Total Non-methane Hydrocarbons Research Articles

Variations and sources of ambient formaldehyde for the 2008 Beijing Olympic games

As the host city of the 2008 Olympic games, Beijing implemented a series of air pollution control measures before and during the Olympic games. Ambient formaldehyde (HCHO) concentrations were measured using a fluorometric instrument based on a diffusion scrubber and the Hantzsch reaction; hydrocarbons were simultaneously measured using gas chromatography–mass spectrometry (GC–MS). Meteorological parameters, CO, O 3, and NO 2 concentrations were measured by standard commercial instrumentation. In four separate periods: (a) before the vehicle plate number control (3–19 July); (b) during the Olympic Games (8–24 August); (c) during the Paralympic Games (6–17 September) and (d) after the vehicle control was ceased (21–28 September), the average HCHO mixing ratios were 7.31 ± 2.67 ppbv, 5.54 ± 2.41 ppbv, 8.72 ± 2.48 ppbv, and 6.42 ± 2.79 ppbv, while the total non-methane hydrocarbons (NMHCs) measured were 30.41 ± 18.08 ppbv, 18.12 ± 9.38 ppbv, 30.50 ± 13.37 ppbv, and 33.33 ± 15.85 ppbv, respectively. Both HCHO and NMHC levels were the lowest during the Olympic games, and increased again during the Paralympic games even with the same vehicle control measures operative. Similar diurnal HCHO and O 3 patterns indicated that photo-oxidation of NMHCs may be the major source of HCHO. The diurnal profile of total NMHCs was very similar to that of NO 2 and CO: morning and evening peaks appeared in rush hours, indicating even after strict vehicle control, automobile emission may still be the dominant source of the HCHO precursors. The contributions of HCHO, alkanes, alkenes, and aromatics to OH loss rates were also calculated. HCHO contributed 22 ± 3% to the total VOCs and 24 ± 1% to the total OH loss rate. HCHO was not only important in term of abundance, but also important in chemical reactivity in the air.

Effectiveness of a Florida Landfill Biocover for Reduction of CH4 and NMHC Emissions

Methane-oxidizing "biocovers" were constructed at the Leon County Landfill (Florida). The primary goal was to determine if a biocover placed above the existing thin (15 cm) intermediate clay cover would be capable of mitigating CH(4) and nonmethane hydrocarbon (NMHC) emissions to the atmosphere in this subtropical environment. A secondary goal was to maximize the use of locally recycled materials for biocover construction. The biocovers consisted of 30 or 60 cm of ground garden waste placed over a 15 cm gas distribution layer (clean crushed recycled glass from discarded fluorescent lights). The deep biocover reduced methane fluxes relative to the controls during temporal monitoring over more than a year; in large part, these reductions were attributable to increased methane oxidation. Both the shallow and the deep biocover exhibited significant percentages of negative fluxes (uptake of atmospheric methane) relative to the nonbiocover controls which had consistently positive fluxes. The overall annual effectiveness/performance of the biocover was limited by seasonally high moisture contents and the thin gas distribution layer. For NMHCs, the deep biocover demonstrated substantial reductions for nonmethane hydrocarbon emissions with high percentages of negative fluxes for several hydrocarbon groups, especially the aromatics, alkanes, and lower chlorinated compounds. Ranges of measured NMHC emissions (10(-9) to 10(-3) g m(-2) d(-1)) were similar to previous studies in the literature. Conservative calculations based on field data for total NMHC emissions from the 60 cm biocover area indicate that current U.S. Environmental Protection Agency (EPA) regulatory methods overestimate emissions by more than 2 orders of magnitude, suggesting that improved field-validated methods are needed.

Characteristics of ambient C 2–C 11 non-methane hydrocarbons in metropolitan Nagoya, Japan

