Contribution of isoprene to formaldehyde and ozone formation based on its oxidation products measurement in Beijing,China

The atmospheric mixing ratios of methacrolein (MACR) and methyl vinyl ketone (MVK), the two specific products from isoprene oxidation in the atmosphere, were measured in Beijing from March to November, 2006. Distinct amounts of MACR and MVK were detected during vegetable growing seasons from April to October with ambient levels of 0.11–0.67 ppbv and 0.19–1.36 ppbv, respectively. The reacted isoprene and its ozone formation potentials (OFPs) in Beijing were evaluated in the range of 0.49–3.46 ppbv and 6.4–44.7 ppbv, respectively, from April to October. OFP of the reacted isoprene accounted for 10.6–23.6% of the total OFPs of VOCs (including carbonyls and isoprene) and 6.38–29.9% of the photo-chemically produced ozone. The maximum OFP of the original emitted isoprene prior to its photo-oxidation was calculated as 56.0 ppbv in August. The contribution from the reacted isoprene in Beijing to HCHO formation was also estimated to be in the range of 0.35–2.45 ppbv from April to October, which accounted for 4.6–11.5% of ambient HCHO.     

Source profiles of volatile organic compounds associated with solvent use in Beijing,China

Compositions of volatile organic compound (VOC) emissions from painting applications and printing processes were sampled and measured by gas chromatography–mass spectrometry/flame ionization detection (GC–MS/FID) in Beijing. Toluene and C8 aromatics were the most abundant species, accounting for 76% of the total VOCs emitted from paint applications. The major species in printing emissions included heavier alkanes and aromatics, such as n-nonane, n-decane, n-undecane, toluene, and m/p-xylene. Measurements of VOCs obtained from furniture paint emissions in 2003 and 2007 suggest a quick decline in benzene levels associated with formulation changes in furniture paints during these years. A comparison of VOC source profiles for painting and printing between Beijing and other parts of the world showed significant region-specific discrepancies, probably because of different market demands and environmental standards. We conducted the evaluation of the source reactivities for various VOC emission sources. The ozone formation potential (OFP) for unit mass of VOCs source emissions is the highest for paint applications. Substituting solvent-based paints by water-based in Beijing will lead to an OFP reduction of 152,000 tons per year, which is more than 1/4 of the OFPs for VOCs emissions from vehicle exhaust in the city.     

VOC concentration characteristics in Southern Taiwan

The field investigations were conducted at four air quality monitoring sites in Southern Taiwan during northeasterly prevailing monsoon to collect 160 data sets on volatile organic compounds (VOCs) to evaluate the ozone formation potential (OFP) of the air mass. The gas chromatograph and high performance liquid chromatography analyzed 58 VOCs and two aldehydes, respectively. Among the four sampling sites, the order of the five VOC classes based on the reactivity approach was different from the concentration-based method. Alkenes as well as aromatics provided a major contribution for the OFP. The relative ranking of the species at the four sites were quite dissimilar. Toluene was the most in abundance at each site. The most abundant species at the windward and leeward sites was different. The reactivity of the air mass at the leeward sites showed a similar pattern and had higher reactivity than the windward sites. Comparisons of the two ratios, xylene/benzene and toluene/benzene were used to assess the relative age of the air parcels and provide evidence of transport.     

A diagnostic comparison of measured and model-predicted speciated VOC concentrations

This study compares speciated model-predicted concentrations (i.e., mixing ratios) of volatile organic compounds (VOCs) with measurements from the Photochemical Assessment Monitoring Stations (PAMS) network at sites within the northeastern US during June–August of 2006. Measurements of total non-methane organic compounds (NMOC), ozone (O₃), oxides of nitrogen (NO_x) and reactive nitrogen species (NO_y) are used for supporting analysis. The measured VOC species were grouped into the surrogate classes used by the Carbon Bond IV (CB4) chemical mechanism. It was found that the model typically over-predicted all the CB4 VOC species, except isoprene, which might be linked to overestimated emissions. Even with over-predictions in the CB4 VOC species, model performance for daily maximum O₃ was typically within ±15%. Analysis at an urban site in NY, where both NMOC and NO_x data were available, suggested that the reasonable ozone performance may be possibly due to compensating overestimated NO_x concentrations, thus modulating the NMOC/NO_x ratio to be in similar ranges as that of observations.     

