Ambient Concentrations Of Volatile Organic Compounds Research Articles

Exposure to volatile organic compounds and associated health risks in windsor, Canada

ObjectiveWe examined relationships among measurements of volatile organic compounds (VOCs) and performed cancer and non-cancer risk assessments to determine potential adverse health effects. MethodsPersonal, indoor and outdoor concentrations of VOCs were measured for 50 non-smoking adults in Windsor, Ontario during winter and summer 2005. The potential excess cancer cases associated with personal concentration were estimated by the Inhalation Unit Risk (USEPA IRIS) and Tumorigenic Concentration (Health Canada). Inhalation Reference Concentration (RfC) was used to evaluate non-cancer adverse effects. Indoor and personal concentrations were statistically compared. Correlations of personal concentrations were estimated to investigate the associations among VOCs. ResultsEstimated median lifetime excess cancer risks (95th percentile upper-bound) of benzene and 1,3-butadiene were 8.09 and 4.77 per 1 million. Acetaldehyde presented the highest non-cancer risk. For some VOCs, the personal and indoor geometric means were similar, but arithmetic personal means were higher than the arithmetic indoor means (p < 0.05). Negative correlations among personal VOC concentrations were not sizable. ConclusionEvaluation of potential cancer and non-cancer risks from VOCs at the personal level should not rely merely on ambient (indoor and outdoor) VOC concentrations. Our analysis showed that personal risk had a complicated pattern that needs further investigation. Our results can be used to prioritize mitigation strategies to protect human health.

Spatial and temporal variations in atmospheric VOCs, NO2, SO2, and O3 concentrations at a heavily industrialized region in Western Turkey, and assessment of the carcinogenic risk levels of benzene

Ambient concentrations of volatile organic compounds (VOCs), nitrogen dioxide (NO2), sulphur dioxide (SO2) and ground-level ozone (O3) were measured at 55 locations around a densely populated industrial zone, hosting a petrochemical complex (Petkim), a petroleum refinery (Tupras), ship-dismantling facilities, several iron and steel plants, and a gas-fired power plant. Five passive sampling campaigns were performed covering summer and winter seasons of 2005 and 2007. Elevated concentrations of VOCs, NO2 and SO2 around the refinery, petrochemical complex and roads indicated that industrial activities and vehicular emissions are the main sources of these pollutants in the region. Ozone concentrations were low at the industrial zone and settlement areas, but high in rural stations downwind from these sources due to NO distillation. The United States Environmental Protection Agency's positive matrix factorization receptor model (EPA PMF) was employed to apportion ambient concentrations of VOCs into six factors, which were associated with emissions sources. Traffic was found to be highest contributor to measured ∑VOCs concentrations, followed by the Petkim and Tupras.Median cancer risk due to benzene inhalation calculated using a Monte Carlo simulation was approximately 4 per-one-million population, which exceeded the U.S. EPA benchmark of 1 per one million. Petkim, Tupras and traffic emissions were the major sources of cancer risk due to benzene inhalation in the Aliaga airshed. Relative contributions of these two source groups changes significantly from one location to another, demonstrating the limitation of determining source contributions and calculating health risk using data from one or two permanent stations in an industrial area.