To understand the characteristics of non-methane hydrocarbon (NMHC) abundance in an urban air of Nagoya, one of the metropolitan areas of Japan, 48 species of C 2–C 11 NMHCs were measured with a measurement system, developed in this study, by using gas chromatography with flame ionization detection (GC/FID) continuously for one year from December 2003 to November 2004. Annual mean concentration of NMHCs in normal and propylene equivalent (PE) in Nagoya was compared with those in four urban areas of Seoul, London, Lille, and Dallas to extract characteristics of urban air. While the absolute values of the normal and PE concentrations of alkanes, alkenes, alkyne, and aromatics were significantly different among these urban areas, the proportions of each chemical group to the total NMHC were not so different. In Nagoya, the total normal concentration was high from November to February and low from June to August. The pattern of the seasonal variation was influenced mainly by that of alkanes. On the other hand, the total PE concentration was high from July to December and low from January to June. The pattern of the seasonal variation was influenced mainly by those of alkenes and aromatics. Particularly the normal concentration of isoprene was high from May to September because of large emission associated with activity of plants. As the results, in summer, the PE concentration of isoprene was especially high, and its contribution to the total NMHCs measured in this study was approximately 40%. The total PE concentrations were high in summer when the concentration of OH radicals is also high, suggesting that the productions of ozone and secondary organic aerosol (SOA) are likely to be promoted in summer of Nagoya.

Emissions from grassland burning in Kaziranga National Park, India – analysis from IRS-P6 AWiFS satellite remote sensing datasets

Biomass burning from vegetation fires is an important source of greenhouse gas emissions. In this study, we quantify biomass burning emissions from grasslands from the highly sensitive Kaziranga National Park, Assam, Northeast India. Most of the fires in the park are ‘controlled burning fires’ set by the park officials for management purposes. We evaluated the short-term impacts of fires and the resulting air pollution through integrating biomass burnt information from satellite remote sensing datasets. IRS-P6 Advanced Wide Field Sensor (AWiFS) data during March and April corresponding to dry season were evaluated to delineate the burnt areas. These burnt area estimates were then integrated with biomass data and emission factors for quantifying the greenhouse gas emissions. Results suggested that of the total study area of 37,822 ha, nearly 3163.282 ha has been burnt during March, 2005. Within one month, the burnt area increased to 7443.92 ha by April, i.e., from 8.36% to 19.68%. In total, biomass burning from the grasslands contributed to 29.65 Tg CO2, 1.19 Tg CO, 0.071 Tg NOx, 0.042 Tg CH4, 0.0625 Tg total non-methane hydrocarbons, 0.152 Tg of particulate matter, and 0.062 Tg of organic carbon and 0.008 Tg of black carbon during April. The importance of ‘fire’ as a management tool for maintaining the wildlife habitat has been highlighted in addition to some of the adverse affects of air pollution resulting from such management practices. The results from this study will be useful to forest officials as well as policy makers to undertake some sustainable forest management practices to maintain an ideal habitat for Kaziranga's wildlife.

Carbonyls and non-methane hydrocarbons at a rural mountain site in northeastern United States

Measurements of carbonyls and C2–C6 non-methane hydrocarbons (NMHCs) were made in ambient air at a rural site at the summit of Whiteface Mountain (WFM) in New York State. Alkanes dominated in the samples, with ethane and propane making up about 55% of the total on a carbon-atom basis. Ethane, the longest-lived of the NMHCs, showed a mixing ratio in the range of 0.86–2.1ppbv. Photochemical ageing analysis indicated an anthropogenic influence on the NMHC levels. The photochemical reactivity of the hydrocarbons, calculated in terms of propylene-equivalent concentration, was dominated by alkenes (propene and ethene), which accounted for 74% of the total NMHC sum. Air mass back-trajectories have been used to investigate the origin of the observed NMHCs and carbonyls. Higher concentrations were found when air masses arrived from the midwestern US corridor. Acetone was the most abundant species, comprising from 31% to 53% of the total detected carbonyls, followed by MEK (15–53%), HCHO (7–39%), and CH3CHO (7–19%). Average concentrations were determined to be 1.61ppbv for CH3C(O)CH3, 1.40ppbv for MEK, 1.16ppbv for HCHO, and 0.49ppbv for CH3CHO. The variations in carbonyl concentrations were observed to follow patterns similar to variations in O3 concentrations, typical of secondary products. Correlations and statistical analysis of the carbonyls and NMHCs were performed, and showed that most of the compounds derived from mixing and photochemical transformation of long-range transported pollutants from the major source areas. Ranking of the carbonyls with respect to removal of the OH radical showed HCHO to be the most important species, followed by CH3CHO, MEK, and CH3C(O)CH3.