C1–C8 volatile organic compounds in the atmosphere of Hong Kong: Overview of atmospheric processing and source apportionment

We present measurements of C₁–C₈ volatile organic compounds (VOCs) at four sites ranging from urban to rural areas in Hong Kong from September 2002 to August 2003. A total of 248 ambient VOC samples were collected. As expected, the urban and sub-urban sites generally gave relatively high VOC levels. In contrast, the average VOC levels were the lowest in the rural area. In general, higher mixing ratios were observed during winter/spring and lower levels during summer/fall because of seasonal variations of meteorological conditions. A variation of the air mass composition from urban to rural sites was observed. High ratios of ethyne/CO (5.6 pptv/ppbv) and propane/ethane (0.50 pptv/pptv) at the rural site suggested that the air masses over the territory were relatively fresh as compared to other remote regions. The principal component analysis (PCA) with absolute principal component scores (APCS) technique was applied to the VOC data in order to identify and quantify pollution sources at different sites. These results indicated that vehicular emissions made a significant contribution to ambient non-methane VOCs (NMVOCs) levels in urban areas (65±36%) and in sub-urban areas (50±28% and 53±41%). Other sources such as petrol evaporation, industrial emissions and solvent usage also played important roles in the VOC emissions. At the rural site, almost half of the measured total NMVOCs were due to combustion sources (vehicular and/or biomass/biofuel burning). Petrol evaporation, solvent usage, industrial and biogenic emissions also contributed to the atmospheric NMVOCs. The source apportionment results revealed a strong impact of anthropogenic VOCs to the atmosphere of Hong Kong in both urban/sub-urban and rural areas.     

Pollution characteristics of ambient volatile organic compounds (VOCs) in the southeast coastal cities of China

With the rapid urbanization, the southeast coastal cities of China are facing increasing air pollution in the past decades. Large emissions of VOCs from vehicles and petrochemical factories have contributed greatly to the local air quality deterioration. Investigating the pollution characteristics of VOCs is of great significance to the environmental risk assessment and air quality improvement. Ambient VOC samples were collected simultaneously from nine coastal cities of southeast China using the Tedlar bags, and were subsequently preprocessed and analyzed using a cryogenic preconcentrator and a gas chromatography–mass spectrometry system, respectively. VOC compositions, spatial distributions, seasonal variations and ozone formation potentials (OPFs) were discussed. Results showed that methylene chloride, toluene, isopropyl alcohol and n-hexane were most abundant species, and oxygenated compounds, aromatics and halogenated hydrocarbons were most abundant chemical classes (62.5–95.6 % of TVOCs). Both industrial and vehicular exhausts might contribute greatly to the VOC emissions. The VOC levels in the southeast coastal cities of China were sufficiently high (e.g., 6.5 μg?m^?3 for benzene) to pose a health risk to local people. A more serious pollution state was found in the southern cities of the study region, while higher VOC levels were usually observed in winter. The B/T ratio (0.26?±?0.09) was lower than the typical ratio (ca. 0.6) for roadside samples, while the B/E (1.6–7.6) and T/E (7.2–26.8) ratios were higher than other cities around the world, which indicated a unique emission profile in the study region. Besides, analysis on ozone formation potentials (OFPs) indicated that toluene was the most important species in ozone production with the accountabilities for total OFPs of 22.6 to 59.6 %.     

