Ambient Concentrations Of Volatile Organic Compounds Research Articles

Characterization and source apportionment of ambient VOC concentrations: Assessing ozone formation potential in the Barnett shale oil and gas region

Atmospheric concentration and distribution of volatile organic compounds (VOC) are influenced by localized emissions and the fate and transport of secondary products formed through photochemical reactions. This study identifies the sources of VOC and its contribution to ozone formation in the Barnett Shale region, specifically in Denton, Texas, during the ozone seasons of 2015 through 2022. A total of 31 critical ozone precursor VOC compounds were observed at this site with an average total VOC concentration of 146 ppb-C, with n-alkanes from extensive oil and gas activities in the area contributing to 96.64% of the total VOC. Source apportionment using dispersion normalized positive matrix factorization (DN-PMF) identified eight VOC sources, with natural gas emissions (72%) being the dominant source followed by a combined source of natural gas combustion and aviation emissions (8.3%). Ozone formation potential (OFP) by VOC species was calculated using the propylene-equivalent concentration (propy-equiv) method. OFP calculated for all the apportioned sources highlighted that natural gas sources contributed significantly to the ozone formation in this region besides isoprene from biogenic sources and reactive alkenes from urban and industrial activities. This study underscores the critical role of slow-reacting n-alkanes along with other highly reactive VOC from urban and industrial sources influencing ambient air quality and it identifies strategies for mitigating ground-level ozone in urban areas affected by oil and gas extraction and production.

Assessing VOC emissions from different gas stations: impacts, variations, and modeling fluctuations of air pollutants

Gas stations distributed around densely populated areas are responsible for toxic pollutant emissions such as volatile organic compounds (VOCs). This study aims to measure VOCs emission from three different kinds of gas stations to determine the extent of pollution from the gas stations and the most frequent type of VOC compound emitted. The concentrations of ambient VOCs at three refueling stations with a different type of fuels in Mashhad were monitored. The result of this study showed that CNG fuel stations are less polluting than petrol stations. In all the studied sites, the highest concentrations were related to xylene isomers, irrespective of the fuel type. Total VOCs at the supply of both compressed natural gas (CNG) and gasoline stations was 482.36 ± 563.45 µg m−3. At a CNG station and a gasoline station, total VOC concentrations were 1363.4 ± 1975 µg m−3 and 410.29 ± 483.37 µg m−3, respectively. The differences in concentrations of toluene and m,p-xylene between the fuel stations can be related to the quality and type of fuel, vapor recovery technology, fuel reserves, dripless nozzles, traffic density in these stations, meteorological conditions and the location of sampling sites. The combination of a sine function and a quadratic function could model the fluctuation behavior of air pollutants like m,p-xylene. In all the sites, the highest concentrations were related to xylene isomers, irrespective of the type of fuel. The changing rate of m,p-xylene pollutant in each station was also modeled in this study.

Source apportionment of measured volatile organic compounds in Maricopa County, Arizona

ABSTRACT With the goal of corroborating existing emissions inventories of volatile organic compounds (VOCs), a statistical analysis was undertaken on measured ambient VOC concentrations in Maricopa County, Arizona. The Chemical Mass Balance (CMB) model was used to generate emissions source contribution estimates based on ambient VOC concentrations collected at the JLG Supersite in Phoenix, Arizona, and emissions source profiles obtained from EPA’s SPECIATE database. With trial-and-error, optimal model performance using a combination of emissions source profiles yielded source contribution estimates which could be compared to existing regulatory engineering-based emissions inventories. The ultimate objective of this study is to offer a comparison to the “top-down” emissions modeling via CMB and the “bottom-up” modeling traditionally used in preparing emission inventories to identify possible discrepancies and help direct future investigations to better understand local air quality. The methods used to develop the “bottom-up” inventory rely upon sound modeling developed to accurately capture emissions from various source categories. The results show discrepancies between the “bottom-up” and “top-down” emission inventory for VOC emissions from biogenic and natural gas combustion sources, suggesting that the emission strength from these source categories should be further investigated. Implications: The following implication statement has been prepared for the manuscript titled Source Apportionment of Measured Volatile Organic Compounds in Maricopa County, Arizona. The purpose of preparing such a study was to independently corroborate the findings of Maricopa County Air Quality Department (MCAQD) on source contribution estimates of VOC emissions as published in their 2020 Periodic Emissions Inventory for Ozone Precursors. The goal of preparing the findings in the study was to provide additional commentary on the significance of various VOC emissions sources to tropospheric ozone formation in Maricopa County through an alternate air quality modeling approach. The findings from this study are significant to the environment and health of Maricopa County as they offer additional insights into the pathways by which tropospheric ozone may form.