Air Pollution and Biological Exposure near Petrochemical Industrial Complex

Yeosu(southern coastal region, Repubulic of Korea) industrial complex has produced a majority of petrochemical products since 1979. In spite of a huge industrial growth during the last 4 decades, there has been a heavy environmental pollution in the surrounding areas. As the public are worried about their environmental health status, this study investigated the air pollution and biological exposure in the surrounding areas of industrial complex. Volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) were monitored at 10 sites in the residential areas by distance from the petrochemical complex. Biological exposure was assessed using questionnaire, and urine and blood samples of 600 residents. Ambient concentrations of VOCs and PAHs in the surrounding area were higher when compared to those of the area far from the industrial complex. The concentration of benzene (2.01 ppb) in several areas exceeded the annual standard (1.5 ppb). The geometric mean levels of urinary metabolites of all VOCs and PAHs, such as t,t-muconic acid, hippuric acid, methylhippuric acid, phenylglyoxlic acid, mandelic acid, 1-hydroxypyrene, 2-naphthol, 2-hydroxyfluorene, and 1-hydroxyphenanthrene in the residents living nearby were 45.17, 213.34(mg/g-cr), 307.38, 284.05, 303.30, 0.22, 4.74, 0.36, and 0.41 ug/g-cr, respectively, whereas those of residents far from the petrochemical industrial complex were 39.49, 197.86(mg/g-cr), 298.46, 228.06, 252.32, 0.21, 3.83, 0.25, and 0.16 ug/g-cr, respectively. Multi-regression analysis showed that residential region, gender, and smoking habit contributed to the concentrations of pollutants in urine and blood. The ratio of diagnostic experience on the chronic and acute disease such as diabetes, asthma, COPD, and allergic disease in questionnaire (about 30 diseases) did not show statistically significant relationship between regions.

Impact of emissions from natural gas production facilities on ambient air quality in the Barnett Shale area: A pilot study

Rapid and extensive development of shale gas resources in the Barnett Shale region of Texas in recent years has created concerns about potential environmental impacts on water and air quality. The purpose of this study was to provide a better understanding of the potential contributions of emissions from gas production operations to population exposure to air toxics in the Barnett Shale region. This goal was approached using a combination of chemical characterization of the volatile organic compound (VOC) emissions from active wells, saturation monitoring for gaseous and particulate pollutants in a residential community located near active gas/oil extraction and processing facilities, source apportionment of VOCs measured in the community using the Chemical Mass Balance (CMB) receptor model, and direct measurements of the pollutant gradient downwind of a gas well with high VOC emissions. Overall, the study results indicate that air quality impacts due to individual gas wells and compressor stations are not likely to be discernible beyond a distance of approximately 100 m in the downwind direction. However, source apportionment results indicate a significant contribution to regional VOCs from gas production sources, particularly for lower-molecular-weight alkanes (<C6). Although measured ambient VOC concentrations were well below health-based safe exposure levels, the existence of urban-level mean concentrations of benzene and other mobile source air toxics combined with soot to total carbon ratios that were high for an area with little residential or commercial development may be indicative of the impact of increased heavy-duty vehicle traffic related to gas productionImplicationsRapid and extensive development of shale gas resources in recent years has created concerns about potential environmental impacts on water and air quality. This study focused on directly measuring the ambient air pollutant levels occurring at residential properties located near natural gas extraction and processing facilities, and estimating the relative contributions from gas production and motor vehicle emissions to ambient VOC concentrations. Although only a small-scale case study, the results may be useful for guidance in planning future ambient air quality studies and human exposure estimates in areas of intensive shale gas production.

Spatial and seasonal variation and source apportionment of volatile organic compounds (VOCs) in a heavily industrialized region

Source apportionment is generally applied to a time series of pollutant concentrations measured at a single site. However, in a complex airshed having multiple pollutant sources, it may be helpful to collect samples from several sites to ensure that some of them have low contributions from specific sources. Ambient air samples (n = 160) were collected by passive sampling during four seasons in 2009 and 2010 at forty different sites in Aliaga, Turkey to determine the spatial, seasonal variations and possible sources of volatile organic compounds (VOCs). Fifty-eight VOCs (Σ58VOC) were detected. Σ58VOC concentrations ranged between 0.1 and 1770 μg m−3 (avg ± SD, 67 ± 193 μg m−3). Aliphatic hydrocarbons were generally predominant with a high percentage of contribution (31%–88%) at all sites. Aromatic VOCs were the second highest group (8–50%), followed by halogenated VOCs (1–24%) and oxygenated VOCs (0.04–5.9%). Highly variable spatial distribution of ambient VOC concentrations suggested that the major sources in this region were industrial plants. Generally, VOC concentrations were higher in summer than in winter probably due to increased volatilization from their sources at higher ambient temperatures. However, high atmospheric VOC concentrations were also observed in winter and fall near the petroleum refinery and petrochemical complex, probably due to the calm conditions and high atmospheric stability that is commonly encountered during the winter months in the area, restricting the dilution of pollutants. The newest version of EPA PMF (V5.0) (Positive Matrix Factorization) having the capability of handling multiple site data was used for source apportionment. Refinery and petroleum products, petrochemical industry, solvent use and industrial processes, and vehicle exhaust were the identified VOC sources in the study area, contributing 56%, 22%, 12%, and 10%, respectively to the Σ58VOC concentrations. Carcinogenic risks due to lifetime exposure to seven VOCs were also estimated. Estimated risks were the highest for 1,2-dichloroethane, followed by benzene, chloroform, and carbon tetrachloride. Carcinogenic risks for trichloroethene, 1,1,2-trichloroethane, and bromoform were lower than the general acceptable risk level of 1.0 × 10−6. However, risks for 1,2-dichloroethane, benzene, chloroform, and carbon tetrachloride were substantially higher than the acceptable level. It was concluded that carcinogenic risks may reach considerably high levels for a significant portion of the population living in the study area.