Effects of reactive hydrocarbons on ozone formation in southern Taiwan

Ambient air samples were collected at 13 air quality monitoring stations in Kaohsiung city, Kaohsiung county, and Pingtung county (KKP) to investigate the composition and spatial distribution of C₂–C₁₀ non-methane hydrocarbons (NMHCs) in southern Taiwan. Ozone formation potentials (OFPs) of NMHCs were estimated using maximum incremental reactivity (MIR) and k_OH method (reactivity of NMHC with OH radical) to assess the relative effects of hydrocarbons on ozone formation. The measurements showed that mixing ratios of toluene, ethene, ethyne, ethane, isopantane and propane were the highest among all measured species at most of the sampling sites. Nevertheless, considering both the photochemical reactivities and mixing ratios of all the measured species, toluene, xylene, ethene and propene were calculated to have the highest OFPs and reactivities. The OFPs and reactivities assessed by the MIR and k_OH methods for the four compounds accounted for 54.5% and 39.3% of all the measured species. Larger benefit margin of ozone abatement may be obtained by reducing emissions of a group of key species with high OFPs.2,2-dimethylbutane (22DMC4) was used as an indicator of traffic emissions to distinguish traffic from non-traffic contributions of key species in Kaohsiung metropolitan area. It revealed that the contribution of non-traffic source was significant for toluene, whereas xylene was found to be primarily from the traffic source in Kaohsiung metropolitan area during the sampling periods.     

Isoprene and its degradation products as strong ozone precursors in Insubria,Northern Italy

Frequent smog episodes occur during spring, summer, and autumn in Insubria, Northern Italy. On a test site in this area the atmospheric concentration of the photo-oxidants ozone and peroxyacetyl nitrate has been monitored over a year (2000) together with ozone precursors listed in the European Union Air Quality Directive 2002/3/EC, such as nitrous oxides (NO_X) and volatile organic compounds (VOC) including hydrocarbons and carbonyls. The results of this study revealed a strong impact of biogenic isoprene on the air quality.In winter isoprene was detected at the ppt level and correlated with anthropogenic VOC. However, during the growing season isoprene exhibited a distinct diurnal variation with maximum concentrations late in the afternoon reaching up 70 ppbC attributed to strong emissions from the abundant vegetation of broad-leaf deciduous trees in this area. A new HPLC-MS method was developed for the determination of isoprene's primary atmospheric oxidation products methacrolein as its 2,4-dinitrophenylhydrazone and methyl vinyl ketone as an unusual double derivative with 2,4-dinitrophenylhydrazine. Methacrolein and methyl vinyl ketone followed the same diurnal and annual trends as isoprene. The average monthly concentration of isoprene and these products ranged from around 10 ppbC in June, July and September to 20 ppbC in August, which constitutes 15–30% of C₃–C₉ VOCs. The contribution from isoprene photo-oxidation to the ambient air formaldehyde concentrations was also found to be high during this period ranging from 30% to 60% in May, June, July and August.From the atmospheric VOC and NO_X concentrations the local photochemical ozone formation was estimated by the incremental reactivity approach. The calculations showed that in summer isoprene's contribution to the local ozone formation was as high as 50–75%.     

Daily, weekly, and seasonal time courses of VOC concentrations in a semi-urban area near Barcelona

In order to study the daily, weekly, and seasonal patterns and possible origins of air concentrations of volatile organic compounds (VOCs), measurements were taken on a minute-by-minute basis with a PTR-MS in the vicinity of a highway in a semi-urban site near Barcelona. Four periods of the year were chosen and samples were taken under different meteorological conditions and at different phenological stages of the surrounding vegetation. None of the measured VOCs concentrations exceeded air-quality guidelines. The results showed that diurnal, weekly, and seasonal fluctuations in measured VOC concentrations depended on variations in the strength of sources, as well as on photochemical activity and meteorological conditions. There was a decrease in concentrations in most VOCs when mixing depth, photochemical destruction, and wind speed increased at midday. On the other hand, high values of some VOCs occurred at night when the strength of their sinks and the mixing layer decreased. Interestingly, in June, night emissions and concentration peaks of methanol and acetone occurred in periods with dew formation and no wind. VOCs related to anthropogenic emissions presented a weekly pattern of variation with a clear distinction being found between working days and the weekend. The seasonal variation showed higher levels in December for all VOCs, except for isoprene. The thinning of the mixing layer leading to greater concentrations of volatiles and lower wind speeds in winter could account for those higher VOC levels. Benzene and toluene originated mainly from anthropogenic emissions. The sources of acetaldehyde, methanol, and acetone appeared to be mainly biogenic and these compounds were the most abundant of all the measured VOCs. Isoprene concentration patterns suggest a predominantly anthropogenic origin in December and March and a mainly biogenic origin in June and October. All these data provide useful information on the dynamics of VOCs in an area where ozone levels in summer exceed quite often the standard protection thresholds for O₃.     