Identifying the airport as a key urban VOC source in the Pearl River Delta, China

Volatile organic compounds (VOCs) are the main precursors of ozone (O3) and secondary organic aerosol (SOA) formation in the atmosphere. The traditional positive matrix factorization (PMF) source apportionment method is mainly based on the time series of VOCs at a single site, and its results cannot indicate the difference spatially. In this study, a refined spatial distribution study was carried out in Shenzhen in the Pearl River Delta (PRD) region, China, with 110 sampling sites covering the city. Ninety-two VOC compounds were quantitatively analyzed and the spatial distribution characteristics of various VOCs were obtained. Based on the PMF source apportionment of multisite samples, five types of sources and their spatial distributions of vehicle exhaust, gasoline leakage, industrial processes, airport-related sources and regional transport were identified. The airport source was resolved for the first time in the VOC source apportionment and was further verified by the measured source spectra in the airport. It is found that the airport-related sources accounted for 19% of the ambient VOC concentrations in Shenzhen and had strong Cl radical reaction activity, indicating that the airport-related sources may have a greater impact on O3 and SOA formation in coastal cities than previously expected.

Influence of seasonal variability on source characteristics of VOCs at Houston industrial area

We studied the seasonal variations of volatile organic compounds (VOCs) in the Houston metropolitan area in the summertime and wintertime of 2018. The analysis of hourly measurements obtained from the automated gas chromatograph (auto-GC) network showed the total VOC average concentrations of 28.68 ppbC in the summertime and 33.81 ppbC in the wintertime. The largest contributions came from alkane compounds, which accounted for 61% and 82% of VOCs in the summer and winter, respectively. We performed principal component analysis (PCA) and Positive Matrix Factorization (PMF) and identified seven factors in the summertime and six factors in the wintertime, among which alkane species formed three factors according to their rate of reactions in both seasons: (1) the emissions of long-lived tracers from oil and natural gas (ONG long-lived species), (2) fuel evaporation, and (3) the emissions of short-lived tracers from oil and natural gas (ONG short-lived species). Two other similar factors were (4) emissions of aromatic compounds and (5) alkene species of ethylene and propylene. Summertime factor 6 was associated with acetylene, and one extra summertime factor 7 was influenced by the biogenic emissions. The factor 6 of wintertime was affected by vehicle exhaust. Higher nighttime and lower daytime values of the ethylene/acetylene ratios indicated a stronger rate of photochemical degradation during the summertime. Higher reactivities of alkenes and aromatics with radicals make seasonal differences of these compounds less variant. Also, the exploration of the photochemical processes of the VOCs showed that the ethylene and propylene had the highest contributions to the summertime and wintertime ozone formation as well as the emissions of the isoprene, which showed a high impact on summertime ozone. Our results acknowledged that ethylene and propylene continue to be significant emissions of VOCs, and their emissions control would help the mitigation of the ozone problem in downwind areas related to emissions at the Houston Ship Channel (HSC). Based on trajectory analysis, we localized the main VOC emission sources in HSC near local industrial areas and regions south of the HSC. Ambient concentrations of VOC in both seasons revealed compounds that measured at the HSC were influenced by the emissions from the petrochemical sectors and industrial complexes, especially from the Baytown refinery and Bayport industrial district next to the HSC and Galveston Bay refineries at the south of the study area.