Seasonal and Temporal Variation of Volatile Organic Compounds (VOCs) Pollution in Isolo Industrial Areas of Lagos State, Southwestern-Nigeria

Spatial and temporal variations of volatile organic compounds in ambient air in Isolo Industrial Area during May, 2010 to April, 2011 are presented. The results were analysed in other to present information about the detailed nature of air quality situation in the sampled areas. The air samples were collected by passive sampler (ORSA 5). The air samplers were exposed to a height of 1.5 - 2.0 m and sampling was carried out four times a month for a period of 12 months. The adsorbed VOCs were desorbed with carbondisulphide (CS 2 ) and the solution analysed using Gas Chromatography (GC) fitted with Flame Ionization Detector (FID). The results from analysis of the air samples collected showed that twenty (26) VOCs were captured. There is a significant difference (P < 0.05) between the levels of VOCs in Isolo. Despite comparatively higher concentrations of VOCs at the studied sites, there is a significant difference in the spatial distribution. At lower wind speed, the VOCs concentrations tend to increase and become uniformly distributed around the industrial Areas. The temporal distribution shows a decrease in ambient concentrations of VOCs from May to July due to Atmospheric (dilution)/wash down by rain. The results of two-way factor ANOVA analysis of the monthly average of total volatile organic compounds revealed that there is significant difference (P < 0.05) in seasonal and temporal variations of TVOC concentrations in the studied areas. The meteorological parameters showed significant correlations with the ambient concentrations of VOCs. The principal component analysis revealed that the major sources of VOCs in Isolo are mainly Anthropogenic and four (4) factors were identified as sources of VOCs in the studied area with Industrial and emissions from traffic dominating. Key words: Significant, Pollution, Spatial, Anthropogenic, Temporal

Ambient Volatile Organic Compounds (VOCs) pollution in Isolo Industrial Area of Lagos State, Southwestern – Nigeria

Air pollution by volatile organic compounds is based on the principles of dilution, diffusion and dispersion. The air samples were collected by passive sampler (ORSA 5). The air samplers were exposed to a height of 1.5 - 2.0 m and sampling was carried out four times a month for a period of 12 months. The adsorbed VOCs were desorbed with carbondisulphide (CS2) and the solution analysed using Gas Chromatography (GC) fitted with Flame Ionization Detector (FID). The results from analysis of the air samples collected showed that twenty-six (26) VOCs were captured in Isolo Industrial area. The VOCs were classified thus: aromatics 41%, halogenated 42%, esters 3%, ketones 8%, alcohols 4%, and ethers 2%. There is a significant difference (P &lt; 0.05) between the levels of VOCs in Isolo Industrial area. The meteorological parameters showed significant correlations with the ambient concentrations of VOCs. The principal component analysis revealed that the major sources of VOCs in the industrial area are mainly anthropogenic. Evaporative, vehicular/petroleum product, solvent and Industrial emission were identified as sources of VOCs in the studied industrial area with industrial emissions dominating.Keywords: Pollution, Ambient, Gas Chromatography, Industrial, Anthropogenic.