Characterization of ozone precursors in the Pearl River Delta by time series observation of non-methane hydrocarbons

Continuous hourly observation of more than 50 non-methane hydrocarbons (NMHCs) from C 3 to C 12 was performed between 16 October and 5 November 2004 in the Pearl River Delta (PRD) area by two automated gas chromatographs deployed separately at an urban site in downtown Guangzhou and a rural site in Xinken. Distinct differences in diurnal patterns of NMHCs are found between the two sites. In Guangzhou, peak concentrations were usually seen after dusk at the traffic rush hour, whereas the maxima in Xinken occurred between late night and early morning. High correlation between NO x , CO, and volatile organic compounds (VOCs) in Guangzhou suggests that motor vehicle exhaust is the dominant source of NMHCs in Guangzhou. It is also found that propane, iso-butane, and n-butane accounted for nearly 40% of the total NMHC concentration in Guangzhou, possibly due to the wide use of liquefied petroleum gas (LPG) as motor vehicle fuel in Guangzhou. Principal component analysis (PCA) of Xinken's dataset reveals that reactive alkenes are more depleted than alkanes and aromatics, providing evidence that the air masses arriving at Xinken are more aged in terms of photochemistry compared to the source area of Guangzhou. Using the ratio of ethylbenzene to m, p-xylenes as an effective age indicator, it is also found that the air in Xinken is substantially more aged than that in Guangzhou, consistent with the relatively smaller percentage of alkenes found in Xinken than in Guangzhou. Furthermore, the daily peak of the age indicator occurs in the afternoon between 2 and 5 p.m., concurrent in time with the ozone peak. The peak values of this indicator of Xinken are generally higher than those of Guangzhou by about a factor of 3, consistent with the much higher ozone levels found in Xinken.

Effect of Liquefied Petroleum Gas on Ozone Formation in Guadalajara and Mexico City

Leakages of liquefied petroleum gas (LPG) are suspected to contribute greatly to ozone (O3) formation in Mexico City. We tested such a hypothesis by outdoor captive-air irradiation (CAI) experiments in the two largest Mexican metropolitan areas: Guadalajara (GMA) in 1997 and Mexico City (MCMA) in 2000. O3 was monitored in each city for 20 days (8:00 a.m.–6:00 p.m.) in smog chambers containing unaltered morning air or morning air enriched with either commercial LPG or LPG synthetic mixture 60/40 (propane and butane). Tested additions of both components were 35% (by volume) in GMA and 60% (by volume) in MCMA. The addition effects on O3 (max) were compared with effects from diluting LPG components or total nonmethane hydrocarbons (tNMHCs) by 50%. Diluting tNMHCs had the greatest absolute effect at both cities: it lowered O3 (max) by 24% in GMA and 55% in MCMA. Adding commercial LPG increased O3 (max) by 6% in GMA and 28% in MCMA; whereas adding LPG synthetic mixture 60/40 caused a similar increase in O3 (max), 4 and 21% in GMA and MCMA, respectively. Compared with dilution of tNMHCs, dilution of LPG-associated compounds had a smaller decreasing effect on O3 (max), only 4% in GMA and 15% in MCMA. These results show that commercial LPG and LPG synthetic mixture 60/40 affect O3 formation to a lesser extent than estimated previously.

Hydrocarbon observations and ozone production rates in Western Houston during the Texas 2000 Air Quality Study

Measurements of total non-methane hydrocarbon in whole air canisters collected from the top of a skyscraper on the western edge of Houston, Texas are summarized with an emphasis on samples collected during the passage of plumes of O3 and the associated rapid increase in the mixing ratio of this species. The back-trajectories associated with these events showed a pronounced deceleration of air parcels over central and western Houston and were not necessarily associated with direct passage over the petrochemical plants located in the heavily industrialized eastern part of Houston. As a result of the time these air parcels spent over the central and western parts of Houston, their VOC mix and associated chemical production rates were expected to differ from similar observations made over eastern Houston from aircraft sampling at low altitudes. Although periods of high O3 in the western part of the city were closely associated with light alkenes, these same observations show isoprene to make a significant contribution to the total VOC reactivity in the early afternoon (the start of peak photochemical activity) in contrast to observations made east of our sampling site that found the reactivity to be dominated by anthropogenic species. By initializing a 0-dimensional chemical kinetic model with observations made at the Williams Tower, we find that the ozone production efficiency scaled linearly to the ratio of total hydrocarbons and NOx, with an average OPE of 7.2, ranging from 2.3 to 16.9; these values are smaller than those reported in eastern Houston, suggesting a strong gradient in photochemical productivity across the city.