Measurement report: High contributions of halocarbon and aromatic compounds to atmospheric volatile organic compounds in an industrial area

Abstract. Volatile organic compounds (VOCs) are key components of tropospheric chemistry. We investigated ambient VOCs in an industrial area in Nanjing, China, between July 2018 and May 2020. The sum of the suite of measured total VOC (TVOC) concentrations was 59.8 ± 28.6 ppbv (part per billion by volume) during the investigation period. About twice the TVOC concentrations were observed in the autumn (83 ± 20 ppbv) and winter (77.5 ± 16.8 ppbv) seasons compared to those in spring (39.6 ± 13.1 ppbv) and summer (38.8 ± 10.2 ppbv). In previous studies in Nanjing, oxygenated VOCs (OVOCs) and halocarbons were not measured, and the current TVOC concentration without halocarbons and OVOCs was similar to the previous investigation in the same study area. However, it was twofold higher than the one reported in the nonindustrial suburban area of Nanjing. Due to the industrial influence, the halocarbons VOC group (14.3 ± 7.3 ppbv, 24 %) was the second-largest contributor to the TVOCs after alkanes (21 ± 7 ppbv, 35 %), which is in contrast with the previous studies in Nanjing and also in almost all other regions in China. Relatively high proportions of halocarbons and aromatics were observed in autumn (25.7 % and 19.3 %, respectively) and winter (25.8 % and 17.6 %, respectively) compared to those in summer (20.4 % and 11.8 %, respectively) and spring (20.3 % and 13.6 %, respectively). According to the potential source contribution function (PSCF), short-distance transport from the surrounding industrial areas and cities was the main reason for the high VOC concentrations in the study area. According to positive matrix factorization (PMF) model results, vehicle-related emissions (33 %–48 %) contributed to the major portion of the ambient VOC concentrations. Aromatics, followed by alkenes, were the top contributors to the loss rate of OH radicals (LOH; 37 % and 32 %, respectively). According to the empirical kinetic modelling approach (EKMA) and relative incremental reactivity (RIR) analysis, the study area was in the VOC-sensitive regime for ozone (O3) formation during all measurement seasons. Therefore, alkenes and aromatics emissions from automobiles need to be decreased to reduce secondary air pollution formation in the study area.

Assessing volatile organic compound sources in a boreal forest using positive matrix factorization (PMF)

Ambient volatile organic compound (VOC) concentrations including individual monoterpenoids, sesquiterpenes (SQTs), isoprene, 2-methyl-3-buten-1-ol (MBO), methacrolein (MACR), C5–C10 aldehydes, benzene and toluene were measured in a coniferous forest in Hyytiälä, southern Finland, in April–November 2016 with 1–2 h time resolution. Positive matrix factorization (PMF) was used to resolve the major sources which were responsible for the observed ambient VOC concentrations. The most reliable results were obtained with a 10 factor solution including four anthropogenic and six biogenic sources. Three of the biogenic factors were induced by light. They were either light dependent emissions or products of photochemical reactions. Three factors appeared to be temperature dependent emissions. Biogenic emissions were clearly the most important source of the measured VOCs, but the contribution from a local sawmill was also significant. About half of the monoterpenes (MTs) could be appointed to Scots pine emissions, but the influence from the activities at a near-by sawmill and Norway spruce emissions were also found. In the case of some individual MTs (e.g. limonene), spruce emissions dominated. Spruce emissions were also mainly responsible for ambient SQTs, aldehydes, and isoprene. For anthropogenic compounds, benzene and toluene, background, and local activities were the main sources. PMF was useful in resolving the sources of ambient VOCs.

Volatile organic compounds and ozone air pollution in an oil production region in northern China

Abstract. Oil and natural gas (O&NG) exploration presents a significant source of atmospheric volatile organic compounds (VOCs), which are central players of tropospheric chemistry and contribute to formations of ozone (O3) and secondary organic aerosols. The impacts of O&NG extraction on regional air quality have been investigated in recent years in North America, but have long been overlooked in China. To assess the impacts of O&NG exploration on tropospheric O3 and regional air quality in China, intensive field observations were conducted during February–March and June–July 2017 in the Yellow River delta, an oil extraction region in northern China. Very high concentrations of ambient VOCs were observed at a rural site, with the highest alkane mixing ratios reaching 2498 ppbv. High-O3 episodes were not encountered during wintertime but were frequently observed in summer. The emission profiles of VOCs from the oil fields were directly measured for the first time in China. The chemical budgets of ROx radicals and O3 were dissected with a detailed chemical box model constrained by in situ observations. The highly abundant VOCs facilitated strong atmospheric oxidation capacity and O3 formation in the region. Oxygenated VOCs (OVOCs) played an essential role in the ROx primary production, OH loss, and radical recycling. Photolysis of OVOCs, O3, and HONO as well as ozonolysis reactions of unsaturated VOCs were major primary sources of ROx. NOx was the limiting factor of radical recycling and O3 formation. This study underlines the important impacts of O&NG extraction on atmospheric chemistry and regional air quality in China.