Source apportionment of volatile organic compounds measured in Edmonton, Alberta

From 2003 to 2009, whole air samples were collected at two sites in Edmonton and analyzed for over 77 volatile organic compounds (VOCs). VOCs were sampled in the downtown area (Central site) and an industrial area on the eastern side of the city (East site). Concentrations of most VOCs were highest at the East site, with an average total VOC mass concentration of 221 μg m−3. The average total VOC mass concentration at the Central site was 65 μg m−3. The United States Environmental Protection Agency's positive matrix factorization receptor model (EPA PMF) was used to apportion ambient concentrations of VOCs into eleven factors, which were associated with emissions sources. On average, 94 and 99% of the measured mass were apportioned by PMF at the East and Central site, respectively. Factors include transportation combustion (gasoline and diesel), industrial sources (industrial evaporative, industrial feedstock, gasoline production/storage, industrial chemical use), mixed mobile and industrial (gasoline evaporative, fugitive butane), a biogenic source, a natural gas related source, and a factor that was associated with global background pollutants transported into the area. Transportation sources accounted for more than half of the reconstructed VOC mass concentration at the Central site, but less than 10% of the reconstructed mass concentration at the East site. By contrast, industrial sources accounted for ten times more of the reconstructed VOC mass concentration at the East site than at the Central site and were responsible for approximately 75% of the reconstructed VOC mass concentration observed at the East site. Of the six industrial factors identified at the East site, four were linked to petrochemical industry production and storage. The two largest contributors to the reconstructed VOC mass concentration at the East site were associated with fugitive emissions of volatile species (butanes, pentanes, hexane, and cyclohexane); together, these two factors accounted for more than 50% of the reconstructed VOC mass concentration at the East site in contrast to less than 2% of the reconstructed mass concentration at the Central site. Natural gas related emissions accounted for 10%–20% of the reconstructed mass concentration at both sites. Biogenic emissions and VOCs associated with well-mixed global background were less than 10% of the reconstructed VOC mass concentration at the Central site and less than 3% of the reconstructed mass concentration at the East site.

A cohort study of intra-urban variations in volatile organic compounds and mortality, Toronto, Canada

This study investigated associations between long-term exposure to ambient volatile organic compounds (VOCs) and mortality. 58,760 Toronto residents (≥35 years of age) were selected from tax filings and followed from 1982 to 2004. Death information was extracted using record linkage to national mortality data. Land-use regression surfaces for benzene, n-hexane, and total hydrocarbons were generated from sampling campaigns in 2002 and 2004 and assigned to residential addresses in 1982. Cox regression was used to estimate relationships between each VOC and non-accidental, cardiovascular, and cancer mortality. Positive associations were observed for each VOC. In multi-pollutant models the benzene and total hydrocarbon signals were strongest for cancer. The hazard ratio for cancer that corresponded to an increase in the interquartile range of benzene (0.13 μg/m3) was 1.06 (95% CI = 1.02–1.11). Our findings suggest ambient concentrations of VOCs were associated with cancer mortality, and that these exposures did not confound our previously reported associations between NO2 and cardiovascular mortality.

Source Apportionment of Volatile Organic Compounds in Tehran, Iran

Identifying the sources of volatile organic compounds (VOCs) is key issue to reducing ground-level ozone and PAN. A multivariate receptor model (Unmix) was used for the determination of the contributions of VOCs sources in Tehran-Iran. Concentrations of ambient C2-C10 VOCs were measured continuously and online at the center of Tehran city during the winter of 2012. A high correlation coefficient existed between measured and predicted values (R (2) = 0.99), indicating that the data were well modeled. Five possible VOCs source categories were identified and mobile sources such as vehicle exhaust (61 %) and fuel evaporation (12 %) more than half of the total VOC concentration. City gas and CNG sources, biogenic source, and industrial solvent source categories accounted for 17 %, 8 % and 2 % of the total VOC, respectively. Result showed Unmix for VOCs source apportionment can be used to analyze and generate air pollution control strategies and policies.