Application of OMI observations to a space-based indicator of NOx and VOC controls on surface ozone formation

We investigated variations in the relative sensitivity of surface ozone formation in summer to precursor species concentrations of volatile organic compounds (VOCs) and nitrogen oxides (NO_x) as inferred from the ratio of the tropospheric columns of formaldehyde to nitrogen dioxide (the “Ratio”) from the Aura Ozone Monitoring Instrument (OMI). Our modeling study suggests that ozone formation decreases with reductions in VOCs at Ratios <1 and NO_x at Ratios >2; both NO_x and VOC reductions may decrease ozone formation for Ratios between 1 and 2. Using this criteria, the OMI data indicate that ozone formation became: 1. more sensitive to NO_x over most of the United States from 2005 to 2007 because of the substantial decrease in NO_x emissions, primarily from stationary sources, and the concomitant decrease in the tropospheric column of NO₂, and 2. more sensitive to NO_x with increasing temperature, in part because emissions of highly reactive, biogenic isoprene increase with temperature, thus increasing the total VOC reactivity. In cities with relatively low isoprene emissions (e.g., Chicago), the data clearly indicate that ozone formation became more sensitive to NO_x from 2005 to 2007. In cities with relatively high isoprene emissions (e.g., Atlanta), we found that the increase in the Ratio due to decreasing NO_x emissions was not obvious as this signal was convolved with variations in the Ratio associated with the temperature dependence of isoprene emissions and, consequently, the formaldehyde concentration.     

Differences between Weekday and Weekend Air Pollutant Levels in Atlanta; Baltimore; Chicago; Dallas–Fort Worth; Denver; Houston; New York; Phoenix; Washington,DC; and Surrounding Areas

Abstract

We evaluated day-of-week differences in mean concentrations of ozone (O₃) precursors (nitric oxide [NO], nitrogen oxides [NO_x], carbon moNO_xide [CO], and volatile organic compounds [VOCs]) at monitoring sites in 23 states comprising seven geographic focus areas over the period 1998– 2003. Data for VOC measurements were available for six metropolitan areas in five regions. We used Wednesdays to represent weekdays and Sundays to represent weekends; we also analyzed Saturdays. At many sites, NO, NO_x, and CO mean concentrations decreased at all individual hours from 6:00 a.m. to 3:00 p.m. on Sundays compared with corresponding Wednesday means. Statistically significant (p < 0.01) weekend decreases in ambient concentrations were observed for 92% of NO_x sites, 89% of CO sites, and 23% of VOC sites. Nine-hour (6:00 a.m. to 3:00 p.m.) mean concentrations of NO, NO_x, CO, and VOCs declined by 65, 49, 28, and 19%, respectively, from Wednesdays to Sundays (median site responses). Despite the large reductions in ambient NO_x and moderate reductions in ambient CO and VOC concentrations on weekends, ozone and particulate matter (PM) nitrate did not exhibit large changes from week-days to weekends. The median differences between Wednesday and Sunday mean ozone concentrations at all monitoring sites ranged from 3% higher on Sundays for peak 8-hr concentrations determined from all monitoring days to 3.8% lower on Sundays for peak 1-hr concentrations on extreme-ozone days. Eighty-three percent of the sites did not show statistically significant differences between Wednesday and weekend mean concentrations of peak ozone. Statistically significant weekend ozone decreases occurred at 6% of the sites and significant increases occurred at 11% of the sites. Average PM nitrate concentrations were 2.6% lower on Sundays than on Wednesdays. Statistically significant Sunday PM nitrate decreases occurred at one site and significant increases occurred at seven sites.     