Composition of Clean Marine Air and Biogenic Influences on VOCs during the MUMBA Campaign

Volatile organic compounds (VOCs) are important precursors to the formation of ozone and fine particulate matter, the two pollutants of most concern in Sydney, Australia. Despite this importance, there are very few published measurements of ambient VOC concentrations in Australia. In this paper, we present mole fractions of several important VOCs measured during the campaign known as MUMBA (Measurements of Urban, Marine and Biogenic Air) in the Australian city of Wollongong (34°S). We particularly focus on measurements made during periods when clean marine air impacted the measurement site and on VOCs of biogenic origin. Typical unpolluted marine air mole fractions during austral summer 2012-2013 at latitude 34°S were established for CO2 (391.0 ± 0.6 ppm), CH4 (1760.1 ± 0.4 ppb), N2O (325.04 ± 0.08 ppb), CO (52.4 ± 1.7 ppb), O3 (20.5 ± 1.1 ppb), acetaldehyde (190 ± 40 ppt), acetone (260 ± 30 ppt), dimethyl sulphide (50 ± 10 ppt), benzene (20 ± 10 ppt), toluene (30 ± 20 ppt), C8H10 aromatics (23 ± 6 ppt) and C9H12 aromatics (36 ± 7 ppt). The MUMBA site was frequently influenced by VOCs of biogenic origin from a nearby strip of forested parkland to the east due to the dominant north-easterly afternoon sea breeze. VOCs from the more distant densely forested escarpment to the west also impacted the site, especially during two days of extreme heat and strong westerly winds. The relative amounts of different biogenic VOCs observed for these two biomes differed, with much larger increases of isoprene than of monoterpenes or methanol during the hot westerly winds from the escarpment than with cooler winds from the east. However, whether this was due to different vegetation types or was solely the result of the extreme temperatures is not entirely clear. We conclude that the clean marine air and biogenic signatures measured during the MUMBA campaign provide useful information about the typical abundance of several key VOCs and can be used to constrain chemical transport model simulations of the atmosphere in this poorly sampled region of the world.

Emission losses and dispersion of volatile organic compounds from tank farm of petroleum refinery complex.

Emission characteristics of volatile organic compounds (VOC) emitted from the tank farm of petroleum refinery were evaluated in this study in order to analyze for the potential impacts on health and odor nuisance problems. Estimation procedures were carried out by using the U.S.EPA TANK 4.0.9d emission model in conjunction with direct measurements of gas phase of each stored liquid within aboveground storage tanks. Results revealed that about 61.12% of total VOC emitted from the tank farm by volume were alkanes, in which pentane were richest (27.4%), followed by cyclopentane (19.22%), propene (19.02%), and isobutene (14.22%). Mostly of pentane (about 80%) were emitted from the floating roof tanks contained crude oil corresponded to the largest annual throughput of crude oil as compared with other petroleum distillates. Emission data were further analyzed for their ambient concentration using the AERMOD dispersion model in order to determine the extent and magnitude of odor and health impacts caused by pentane. Results indicated that there was no health impact from inhalation of pentane. However, predicted data were higher than the odor threshold values of pentane which indicated the possibility of odor nuisance problem in the vicinity areas of the refinery. In order to solve this problem, modification of the type of crude oil storage tanks from external floating roof to domed external floating roof could be significant success in reduction of both emissions and ambient concentrations of VOC from petroleum refinery tank farm.

The Spatiotemporal Response of Summertime Tropospheric Ozone to Changes in Local Precursor Emissions in the Lower Fraser Valley, British Columbia