Characteristics of Ambient Volatile Organic Compounds (VOCs) Measured in Shanghai, China

To better understand the characteristics of ambient abundance of volatile organic compounds (VOCs) in Shanghai, one of the biggest metropolis of China, VOCs were measured with a gas chromatography system equipped with a mass-selective detector (GC/MSD) from July 2006 to February 2010. An intensive measurement campaign was conducted (eight samples per day with a 3 hour interval) during May 2009. The comparison of ambient VOCs collected in different regions of Shanghai shows that the concentrations are slightly higher in the busy commercial area (28.9 ppbv at Xujiaui) than in the urban administrative area (24.3 ppbv at Pudong). However, during the intensive measurement period, the concentrations in the large steel industrial area (28.7 ppbv at Baoshan) were much higher than in the urban administrative area (18 ppbv at Pudong), especially for alkanes, alkenes, and toluene. The seasonal variations of ambient VOC concentrations measured at the Xujiahui sampling site indicate that the VOC concentrations are significantly affected by meteorological conditions (such as wind direction and precipitation). In addition, although alkanes are the most abundant VOCs at the Xujiahui measurement site, the most important VOCs contributing to ozone formation potential (OFP) are aromatics, accounting for 57% of the total OFP. The diurnal variations of VOC concentrations show that VOC concentrations are higher on weekdays than in weekends at the Xujiahui sampling site, suggesting that traffic condition and human activities have important impacts on VOC emissions in Shanghai. The evidence also shows that the major sources of isoprene are mainly resulted from gasoline evaporation at a particular time (06:00–09:00) in the busy commercial area. The results gained from this study provide useful information for better understanding the characteristics of ambient VOCs and the sources of VOCs in Shanghai.

A land use regression model for predicting ambient volatile organic compound concentrations in Toronto, Canada

More than 25 studies have employed land use regression (LUR) models to estimate nitrogen oxides and to a lesser extent particulate matter indicators, but these methods have been less commonly applied to ambient concentrations of volatile organic compounds (VOCs). Some VOCs have high plausibility as sources of health effects and others are specific indicators of motor vehicle exhaust. We used LUR models to estimate spatial variability of VOCs in Toronto, Canada. Benzene, n-hexane and total hydrocarbons (THC) were measured from July 25 to August 9, 2006 at 50 locations using the TraceAir organic vapor monitors. Nitrogen dioxide (NO 2) was also sampled to assess its spatial pattern agreement with VOC exposures. Buffers for land use, population density, traffic density, physical geography, and remote sensing measures of greenness and surface brightness were also tested. The remote sensing measures have the highest correlations with VOCs and NO 2 levels (i.e., explains >36% of the variance). Our regression models explain 66–68% of the variance in the spatial distribution of VOCs, compared to 81% for the NO 2 model. The ranks of agreement between various VOCs range from 48 to 63% and increases substantially – up to 75% – for the top and bottom quartile groups. Agreements between NO 2 and VOCs are much smaller with an average rank of 36%. Future epidemiologic studies may therefore benefit from using VOCs as potential toxic agents for traffic-related pollutants.

Ambient levels of volatile organic compounds in the vicinity of petrochemical industrial area of Yokohama, Japan.

Urban ambient air concentrations of 39 aromatic (including benzene, toluene, and xylenes) and aliphatic volatile organic compounds (VOCs) were measured in Yokohama city, Japan. Yokohama city was selected as a case study to assess the amount of VOC released from Industrial area to characterize the ambient air quality with respect to VOC as well as to know the impact of petrochemical storage facilities on local air quality. For this purpose, ambient air samples were collected (from June 2007 to November 2008) at six selected locations which are designated as industrial, residential, or commercial areas. To find out the diurnal variations of VOC, hourly nighttime sampling was carried out for three nights at one of the industrial locations (Shiohama). Samples were analyzed using gas chromatographic system (GC-FID). Results show strong variation between day and nighttime concentrations and among the seasons. Aliphatic fractions were most abundant, suggesting petrochemical storage facilities as the major source of atmospheric hydrocarbons. High concentrations of benzene, toluene, ethyl benzene, and xylene (BTEX) were observed at industrial locations. BTEX showed strong diurnal variation which is attributed to change in meteorology. During our campaign, low ambient VOC concentrations were observed at the residential site.