Modeling ozone photochemistry and evaluation of hydrocarbon emissions in the Mexico City metropolitan area

Emissions of volatile organic compounds (VOCs) and of CO are often underestimated, and correcting this underestimate is important for modeling ozone formation and sensitivity. The California Institute of Technology three‐dimensional photochemical model is used to test the official emissions inventory for the Mexico City metropolitan area through a direct comparison of measured and modeled total nonmethane hydrocarbons (NMHCs) and CO. The model is applied to six 2‐day periods during the IMADA measurement campaign of March 1997. When using emissions based on the official emissions inventory, the model significantly underestimates measurements of total NMHCs and of CO. A best fit to the measurements (with lowest bias) is found when increasing emissions of CO and VOCs by factors of 2 and 3, respectively. Adjusting total emissions accordingly, the model produces good estimates of ozone and NOx, with average normalized biases over 6 days of 3% and 32%, respectively, and with better agreement during daytime hours. This agreement for ozone and NOx supports the suggestion that VOC and CO emissions are underestimated. Other uncertainties are analyzed, finding that while some uncertainties are important, none is individually significant enough to account for the discrepancy. Correcting the total emissions, the overall model performance is found to be adequate, particularly on 3 days, for the model to be used for analysis of control strategies. Using the results of a chemical mass balance identification of NMHC sources highlights sources that are more likely underestimated, but confidence in the appropriate correction to emissions from different sources is low and should be investigated further.

C 3–C 12 non-methane hydrocarbons in subtropical Hong Kong: spatial–temporal variations, source–receptor relationships and photochemical reactivity

Annual data on C 3–C 12 non-methane hydrocarbons (NMHCs) from different areas in Hong Kong are analyzed to examine the spatial distribution, seasonal variation, source–receptor relationships, and photochemical reactivity of NMHCs in subtropical Hong Kong. As expected, the highest levels of NMHCs were found at roadsides, and the lowest levels were observed at a rural site. For seasonal variations, the rural site showed the lowest NMHCs levels in summer, but the roadside site gave a different picture, with the highest NMHCs levels in summer. This was believed to be due to the strong evaporation of alkanes in the hot season. With the exception of isoprene, NMHCs levels in Hong Kong were generally low compared to those of other overseas cities. Principal component analysis suggested that while the isoprene at the rural site mainly came from biogenic emissions, vehicular emissions were the major source in the urban areas, especially at roadsides. Ratios of hydrocarbons with different reactivities were also analyzed to evaluate the ages of air masses and emission ratios. A high toluene-to-benzene ratio at roadsides was due to the widespread use of aromatic-rich unleaded fuels in Hong Kong. The ratios of total NMHCs to nitrogen oxides were found to be 2 to 10 (ppbC/ppbv) indicating that the formation of photochemical ozone (O 3) in Hong Kong is controlled by the levels of NMHCs. The reactivity of hydroxyl radicals (OH) and O 3 formation potential of NMHCs were evaluated using the propene-equivalent concentration and maximum incremental reactivity. Isoprene was found to have the highest OH-reactivity and O 3 formation potential at the rural site, while toluene was the most important contributor to the two parameters at the roadside site. These results are valuable for the understanding of O 3 pollution in Hong Kong and the formulation of an effective strategy to manage O 3.

Source apportionment of ambient non-methane hydrocarbons in Hong Kong: Application of a principal component analysis/absolute principal component scores (PCA/APCS) receptor model

Receptor-oriented source apportionment models are often used to identify sources of ambient air pollutants and to estimate source contributions to air pollutant concentrations. In this study, a PCA/APCS model was applied to the data on non-methane hydrocarbons (NMHCs) measured from January to December 2001 at two sampling sites: Tsuen Wan (TW) and Central & Western (CW) Toxic Air Pollutants Monitoring Stations in Hong Kong. This multivariate method enables the identification of major air pollution sources along with the quantitative apportionment of each source to pollutant species. The PCA analysis identified four major pollution sources at TW site and five major sources at CW site. The extracted pollution sources included vehicular internal engine combustion with unburned fuel emissions, use of solvent particularly paints, liquefied petroleum gas (LPG) or natural gas leakage, and industrial, commercial and domestic sources such as solvents, decoration, fuel combustion, chemical factories and power plants. The results of APCS receptor model indicated that 39% and 48% of the total NMHCs mass concentrations measured at CW and TW were originated from vehicle emissions, respectively. 32% and 36.4% of the total NMHCs were emitted from the use of solvent and 11% and 19.4% were apportioned to the LPG or natural gas leakage, respectively. 5.2% and 9% of the total NMHCs mass concentrations were attributed to other industrial, commercial and domestic sources, respectively. It was also found that vehicle emissions and LPG or natural gas leakage were the main sources of C 3–C 5 alkanes and C 3–C 5 alkenes while aromatics were predominantly released from paints. Comparison of source contributions to ambient NMHCs at the two sites indicated that the contribution of LPG or natural gas at CW site was almost twice that at TW site. High correlation coefficients (R 2 > 0.8) between the measured and predicted values suggested that the PCA/APCS model was applicable for estimation of sources of NMHCs in ambient air.