ABSTRACTThis paper examines the spatiotemporal impact of changing local precursor emissions on a subset of air quality monitors in the coastal Lower Fraser Valley, British Columbia, Canada, over a 25-year period (1990–2014) marked by substantial emissions reductions. The analysis examines summertime (JJA) trends in ambient reactivity of volatile organic compounds (VOCs), , ozone, and odd oxygen (; defined as ) concentrations. To account for the potentially confounding influence of rising background ozone levels on the analysis, summer days are classified by whether appreciable local ozone production is likely or not, with a separate analysis undertaken for each set of conditions. The influence of short- and long-term meteorological variability, hebdomadal (weekly) emissions variability, and within-network spatial variability on long-term trends is accounted for by using Generalized Additive Models (GAM). The analysis suggests that long-term trends in local ambient VOC reactivity and concentrations have not occurred in a uniform fashion nor have they changed in a synchronized way. Declines in VOC reactivity appear to have occurred sooner and at a more uniform rate, but concentrations appear to have remained constant for the first 10 years before rapidly declining. Similarly, we find ozone reductions have not occurred uniformly in time nor has the network response been spatially uniform, with the smallest reductions occurring just downwind of the region's downtown core and the largest reductions about 40 km further downwind. Much of the non-uniformity in response can be attributed to changing odd-oxygen partitioning rather than changing ozone production. During our analysis period, ozone concentrations during days not conducive to ozone photochemistry appear to have increased at a rate consistent with previous background trend analyses over western North America. We use the difference between ozone concentrations on fair-weather summer days and days with little photochemistry to build a response surface for “net-produced” ozone as a function of meteorologically controlled ambient VOC reactivity and concentrations. We find that much of the predicted behaviour in local ambient ozone can be understood in light of VOC-limited conditions and differing rates of local VOC and emissions reductions. It appears that these precursor reductions have largely resulted from evolving light-duty emission control technologies and local fleet turnover.

Quantification of the Influence of Industrial Emissions on Volatile Organic Compounds (VOCs) Using PMF Model: A Case Study of Jiangbei Industrial Zone in Nanjing

Volatile organic compounds(VOCs)are important precursors of ozone and secondary organic aerosol. The effect of industrial emissions on ambient VOC concentrations in the Jiangbei Industrial Zone in Nanjing was evaluated using the ambient VOCs measurements taken at Nanjing University of Information Science and Technology (NUIST) during March 2017. The monitoring data showed that the sum of 92 measured VOCs (TVOCs) ranged from 10.3×10-9 to 200.5×10-9. Some VOC species, such as ethylene, propene, benzene, styrene, and dichloromethane had abnormally high values. Positive matrix factorization model (PMF) was used to identify the main sources of VOCs. The results showed that industrial emissions on average accounted for 50.0% of TVOCs, while petrochemical industry, chemical industry, and paints & solvents use accounted for 14.9%, 19.3% and 15.8%, respectively. During a VOC pollution episode, the contribution of industrial emissions reached 74.9%. The direction of industrial sources was determined by combining the wind speed and wind direction data.

Pilot study investigating ambient air toxics emissions near a Canadian kraft pulp and paper facility in Pictou County, Nova Scotia.

Air toxics are airborne pollutants known or suspected to cause cancer or other serious health effects, including certain volatile organic compounds (VOCs), prioritized by the US Environmental Protection Agency (EPA). While several EPA-designated air toxics are monitored at a subset of Canadian National Air Pollution Surveillance (NAPS) sites, Canada has no specific "air toxics" control priorities. Although pulp and paper (P&P) mills are major industrial emitters of air pollutants, few studies quantified the spectrum of air quality exposures. Moreover, most NAPS monitoring sites are in urban centers; in contrast, rural NAPS sites are sparse with few exposure risk records. The objective of this pilot study was to investigate prioritized air toxic ambient VOC concentrations using NAPS hourly emissions data from a rural Pictou, Nova Scotia Kraft P&P town to document concentration levels, and to determine whether these concentrations correlated with wind direction at the NAPS site (located southwest of the mill). Publicly accessible Environment and Climate Change Canada data (VOC concentrations [Granton NAPS ID: 31201] and local meteorological conditions [Caribou Point]) were examined using temporal (2006-2013) and spatial analytic methods. Results revealed several VOCs (1,3-butadiene, benzene, and carbon tetrachloride) routinely exceeded EPA air toxics-associated cancer risk thresholds. 1,3-Butadiene and tetrachloroethylene were significantly higher (p<0.05) when prevailing wind direction blew from the northeast and the mill towards the NAPS site. Conversely, when prevailing winds originated from the southwest towards the mill, higher median VOC air toxics concentrations at the NAPS site, except carbon tetrachloride, were not observed. Despite study limitations, this is one of few investigations documenting elevated concentrations of certain VOCs air toxics to be associated with P&P emissions in a community. Findings support the need for more research on the extent to which air toxics emissions exist in P&P towns and contribute to poor health in nearby communities.