Global comparison of VOC and CO observations in urban areas

Speciated volatile organic compound (VOC) and carbon monoxide (CO) measurements from the Marylebone Road site in central London from 1998 through 2008 are presented. Long-term trends show statistically significant decreases for all the VOCs considered, ranging from ?3% to ?26% per year. Carbon monoxide decreased by ?12% per year over the measurement period. The VOC trends observed at the kerbside site in London showed greater rates of decline relative to trends from monitoring sites in rural England (Harwell) and a remote high-altitude site (Hohenpeissenberg), which showed decreases for individual VOCs from ?2% to ?13% per year. Over the same 1998 through 2008 period VOC to CO ratios for London remained steady, an indication that emissions reduction measures affected the measured compounds equally. Relative trends comparing VOC to CO ratios between Marylebone Road and Hohenpeissenberg showed greater similarities than absolute trends, indicating that emissions reductions measures in urban areas are reflected by regional background locations. A comparison of VOC mixing ratios and VOC to CO ratios was undertaken for London and other global cities. Carbon monoxide and VOCs (alkanes greater than C₅, alkenes, and aromatics) were found to be strongly correlated (>0.8) in the Annex I countries, whereas only ethene and ethyne were strongly correlated with CO in the non-Annex I countries. The correlation results indicate significant emissions from traffic-related sources in Annex I countries, and a much larger influence of other sources, such as industry and LPG-related sources in non-Annex I countries. Yearly benzene to ethyne ratios for London from 2000 to 2008 ranged from 0.17 to 0.29 and compared well with previous results from US cities and three global megacities.     

Characteristics and diurnal variations of NMHCs at urban,suburban, and rural sites in the Pearl River Delta and a remote site in South China

The Pearl River Delta (PRD) is one of the most industrialized and urbanized regions in China. With rapid growth of the economy, it is suffering from deteriorating air quality. Non-methane hydrocarbons (NMHCs) were investigated at urban and suburban sites in Guangzhou (GZ), a rural site in PRD and a clean remote site in South China, in April 2005. Additional roadside samples in GZ and Qingxi (QX, a small industrial town in PRD), ambient air samples at the rooftop of a printing factory in QX and exhaust samples from liquefied petroleum gas (LPG)—fueled taxis in GZ were collected to help identify the source signatures of NMHCs. A large fraction of propane (47%) was found in exhaust samples from LPG-fueled taxis in GZ and extremely high levels of toluene (2.0–3.1 ppmv) were found at the rooftop of the printing factory in QX. Vehicular and industrial emissions were the main sources of NMHCs. The effect of vehicular emission on the ambient air varied among the three PRD sites. The impact of industrial emissions was widespread and they contributed greatly to the high levels of aromatic hydrocarbons, especially toluene, at the three PRD sites investigated. Leakage from vehicles fueled by LPG contributed mainly to the high levels of propane and n-butane at the urban GZ site. Ethane and ethyne from long-range transport and isoprene from local biogenic emission were the main contributors to the total hydrocarbons at the remote site. Diurnal variations of NMHCs showed that the contribution from vehicular emissions varied with traffic conditions and were more influenced by fresh emissions at the urban site and by aged air at the suburban and rural sites. Isoprene from biogenic emission contributed largely to the ozone formation potential (OFP) at the remote site. Ethene, toluene and m/p-xylene were the main contributors to the OFP at the three PRD sites.     

