrations by S07 are lower than those of S99 with maximum difference as high as 20%. The two mechanisms also show significant differences in the predicted OH, HNO3, PAN and HCHO concentrations. S99 predicts higher OH concentration by 7–20%, higher PAN by approximately 20–25% and higher HCHO by approximately 15% than S07. OH budget analysis suggests that OH propagation factor (POH) is higher in urban and industrial areas but lower in rural areas. Although S07 generally predicts similar or higher POH, S99 predicts higher new OH formation rate from H2O + O(1D) and leads to higher OH and thus higher O3 in most part of the domain. OH reactions with VOCs and CO accounts for a majority part of reacted OH. Secondary VOCs photolysis is not a main path of regenerated OH. New OH mainly comes from H2O + O(1D) reaction. Although the two mechanisms predict different ozone concentrations, the relative response factor (RRF) of ozone at rural, urban and industrial sites under emission controls of anthropogenic NOx and VOC controls by factors 0.6–1.4 predicted by the two mechanisms are very similar. This suggests that although the absolute predictions are different, both models will provide nearly identical attainment assessment in regulatory applications.

Determination and potential importance of diterpene (kaur-16-ene) emitted from dominant coniferous trees in Japan

Reactive volatile organic compounds (VOCs) are known to affect atmospheric chemistry. Biogenic VOCs (BVOCs) have a significant impact on regional air quality due to their large emission rates and high reactivities. Diterpenes (most particularly, kaur-16-ene) were detected in all of the 205 enclosure air samples collected over multiple seasons at two different sites from Cryptomeria japonica and Chamaecyparis obtusa trees, the dominant coniferous trees in Japan,. The emission rate of kaur-16-ene, was determined to be from 0.01 to 7.1μgdwg−1h−1 (average: 0.61μgdwg−1h−1) employing branch enclosure measurements using adsorbent sampling followed by solid phase–liquid extraction techniques. The emission rate was comparable to that of monoterpenes, which is known major BVOC emissions, collected from the same branches. In addition, total emission of kaur-16-ene at 30°C was estimated to exceed that of total anthropogenic VOC emissions.

Have primary emission reduction measures reduced ozone across Europe? An analysis of European rural background ozone trends 1996–2005

Abstract. National and European legislation over the past 20 yr, and the modernisation or removal of industrial sources, have significantly reduced European ozone precursor emissions. This study quantifies observed and modelled European ozone annual and seasonal linear trends from 158 harmonised rural background monitoring stations over a constant time period of a decade (1996–2005). Mean ozone concentrations are investigated, in addition to the ozone 5th percentiles as a measure of the baseline or background conditions, and the 95th percentiles that are representative of the peak concentration levels. This study aims to characterise and quantify surface European ozone concentrations and trends and assess the impact of the changing anthropogenic emission tracers on the observed and modelled trends. Significant (p<0.1) positive annual trends in ozone mean, 5th and 95th percentiles are observed at 54 %, 52 % and 45 % of sites respectively (85 sites, 82 sites and 71 sites). Spatially, sites in central and north-western Europe tend to display positive annual ozone trends in mean, 5th and 95th percentiles. Significant negative annual trends in ozone mean 5th and 95th percentiles are observed at 11 %, 12 % and 12 % of sites respectively (18 sites, 19 sites and 19 sites) which tend to be located in the eastern and south-western extremities of Europe. European-averaged annual trends have been calculated from the 158 sites in this study. Overall there is a net positive annual trend in observed ozone mean (0.16±0.02 ppbv yr−1 (2σ error)), 5th (0.13±0.02 ppbv yr−1) and 95th (0.16±0.03 ppbv yr−1) percentiles, representative of positive trends in mean, baseline and peak ozone. Assessing the sensitivity of the derived overall trends to the constituent years shows that the European heatwave year of 2003 has significant positive influence and 1998 the converse effect; demonstrating the masking effect of inter-annual variability on decadal based ozone trends. The European scale 3-D CTM CHIMERE was used to simulate hourly O3 concentrations for the period 1996–2005. Comparisons between the 158 observed ozone trends to those equivalent sites extracted from regional simulations by CHIMERE better match the observed increasing annual ozone (predominantly in central and north-western Europe) for 5th percentiles, than for mean or 95th ozone percentiles. The European-averaged annual ozone trend in CHIMERE 5th percentiles (0.13±0.01 ppbv yr−1) matches the corresponding observed trend extremely well, but displays a negative trend for the 95th percentile (−0.03±0.02 ppbv yr−1) where a positive ozone trend is observed. Inspection of the EU-averaged monthly means of ozone shows that the CHIMERE model is overestimating the summer month O3 levels. In comparison to trends in EMEP emissions inventories, with the exception of Austria-Hungary, we do not find that anthropogenic NOx and VOC reductions have a substantial effect on observed annual mean O3 trends in the rest of Europe. On a ten year time-scale presented in this study, O3 trends related to anthropogenic NOx and VOC reductions are being masked as a result of a number of factors including meteorological variability, changes in background ozone and shifts in source patterns.