Spatiotemporal description of BTEX volatile organic compounds in a Middle Eastern megacity: Tehran Study of Exposure Prediction for Environmental Health Research (Tehran SEPEHR)

The spatiotemporal variability of ambient volatile organic compounds (VOCs) in Tehran, Iran, is not well understood. Here we present the design, methods, and results of the Tehran Study of Exposure Prediction for Environmental Health Research (Tehran SEPEHR) on ambient concentrations of benzene, toluene, ethylbenzene, p-xylene, m-xylene, o-xylene (BTEX), and total BTEX. To date, this is the largest study of its kind in a low- and middle-income country and one of the largest globally. We measured BTEX concentrations at five reference sites and 174 distributed sites identified by a cluster analytic method. Samples were taken over 25 consecutive 2-weeks at five reference sites (to be used for temporal adjustments) and over three 2-week campaigns in summer, winter, and spring at 174 distributed sites. The annual median (25th–75th percentile) for benzene, the most carcinogenic of the BTEX species, was 7.8 (6.3–9.9) μg/m3, and was higher than the national and European Union air quality standard of 5 μg/m3 at approximately 90% of the measured sites. The estimated annual mean concentrations of BTEX were spatially highly correlated for all pollutants (Spearman rank coefficient 0.81–0.98). In general, concentrations and spatial variability were highest during the summer months, most likely due to fuel evaporation in hot weather. The annual median of benzene and total BTEX across the 35 sites in the Tehran regulatory monitoring network (7.7 and 56.8 μg/m3, respectively) did a reasonable job of approximating the additional 144 city-wide sites (7.9 and 58.7 μg/m3, respectively). The annual median concentrations of benzene and total BTEX within 300 m of gas stations were 9.1 and 67.3 μg/m3, respectively, and were higher than sites outside this buffer. We further found that airport did not affect annual BTEX concentrations of sites within 1 km. Overall, the observed ambient concentrations of toxic VOCs are a public health concern in Tehran.

Seasonal variability and source apportionment of volatile organic compounds (VOCs) in the Paris megacity (France)

Abstract. Within the framework of air quality studies at the megacity scale, highly time-resolved volatile organic compound (C2–C8) measurements were performed in downtown Paris (urban background sites) from January to November 2010. This unique dataset included non-methane hydrocarbons (NMHCs) and aromatic/oxygenated species (OVOCs) measured by a GC-FID (gas chromatograph with a flame ionization detector) and a PTR-MS (proton transfer reaction – mass spectrometer), respectively. This study presents the seasonal variability of atmospheric VOCs being monitored in the French megacity and their various associated emission sources. Clear seasonal and diurnal patterns differed from one VOC to another as the result of their different origins and the influence of environmental parameters (solar radiation, temperature). Source apportionment (SA) was comprehensively conducted using a multivariate mathematical receptor modeling. The United States Environmental Protection Agency's positive matrix factorization tool (US EPA, PMF) was used to apportion and quantify ambient VOC concentrations into six different sources. The modeled source profiles were identified from near-field observations (measurements from three distinct emission sources: inside a highway tunnel, at a fireplace and from a domestic gas flue, hence with a specific focus on road traffic, wood-burning activities and natural gas emissions) and hydrocarbon profiles reported in the literature. The reconstructed VOC sources were cross validated using independent tracers such as inorganic gases (NO, NO2, CO), black carbon (BC) and meteorological data (temperature). The largest contributors to the predicted VOC concentrations were traffic-related activities (including motor vehicle exhaust, 15 % of the total mass on the annual average, and evaporative sources, 10 %), with the remaining emissions from natural gas and background (23 %), solvent use (20 %), wood-burning (18 %) and a biogenic source (15 %). An important finding of this work is the significant contribution from wood-burning, especially in winter, where it could represent up to ∼ 50 % of the total mass of VOCs. Biogenic emissions also surprisingly contributed up to ∼ 30 % in summer (due to the dominating weight of OVOCs in this source). Finally, the mixed natural gas and background source exhibited a high contribution in spring (35 %, when continental air influences were observed) and in autumn (23 %, for home heating consumption).