Liquefied petroleum gas effect on ozone formation in Mexico city

An experimental study of outdoor smog chambers was carried out to determine effects of liquefied petroleum gas (LPG) on maximum ozone (O 3 max). 60% additions of commercial LPG and 60%-propane/40% butane mixture of the initial concentration were introduced into eight smog chambers containing morning ambient air of Mexico City metropolitan area (MCMA). The ozone concentrations in each chamber were monitored throughout the day to determine the maximum of ozone. Dilution experiments of 50% total hydrocarbons and associated compounds to LPG in morning ambient air were carried out too. The results showed, that by increasing 60% of the associated compounds to LPG in the air of MCMA or diminishing 50% of them, had not an appreciable influence. The largest effect on ozone formation is determined by total nonmethane hydrocarbon (tNMHC) contained in the atmosphere, being the maximum of ozone formed in the smog chambers, on the average it diminished a 55%. C 3 and C 4 compounds associated to LPG only contribute a 14% of the total ozone formation.

Measurement of Traffic Related Toxic Air Pollutants in an Urban Atmosphere

Nose-level measurements of air toxics were made along a busy urban street in Ottawa, Canada for 2 hr periods during morning, noon, and afternoon rush hours in the winter and summer of 2000. Measurements were also made in a commuter car and a transit bus during morning and afternoon commutes in 2000. The main objectives of the study were to establish a database, to determine temporal and seasonal variations and to determine the contribution of motor vehicle traffic to the measured toxic substance concentrations. Ottawa is an appropriate choice of location for the measurement of motor vehicle related toxic and reactive compounds, as it has virtually no industrial sources that could be contributing to the ambient loadings. Samples were collected for a total of 165 volatile organic compounds and 25 carbonyl compounds. Sampling and analytical methodologyare discussed and results are presented. Toluene, ethylene andformaldehyde were the most abundant pollutants in Ottawa during both winter and summer. Total non-methane hydrocarbon concentrationwas measured as 100 μg m-3 at nose-level measurements in Ottawa.

Performance audits and laboratory comparisons for SCOS97-NARSTO measurements of speciated volatile organic compounds

Abstract Performance audits and laboratory comparisons were conducted as part of the quality assurance program for the 1997 Southern California Ozone Study (SCOS97-NARSTO) to document potential measurement biases among laboratories measuring speciated nonmethane hydrocarbons (NMHC), carbonyl compounds, halogenated compounds, and biogenic hydrocarbons. The results show that measurements of volatile organic compounds (VOC) made during SCOS97-NARSTO are generally consistent with specified data quality objectives. The hydrocarbon comparison involved nine laboratories and consisted of two sets of collocated ambient samples. The coefficients of variation among laboratories for the sum of the 55 PAM target compounds and total NMHC ranged from ±5 to 15 percent for ambient samples from Los Angeles and Azusa. Abundant hydrocarbons are consistently identified by all laboratories, but discrepancies occur for olefins greater than C 4 and for hydrocarbons greater than C 8 . Laboratory comparisons for halogenated compounds and biogenic hydrocarbons consisted of both concurrent ambient sampling by different laboratories and round-robin analysis of ambient samples. The coefficients of variation among participating laboratories were about 10–20 percent. Performance audits were conducted for measurement of carbonyl compounds involving sampling from a standard mixture of carbonyl compounds. The values reported by most of the laboratories were within 10–20 percent of those of the reference laboratory. Results of field measurement comparisons showed larger variations among the laboratories ranging from 20 to 40 percent for C 1 –C 3 carbonyl compounds. The greater variations observed in the field measurement comparison may reflect potential sampling artifacts, which the performance audits did not address.