Landfill gas emission prediction using Voronoi diagrams and importance sampling

Municipal solid waste (MSW) landfills are among the nation's largest emitters of methane, a key greenhouse gas, and there is considerable interest in quantifying the surficial methane emissions from landfills. There are limitations in obtaining accurate emissions data by field measurements, and in characterizing an entire landfill with only a few such emissions measurements. This paper proposes an emissions prediction approach using numerous ambient air volatile organic compound (VOC) measurements above the surface of a landfill that are more easily obtained. Many large landfills are already collecting ambient air methane data based on existing regulations. The proposed method is based on the inverse solution of the standard Gaussian dispersion equations. However, only the VOC concentrations and locations are required. The locations of maximum likelihood of the point sources are predicted using Voronoi diagrams, and importance sampling is performed to further refine the locations. Point source strengths are calculated using non-negative least squares, and the point emission rates are then summed to give the total landfill emission rate. The proposed method is successfully demonstrated on a series of four landfill case studies. Three hypothetical landfills were selected for validation studies by forward and backward solution of the dispersion equations. The fourth case study is an active central Florida MSW landfill. The proposed method shows promise in accurately and robustly predicting landfill gas emissions, and requires only measured ambient VOC concentrations and locations.

Revealing source signatures in ambient BTEX concentrations

Management of ambient concentrations of Volatile Organic Compounds (VOCs) is essential for maintaining low ozone levels in urban areas where its formation is under a VOC-limited regime. The significant decrease in traffic-induced VOC emissions in many developed countries resulted in relatively comparable shares of traffic and non-traffic VOC emissions in urban airsheds. A key step for urban air quality management is allocating ambient VOC concentrations to their pertinent sources. This study presents an approach that can aid in identifying sources that contribute to observed BTEX concentrations in areas characterized by low BTEX concentrations, where traditional source apportionment techniques are not useful. Analysis of seasonal and diurnal variations of ambient BTEX concentrations from two monitoring stations located in distinct areas reveal the possibility to identify source categories. Specifically, the varying oxidation rates of airborne BTEX compounds are used to allocate contributions of traffic emissions and evaporative sources to observed BTEX concentrations.

Source Apportionment of Ambient Volatile Organic Compounds in Beijing

The ambient air quality standard for ozone is frequently exceeded in Beijing in summer and autumn. Source apportionments of volatile organic compounds (VOCs), which are precursors of ground-level ozone formation, can be helpful to the further study of tropospheric ozone formation. In this study, ambient concentrations of VOCs were continuously measured with a time resolution of 30 min in August 2005 in Beijing. By using positive matrix factorization (PMF), eight sources for the selected VOC species were extracted. Gasoline-related emissions (the combination of gasoline exhaust and gas vapor), petrochemicals, and liquefied petroleum gas (LPG) contributed 52, 20, and 11%, respectively, to total ambient VOCs. VOC emissions from natural gas (5%), painting (5%), diesel vehicles (3%), and biogenic emissions (2%) were also identified. The gasoline-related, petrochemical, and biogenic sources were estimated to be the major contributors to ozone formation potentials in Beijing.

Chemical characterization of volatile organic compounds near the World Trade Center: Ambient concentrations and source apportionment

Concentrations of 53 volatile organic compounds (VOCs) are reported from four locations near the World Trade Center (WTC) (New York, USA) complex for canister samples collected from September 2001 through January 2002. Across the four sampling sites, mean concentrations ranged from 94.5 to 219 μ g m - 3 for total VOCs. The highest mean concentrations for individual VOCs at any site were for ethane ( 18.7 μ g m - 3 ) , isopentane ( 17.1 μ g m - 3 ) , and m , p -xylenes ( 17.0 μ g m - 3 ) . VOC concentrations were generally highest for samples collected north and west of the WTC complex. Concentrations of total VOCs (and most individual VOCs) decreased from the period when fires were present at the WTC complex (before 19 December 2001) to the period after fires. The EPA Unmix Version 5.0 receptor model was used to assess the impact of WTC fires and recovery efforts on ambient VOC concentrations. Four factors were identified: burning of building debris, a mixed recovery/heating source, motor vehicle exhaust, and a mixed gasoline source.