Ambient volatile organic compounds pollution in China

Owing to rapid economic and industrial development, China has been suffering from degraded air quality and visibility. Volatile organic compounds (VOCs) are important precursors to the formation of ground-level ozone and hence photochemical smog. Some VOCs adversely affect human health. Therefore, VOCs have recently elicited public concern and given new impetus to scientific interest. China is now implementing a series of polices to control VOCs pollution. The key to formulating policy is understanding the ambient VOCs pollution status. This paper mainly analyzes the species, levels, sources, and spatial distributions of VOCs in ambient air. The results show that the concentrations of ambient VOCs in China are much higher than those of developed countries such as the United States and Japan, especial benzene, which exceeds available standards. At the same time, the ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) of various VOCs are calculated. Aromatics and alkenes have much higher OFPs, while aromatics have higher SOAFP. The OFPs of ambient VOCs in the cities of Beijing, Guangzhou and Changchun are very high, and the SOAFP of ambient VOCs in the cities of Hangzhou, Guangzhou and Changchun are higher.

VOCs emission rate estimate for complicated industrial area source using an inverse-dispersion calculation method: A case study on a petroleum refinery in Northern China

This study aimed to apply an inverse-dispersion calculation method (IDM) to estimate the emission rate of volatile organic compounds (VOCs) for the complicated industrial area sources, through a case study on a petroleum refinery in Northern China. The IDM was composed of on-site monitoring of ambient VOCs concentrations and meteorological parameters around the source, calculation of the relationship coefficient γ between the source's emission rate and the ambient VOCs concentration by the ISC3 model, and estimation of the actual VOCs emission rate from the source. Targeting the studied refinery, 10 tests and 8 tests were respectively conducted in March and in June of 2014. The monitoring showed large differences in VOCs concentrations between background and downwind receptors, reaching 59.7 ppbv in March and 248.6 ppbv in June, on average. The VOCs increases at receptors mainly consisted of ethane (3.1%–22.6%), propane (3.8%–11.3%), isobutane (8.5%–10.2%), n-butane (9.9%–13.2%), isopentane (6.1%–12.9%), n-pentane (5.1%–9.7%), propylene (6.1–11.1%) and 1-butylene (1.6%–5.4%). The chemical composition of the VOCs increases in this field monitoring was similar to that of VOCs emissions from China's refineries reported, which revealed that the ambient VOCs increases were predominantly contributed by this refinery. So, we used the ISC3 model to create the relationship coefficient γ for each receptor of each test. In result, the monthly VOCs emissions from this refinery were calculated to be 183.5 ± 89.0 ton in March and 538.3 ± 281.0 ton in June. The estimate in June was greatly higher than in March, chiefly because the higher environmental temperature in summer produced more VOCs emissions from evaporation and fugitive process of the refinery. Finally, the VOCs emission factors (g VOCs/kg crude oil refined) of 0.73 ± 0.34 (in March) and 2.15 ± 1.12 (in June) were deduced for this refinery, being in the same order with previous direct-measurement results (1.08–2.65 g VOCs/kg crude oil refined).An inverse-dispersion calculation method was applied to estimate VOCs emission rate for a petroleum refinery, being 183.5 ton/month (March) and 538.3 ton/month (June).

Adjoint-based computation of U.S. nationwide ozone exposure isopleths

Population exposure to daily maximum ozone is associated with an increased risk of premature mortality, and efforts to mitigate these impacts involve reducing emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs). We quantify the dependence of U.S. national exposure to annually averaged daily maximum ozone on ambient VOC and NOx concentrations through ozone exposure isopleths, developed using emissions sensitivities from the adjoint of the GEOS-Chem air quality model for 2006. We develop exposure isopleths for all locations within the contiguous US and derive metrics based on the isopleths that quantify the impact of emissions on national ozone exposure. This work is the first to create ozone exposure isopleths using adjoint sensitivities and at a large scale. We find that across the US, 29% of locations experience VOC-limited conditions (where increased NOx emissions lower ozone) during 51% of the year on average. VOC-limited conditions are approximately evenly distributed diurnally and occur more frequently during the fall and winter months (67% of the time) than in the spring and summer (37% of the time). The VOC/NOx ratio of the ridge line on the isopleth diagram (denoting a local maximum in ozone exposure with respect to NOx concentrations) is 9.2 ppbC/ppb on average across grid cells that experience VOC-limited conditions and 7.9, 10.1 and 6.7 ppbC/ppb at the three most populous US cities of New York, Los Angeles and Chicago, respectively. Emissions that are ozone exposure-neutral during VOC-limited exposure conditions result in VOC/NOx concentration ratios of 0.63, 1.61 and 0.72 ppbC/ppb at each of the three US cities respectively, and between 0.01 and 1.91 ppbC/ppb at other locations. The sensitivity of national ozone exposure to NOx and VOC emissions is found to be highest near major cities in the US. Together, this information can be used to assess the effectiveness of NOx and VOC emission reductions on mitigating ozone exposure in the US, determine where they will be counterproductive, and quantify the optimal NOx/VOC reduction ratio.