Source profiles and ozone formation potentials of volatile organic compounds in three traffic tunnels in Kaohsiung,Taiwan

Twenty-five volatile organic compounds (VOCs) up to C10 were measured using Carbotrap multibed thermal adsorption tubes during the morning and afternoon rush hours on four different days in all three traffic tunnels in Kaohsiung, Taiwan. A gas chromatograph (GC) equipped with a flame-ionization detector (FID) was then used to analyze the VOCs. The analytical results show that VOC concentrations increase with traffic flow rate, and emission profiles in the three tunnels are mostly in the range C2-C6. In addition to the traffic conditions and vehicle type, the pattern of emissions in each tunnel was also influenced by other factors, such as vehicle age, nearby pollution sources, and the spatial or temporal variation of VOCs in the urban atmosphere. The ozone formation potential (OFP) in each tunnel was assessed based on the maximum incremental reactivities of the organic species, demonstrating that OFP increases with traffic flow rate. Vehicle distribution influences the contributions of organic group to OFP in a tunnel. Meanwhile, when ranked in descending order of contribution to OFP in all tunnels, the organic groups followed the sequence olefins, aromatics, and paraffins.     

Weekday/Weekend differences in ambient air pollutant concentrations in atlanta and the southeastern United States

The authors quantified changes between mean weekday and weekend ambient concentrations of ozone (O3) precursors (volatile organic compounds [VOC], carbon monoxide [CO], nitric oxide, and oxides of nitrogen [NOx]) in Atlanta and surrounding areas to observe how weekend precursor emission levels influenced ambient O3 levels. The authors analyzed CO, nitric oxide (NO), and NO, measurements from 1998 to 2002 and speciated VOC from 1996 to 2003. They observed a strong weekend effect in the Atlanta region, with median daytime (6:00 a.m. to 3:00 p.m. Eastern Standard Time) decreases of 62%, 57%, and 31%, respectively, in the ambient levels of NO, NOx, and CO from Wednesdays to Sundays, during the ozone season (March to October). They also observed significant decreases in ambient VOC levels between Wednesdays and Sundays, with decreases of 28% for the sum of aromatic compounds and 19% for the sum of Photochemical Assessment Monitoring Stations target compounds. Despite large reductions in O3 precursor levels on weekends, day-of-week differences in O3 mixing ratios in and near Atlanta were much smaller. Averaging overall O3-season days, the 1-hr and 8-hr mean peak daily O3 maxima on Sundays were 4.5% and 2.3% lower, respectively, than their mean levels on Wednesdays (median of 14 site differences), with no sites showing statistically significant Wednesday-to-Sunday differences. When restricted to high-O3 days (highest 3 peak O3 days per day of week per site per year), the 1-hr and 8-hr Sunday O3 mixing ratios were 11% and 10% lower, respectively, than their mean peak levels on Wednesdays (median of 14 site differences), with 6 of 14 sites showing statistically significant Wednesday-to-Sunday differences. The analyses of weekday/weekend differences in O3 precursor concentrations show that different emission reductions than normally take place each weekend will be required to achieve major reductions in ambient ozone levels in the Atlanta area.     

Characteristics and source apportionment of VOCs measured in Shanghai,China

Volatile organic compounds (VOCs) were measured from 2007 to 2010 at the center of Shanghai, China. Because VOCs are important precursors for ozone photochemical formation, detailed information of VOC sources needs to be investigated. The results show that the measured VOC concentrations in Shanghai are dominated by alkanes (43%) and aromatics (30%), following by halo-hydrocarbons (14%) and alkenes (6%). Based on the measured VOC concentrations, a receptor model (PMF; positive matrix factorization) coupled with the information related to VOC sources (the distribution of major industrial complex, meteorological conditions, etc.) is applied to identify the major VOC sources in Shanghai. The result shows that seven major VOC sources are identified by the PMF method, including (1) vehicle related source which contributes to 25% of the measured VOC concentrations, (2) solvent based industrial source to 17%, (3) fuel evaporation to 15%, (4) paint solvent usage to 15%, (5) steel related industrial production to 12%, (6) biomass/biofuel burning to 9%, and (7) coal burning to 7%. Furthermore, ozone formation potential related to VOC sources is calculated by the MIR (maximum incremental reactivity) technique. The most significant VOC source for ozone formation potential is solvent based industrial sources (27%), paint solvent usage (24%), vehicle related emissions (17%), steel related industrial productions (14%), fuel evaporations (9%), coal burning (6%), and biomass/biofuel burning (3%). The weekend effect on the VOC concentrations shows that VOC concentrations are generally higher in the weekdays than in the weekends at the sampling site, suggesting that traffic conditions and human activities have important impacts on the VOC emissions in Shanghai.     