亚热带城乡复合系统BVOC排放清单——以台州地区为例

VOCs(volatile organic compounds) are believed to have close relationships with the chemical composition and physical characteristics of the atmosphere.Biogenic VOCs(BVOCs) are more reactive than anthropogenic VOCs(AVOCs),can contribute to tropospheric ozone and secondary particle formation,and have indirect effects on climate change.Estimates of regional BVOC emissions are thus crucial input parameters of air quality models.However,most of the BVOC inventory work has concentrated on natural habitats in Europe,North America and some tropical regions.Although an increasing number of studies are being carried out in tropical and mid-latitude regions throughout Asia in recent years,few studies are concerned with humid subtropical areas,especially in urban areas.Here,a field survey of vegetation composition and distribution was conducted in a subtropical urban-rural complex,Greater Taizhou Area(28°01′—29°20′N,120°17′—121°56′E),Zhejiang Province.Different models were developed and used to estimate leaf biomass of the main tree species.BVOC were divided into isoprene,monoterpenes and other VOCs(OVOCs) and different algorithms were used calculate them separately.The isoprene emission rate data of the main tree species in this area was identified using a plant enclosure approach followed by a GC-PID analysis,while other emission data was compiled from measurements available in China.Tree distribution information,leaf biomass,plant emissions,and meteorological data were combined to investigate the BVOC emission intensity,temporal and spatial patterns and species features in Greater Taizhou Area.Results showed that the annual BVOC emissions of Taizhou in 2009 is 4.6×1010 g C.Isoprene,total monoterpenes and OVOCs emissions account for 93.8%,3.5% and 2.7%,respectively.In rural area,the emission intensity of bamboo forest(133.8 t C · km-2 · a-1) is two orders of magnitude higher than those of Pinus massoniana forest,Cunninghamia lanceolata forest and evergreen broad-leaved forests(0.9,0.8,0.6 t C · km-2 · a-1,respectively).So from the perspective of improving air quality,expansion of bamboo forests should be inhibited while increasing the proportion of evergreen broad-leaf forests.Within Taizhou city,the BVOC emission intensity of street and riparian trees is 2.4 t C · km-2 · a-1,while the emission intensity of trees in parks and residential areas is 1.6 t C · km-2 · a-1,both of which are higher than that of any rural forest types other than bamboo forest.Among the primary tree species within the built-up area,Salix babylonica,Albizia julibrissin,Sophora japonica and Liquidambar formosana exhibited high BVOC emission potential,while Cinnamomum camphora,Magnolia grandiflora and Ginkgo biloba have relatively low emission potential.There were no significant differences in the emission patterns between native and nonnative tree species in Taizhou area.Species with low BVOC emission potential should therefore be chosen for future in urban greening initiatives.The annual BVOC emissions of Taizhou are much higher than those of Beijing(1.6×1010 g C/a) and Hong Kong(1.6×1010 g C/a) because these areas vary in climate and vegetation characteristics.This study also provides a scientific basis for the selection of tree species and improvement of air quality in cities in similar climate zones as Taizhou.