Twelve-year trends in ambient concentrations of volatile organic compounds in a community of the Alberta Oil Sands Region, Canada

Environmental exposure to volatile organic compounds (VOCs) in ambient air is one of a number of concerns that the First Nation Community of Fort McKay, Alberta has related to development of Canada's oil sands. An in-depth investigation of trends in ambient air VOC levels in Fort McKay was undertaken to better understand the role and possible significance of emissions from Alberta's oil sands development. A non-parametric trend detection method was used to investigate trends in emissions and ambient VOC concentrations over a 12-year (2001−2012) period. Relationships between ambient VOC concentrations and production indicators of oil sands operations around Fort McKay were also examined. A weak upward trend (significant at 90% confidence level) was found for ambient concentrations of total VOCs based on sixteen detected species with an annual increase of 0.64μg/m3 (7.2%) per year (7.7μg/m3 increase per decade). Indicators of production (i.e., annual bitumen production and mined oil sands quantities) were correlated with ambient total VOC concentrations. Only one of 29 VOC species evaluated (1-butene) showed a statistically significant upward trend (p=0.05). Observed geometric (arithmetic) mean and maximum ambient concentrations of selected VOCs of public health concern for most recent three years of the study period (2010−2012) were below chronic and acute health risk screening criteria of the U.S. Agency for Toxic Substances and Disease Registry and U.S. Environmental Protection Agency. Thirty-two VOCs are recommended for tracking in future air quality investigations in the community to better understand whether changes are occurring over time in relation to oil sands development activities and to inform policy makers about whether or not these changes warrant additional attention.

Trends in selected ambient volatile organic compound (VOC) concentrations and a comparison to mobile source emission trends in California's South Coast Air Basin

Abstract Trends in ambient concentrations of Volatile Organic Compounds (VOC) in the South Coast Air Basin (SoCAB) are compared to trends in VOC emissions from Light-Duty Gasoline Vehicles (LDGV) tested on chassis dynamometers and to trends observed in tunnel studies during the same period to understand the impacts of gasoline vehicle emissions on ambient VOC concentrations from 1999 to 2009. Annual median concentrations for most ambient VOCs decreased 40% from 1999 to 2009 in the SoCAB, based on data from the Photochemical Assessment Monitoring Stations (PAMS). Annual concentration decreases of most compounds, except 2,2,4-trimethylpentane, are highly correlated with the decrease of acetylene, a marker for tailpipe emissions from LDGV. This indicates that ambient VOC concentration decreases were likely due to tailpipe emission reductions from gasoline vehicles. Air Toxics Monitoring Network data also support this conclusion. Benzene concentration-normalized ratios for most compounds except ethane, propane, isoprene, and 2,2,4-trimethylpentane were stable even as these compound concentrations decreased significantly from 1999 to 2009. Such stability suggests that the main sources of ambient VOC were still the same from 1999 to 2009. The comparison of trends in dynamometer testing and tunnel studies also shows that tailpipe emissions remained the dominant source of tunnel LDGV emissions. The pronounced changes in 2,2,4-trimethylpentane ratios due to the introduction of Phase 3 gasoline also confirm the substantial impact of LDGV emissions on ambient VOCs. Diurnal ambient VOC data also suggest that LDGV tailpipe emissions remained the dominant source of ambient VOCs in the SoCAB in 2009. Our conclusion, which is that current inventory models underestimate VOC emissions from mobile sources, is consistent with that of several recent studies of ambient trends in the SoCAB. Our study showed that tailpipe emissions remained a bigger contributor to ambient VOCs than evaporative emissions from LDGV's. This finding is also different from EMFAC estimates.