Interlaboratory Study of a Test Method Measuring Total Volatile Organic Compound Content of Consumer Products

Abstract

Consumer products are potentially significant sources of volatile organic compounds (VOCs), which are precursors to the formation of ozone in photochemical smog. To address the problem of ozone formation in ambient air, the U.S. Environmental Protection Agency (EPA) has been involved in the development of test methods for measuring the VOC content of consumer products. This paper describes results of an interlaboratory study to estimate the repeatability (precision of analyses performed by a single laboratory) and reproducibility (precision of analyses performed by different laboratories) of the consumer products’ VOC measurement method based on EPA Method 24 (for VOCs in surface coatings).

The mean method repeatability was 2.7 wt % VOC, and the mean method reproducibility was 4.8 wt % VOC. Method repeatability ranged from 0.2 to 4.4 wt % VOC, and reproducibility ranged from 0.6 to 11.9 weight percent VOC. The precision of the VOC method for consumer

products is similar to the precision of EPA Method 24 for surface coatings.     

NMOC,ozone, and organic aerosol in the southeastern United States, 1999–2007: 1. Spatial and temporal variations of NMOC concentrations and composition in Atlanta,Georgia

Volatile organic compounds (VOCs) are emitted from anthropogenic and natural (biogenic) sources into the atmosphere. Characterizing their ambient mixing ratios or concentrations is a challenge because VOCs comprise hundreds of species, and accurate measurements are difficult. Long-term hourly and daily-resolution data have been collected in the metropolitan area of Atlanta, Georgia, a major city dominated by motor vehicle emissions. A series of observations of daily, speciated C₂–C₁₀ non-methane organic compounds (NMOC) and oxygenated hydrocarbons (OVOC) in mid-town Atlanta (Jefferson Street, JST) are compared with data from three urban-suburban sites and a nearby non-urban site. Annual-average mixing ratios of NMOC and OVOC at JST declined from 1999 through 2007. Downward trends in NMOC, CO, and NO_y corroborate expected emission changes as reflected in emission inventories for Atlanta’s Fulton County. Comparison of the JST NMOC composition with data from roadside and tunnel sampling reveals similarities to motor vehicle dominated samples. The JST annual average VOC-OH reactivities from 1999 to 2007 were relatively constant compared with the decline in annual-average NMOC mixing ratios. Mean reactivity at JST, in terms of concentration*k_OH, was approximately 40% alkenes, 22% aromatics, 16% isoprene and 6% other biogenics, 13% C₇–C₁₀ alkanes and 3% C₂-C₆ alkanes, indicating that biogenic NMOCs are important but not dominant contributors to the urban reactive NMOC mix. In contrast, isoprene constituted ～50% of the VOC-OH reactivities at two non-urban sites. Ratios of 24-hour average CO/benzene, CO/isopentane, and CO/acetylene concentrations indicate that such species are relatively conserved, consistent with their low reactivity. Ratios of more-reactive to less-reactive species show diurnal variability largely consistent with expected emission patterns, transport and mixing of air, and chemical processing.     

A theoretical investigation of the pressure and temperature dependence of atmospheric ozone deposition to trees

Methods for describing the exposure patterns of forests to atmospheric ozone concentrations are compared with special emphasis on the situation at high altitudes, such as the Appalachian Mountains of the eastern USA. Limitations to the use of ozone concentration as mass per unit volume are discussed and a correction for temperature and pressure changes is derived. If identical ozone mass concentrations were measured at two sites separated by 2000 m elevation, the ozone flux at the lower site would exceed the flux at the higher site by 4-8% due to temperature and pressure effects on both air volume and ozone deposition velocity. It is recommended that ozone exposures be described in terms of 'flux-corrected' mass concentrations or volumetric mixing ratios when ambient ozone data from sites at different altitudes are to be compared.