In-situ measurement of reactive hydrocarbons at Hohenpeissenberg with comprehensive two-dimensional gas chromatography (GC×GC-FID): use in estimating HO and NO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;

Abstract. During a field campaign at the Meteorological Observatory Hohenpeissenberg (MOHp) in July 2004, volatile organic compounds (VOCs) were measured using comprehensive two-dimensional gas chromatography (GC×GC). Comparison to routinely made gas chromatography mass spectrometry (GC-MS) measurements showed good agreement for a variety of anthropogenic and biogenic ambient VOCs ranging in concentration from below the detection limit (0.1 pmol mol−1) to 180 pmol mol−1. Pronounced diurnal cycles were found for both the biogenic and anthropogenic compounds, driven for the most part by the daily rise and fall of the boundary layer over the station. For the reactive compounds (lifetimes &lt;2 days), a significant, non-zero dependency of the variability on lifetime was found, indicating that chemistry (as opposed to transport alone) was playing a role in determining the ambient VOC concentrations. The relationship was exploited using a single-variate analysis to derive a daytime mean value of HO (5.3±1.4×106molecules cm−3), which compares well to that measured at the site, 3.2±2.3×106molecules cm−3. The analysis was extended to the night time data to estimate concentrations for NO3 (1.47±0.2×108molecules cm−3), which is not measured at the site. The feasibility of this approach for environments dominated by emissions of short-lived VOCs to estimate ambient levels of radical species is discussed.

Source Proximity and Outdoor-Residential VOC Concentrations: Results from the RIOPA Study

Ambient volatile organic compound concentrations outside residences were measured in Elizabeth, New Jersey as part of the Relationship of Indoor, Outdoor, and Personal A:r (RIOPA) study to assess the influence of proximity of the residences to known ambient emissions sources. The closest distances between the outdoor samplers and emission sources were determined using Geographic Information Systems (GIS)techniques. Multiple regression models were developed for residential ambient concentrations of aromatic hydrocarbons (BTEX), methyl tert butyl ether (MTBE), and tetrachloroethylene (PCE). The natural log transformed ambient concentrations of BTEX were inversely associated with distances to major roadways with high traffic densities and gasoline stations, atmospheric stability, temperature, and wind speed. Ambient MTBE levels were associated with inverse distance to gas stations and interstate highways. Residential ambient PCE concentration was inversely associated with distance to dry cleaning facilities, atmospheric stability, temperature, wind speed, and relative humidity. The linear regression models that include proximity to emission sources and meteorological variables explained 16-45% of the overall variation of ambient residential VOC concentrations. Meteorological conditions, especially atmospheric stability and temperature, explained 60-90% of the total variation in the regression models. The residential ambient air concentrations were 1.5-4 times higher than the urban background levels outside homes very close (<50 m) to ambient emission sources where approximately 7% of the population live. However, the relative increase of risk for disease is small and variations in air concentration in the background urban atmosphere are greater than those from the proximity to roadways.

Source identification and apportionment of volatile organic compounds in Houston, TX

Hourly concentrations of ambient volatile organic compounds (VOCs) were analyzed between June and October 2003 at three sites, in order to further understand emissions of VOCs in the Houston area. Ambient concentrations of 54 VOCs from three monitoring sites in the heavily industrialized Houston Ship Channel were analyzed using positive matrix factorization (PMF). Hourly concentrations were divided into weekly data sets and analyzed to determine the most important source types that contribute to the measured VOC concentrations at these three sites. For each monitoring site, three or four sources were identified for each week as major contributors to ambient VOC concentrations using PMF. The sources isolated by the model are consistent with the chemical compositions of refinery, petrochemical and evaporative emissions, which are also the dominant inventoried sources of VOCs in Houston Ship Channel region. A night-time data analysis was also performed at two sites to investigate the effect of photochemical reactions on source attribution of VOCs.