Source Apportionment of Ambient Volatile Organic Compounds from Petroleum and Non-Petroleum Emissions

Volatile Organic Compounds (VOCs), precursors of photochemical smog and toxic substances, have attracted widespread attention of environmental communities for decades [1]. Petroleum products are often considered as the major sources of VOCs in the atmosphere. However, some VOCs may be emitted from non-petroleum products such as biogenic emissions and biomass burning. Hence, identification of emission sources and quantification of source contributions to ambient VOCs are prerequisite for the formulation and implementation of VOC related air pollution control measures and strategies. Source apportionment may also help to identify potential oilfield in a location through obtaining the concentrations of the tracers. Previous research suggests that high ozone (O 3 ) production rates in many locations are strongly associated with high anthropogenic VOC emissions [2-3]. Hence, effort has been made to identify and quantify source emissions of VOCs in different cities and regions so that photochemical air pollution could be controlled [4-5]. Receptor-oriented source apportionment models are the main tools for the source identification of pollutants and the estimation of source contributions to pollutant concentrations. The most widely used models are the Chemical Mass Balance (CMB) [4], Principal Component Analysis (PCA)/Absolute Principal Component Scores (APCS) [5], Positive Matrix Factorization (PMF) [6], and Graphical Ratio Analysis for Composition Estimates (GRACE)/Source Apportionment by Factors with Explicit Restriction (SAFER), incorporated in the UNMIX model [7]. Watson et al. [4] reviewed VOC source apportionment by CMB in more than 20 urban areas. Gasoline vehicle exhaust, liquid gasoline, and gasoline evaporation contributed over 50% of the ambient VOCs in many of these studies. Vega et al. [8] estimated VOC source apportionment in Mexico City in 1996–1997 and reported that vehicle exhaust made contribution of 54.9–63.8% and handling and distribution of Liquefied Petroleum Gas (LPG) 20.0–28.5%. Sosa et al. [9] re-conducted source apportionment in Mexico City using VOC data collected in 2000– 2001 and found that handling and distribution of LPG was the major source (42–52%), followed by vehicle exhaust (25–28%), asphalt works (12–14%) and cooking (5–10%). In Houston, refinery (26–35%), petrochemical and evaporative emissions (20–22%) and natural gas (13–17%) were the dominant sources of VOCs in 2003, while the major VOC sources in 2006 became natural gas/crude oil (32–39%), LPG (26%), fuel evaporation (20–23%) and vehicular exhausts (11–13%). All these studies have provided robust results for VOCs in the study areas.

SO<SUB align="right">2 effect on secondary organic aerosol from a mixture of anthropogenic VOCs: experimental and modelled results

The effect of SO 2 in the photooxidation of a mixture of anthropogenic precursors is studied. Four experiments are carried out in the EUPHORE outdoor chamber, adding different initial SO 2 concentrations in each experiment. The experimental secondary organic aerosol (SOA) obtained in the experiments is compared with the aerosol simulated by two air quality models (CMAQ and CHIMERE) under the same initial conditions. A simplified version of the models is designed in order to consider the closed system of the chamber, where only gas phase chemistry and aerosol formation take place. While the experimental results show a clear increase of the aerosol formed in the presence of increasing SO 2 concentrations, the models do not consider this enhancement in the simulations. The behaviour of the models points out the need of a way to implement this effect on anthropogenic secondary organic aerosol.

Sensitivity of ozone and aerosols to precursor emissions in Europe

We modelled the air quality in Europe during January and June 2006 using the MM5/CAMx model system and studied the sensitivity of ozone and aerosol formation to precursor emissions. Increased isoprene emissions by a factor of four in summer caused an increase in afternoon ozone by up to 10%. On the other hand, the effect on secondary organic aerosols (SOA) was very small. Reductions in NO x emissions are more effective to reduce ozone in a large part of Europe whereas anthropogenic VOC emission reductions are effective only around the urban areas. Particulate nitrate and organic aerosols are the main components of modelled PM2.5 concentrations in winter. In summer, organic aerosols dominate the aerosol composition. They are mainly secondary, produced from sesquiterpenes and monoterpenes as well as oligomerisation. Inorganic aerosol formation is more sensitive to ammonia emissions in winter. In summer, effects of NO x and NH 3 emission reductions are lower because of lower ammonium nitrate concentrations.

Emission ratios of anthropogenic VOC in northern mid-latitude megacities: observations vs. emission inventories in Los Angeles and Paris.

Emission ratios of anthropogenic VOC in northern mid-latitude megacities: observations vs. emission inventories in Los Angeles and Paris.

Budgets for nocturnal VOC oxidation by nitrate radicals aloft during the 2006 Texas Air Quality Study

[1] Industrial emissions in Houston, Texas, and along the U.S. Gulf Coast are a large source of highly reactive anthropogenic volatile organic compounds (VOCs), principally alkenes, that affect air quality in that region. Nighttime oxidation by either O3 or NO3 removes these VOCs. This paper presents a regional analysis of nighttime P-3 flights during the 2006 Texas Air Quality Study (TexAQS) to quantify the loss rates and budgets for both NO3 and highly reactive VOC. Mixing ratios and production rates of NO3 were large, up to 400 parts per trillion by volume (pptv) and 1–2 parts per billion by volume (ppbv) per hour, respectively. Budgets for NO3 show that it was lost primarily to reaction with VOCs, with the sum of anthropogenic VOCs (30–54%) and isoprene (10–50%) being the largest contributors. Indirect loss of NO3 to N2O5 hydrolysis was of lesser importance (14–28%) but was the least certain due to uncertainty in the aerosol uptake coefficient for N2O5. Reaction of NO3 with peroxy radicals was a small but nonzero contribution to NO3 loss but was also uncertain because there were no direct measurements of peroxy radicals. Net VOC oxidation rates were rapid (up to 2 ppbv VOC h−1 in industrial plumes) and were dominated by NO3, which was 3–5 times more important as an oxidant than O3. Plumes of high NO3 reactivity (i.e., short steady state lifetimes, on the order of 1 min) identified the presence of concentrated emissions of highly reactive VOCs from the Houston Ship Channel (HSC), which, depending on the particular VOC, may be efficiently oxidized during overnight transport.

Mass absorption efficiency of elemental carbon and water-soluble organic carbon in Beijing, China

Abstract. The mass absorption efficiency (MAE) of elemental carbon (EC) in Beijing was quantified using a thermal-optical carbon analyzer. The MAE measured at 632 nm was 8.45±1.71 and 9.41±1.92 m2 g−1 during winter and summer respectively. The daily variation of MAE was found to coincide with the abundance of organic carbon (OC), especially the OC to EC ratio, perhaps due to the enhancement by coating with organic aerosol (especially secondary organic aerosol, SOA) or the artifacts resulting from the redistribution of liquid-like organic particles during the filter-based absorption measurements. Using a converting approach that accounts for the discrepancy caused by measurements methods of both light absorption and EC concentration, previously published MAE values were converted to the equivalent-MAE, which is the estimated value if using the same measurement methods as used in this study. The equivalent-MAE was found to be much lower in the regions heavily impacted by biomass burning (e.g., below 2.7 m2 g−1 for two Indian cities). Results from source samples (including diesel exhaust samples and biomass smoke samples) also demonstrated that emissions from biomass burning would decrease the MAE of EC. Moreover, optical properties of water-soluble organic carbon (WSOC) in Beijing were presented. Light absorption by WSOC exhibited strong wavelength (λ) dependence such that absorption varied approximately as λ−7, which was characteristic of the brown carbon spectra. The MAE of WSOC (measured at 365 nm) was 1.79±0.24 and 0.71±0.20 m2 g−1 during winter and summer respectively. The large discrepancy between the MAE of WSOC during winter and summer was attributed to the difference in the precursors of SOA such that anthropogenic volatile organic compounds (AVOCs) should be more important as the precursors of SOA in winter. The MAE of WSOC in Beijing was much higher than results from the southeastern United States which were obtained using the same method as used in this study, perhaps due to the stronger emissions of biomass burning in China.