Online Hourly Determination of 62 VOCs in Ambient Air: System Evaluation and Comparison with Another Two Analytical Techniques

This paper presents results of the processing and validation of data collected by an automatic gas chromato-graph (AGC). This system was used to monitor 62 volatile organic compounds (VOCs) in urban air in the Basque Country, Spain. The nonpolar compounds (C2–C10) identified—paraffins, olefins, aromatics, and chlorinated compounds—accounted for 88% of the mass of total non-methane hydrocarbons (TNMHCs) in ambient air. The evaluation of linearity, precision, detection limits (DLs), and stability of retention times (RTs) indicates that the equipment is suitable for measuring ambient air automatically for prolonged periods (6 months). The calibration of the equipment using response factors calculated on the basis of the effective carbon number (ECN) showed variations of over 10% for acetylene, isoprene, and n-hexane. The results provided by the automatic chromatograph correlated significantly with simultaneous results from other widely used techniques for determining VOCs in ambient air: (1) portable GC, equipped with photoionization detector (PID), and (2) active adsorption on Tenax-TA followed by thermal des-orption and chromatographic analysis.

Emissions of greenhouse gases and other airborne pollutants from charcoal making in Kenya and Brazil

Airborne emissions from charcoal‐making kilns commonly used in Kenya and Brazil were measured during typical operating conditions. Emission factors were determined for carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), carbon monoxide (CO), total nonmethane hydrocarbons, nitrogen oxides (NOx) and total suspended particulates (TSP) along with charcoal production efficiency and charcoal and fuelwood carbon and energy contents. The conversion of wood carbon to charcoal carbon ranged from 37 to 69%, depending on kiln type. Emission factors, expressed as grams of pollutant per kilogram of charcoal produced, for the eight kilns ranged from 543 to 3027 for CO2, 32–62 for CH4, 143–373 for CO, 24–124 for total nonmethane organic compounds, 0.011–0.30 for N2O, 0.0054–0.13 for NOx, and 13–41 for TSP. On average, fuelwood carbon was approximately diverted as follows: 51% to charcoal, 27% to CO2, and 13% to products of incomplete combustion (PIC). Due to the higher global warming potentials (GWPs) of PIC relative to CO2on a carbon atom basis, such kilns can produce rather large net greenhouse gas emissions, even when the wood is harvested renewably. Based on published GWPs for CO2, CH4, and N2O only, we estimate that 0.77–1.63 kg C‐CO2(carbon as carbon dioxide equivalents) is emitted per kilogram of charcoal produced. We estimate that the total primary global warming commitment (GWC) of Kenyan and Brazilian charcoal‐making kiln emissions is about 2.7 and 7.5 million tons (Mt) C‐CO2, respectively. For comparison, the primary GWC from fossil fuel use in the United States is almost 1700 Mt C‐CO2.

Volatile organic compound measurements in the California/Mexico border region during SCOS97

Measurements of volatile organic compounds (VOC) were carried out in the California/Mexico border region during the Southern California Ozone Study in the summer of 1997 (SCOS97). Integrated 3-h samples were collected in Rosarito (south of Tijuana, Mexico) and in Mexicali during intensive operational periods (IOP), twice per IOP day. VOC were collected using stainless-steel 6-l canisters; carbonyl compounds were collected using 2,4-dinitrophenylhydrazine (DNPH) impregnated C18 SepPak cartridges. The canister samples were analyzed for speciated volatile hydrocarbons (C 2–C 12), CO, CO 2, CH 4, methyl t-butyl ether (MTBE), and halogenated hydrocarbons. DNPH-impregnated cartridges were analyzed for 14 C 1–C 7 carbonyl compounds. The concentrations of all species were higher at Mexicali than in Rosarito. A good correlation between total non-methane hydrocarbons (TNMHC), CO, and other pollutants associated with motor vehicle emissions observed for Mexicali indicates that the main source of TNMHC at this site is vehicular traffic.

Atmospheric volatile organic compound measurements during the 1996 Paso del Norte Ozone Study

Ambient air VOC samples were collected at surface air quality monitoring sites, near sources of interest, and aloft on the US (El Paso) and Mexican (Ciudad Juárez) side of the border during a six-week period of the 1996 Paso del Norte Ozone Study. Samples were collected at five sites, three on the US side and two on the Mexican side, during nine intensive operation days when high ozone levels were forecast for the area. Six other sites were sampled to characterize up-wind, down-wind and other emission sources. Samples for determining source profiles were collected for rush hour traffic, propane-powered bus exhaust, automobile paint shop emissions, propane fuels, and industrial manufacturing in Cd. Juárez and a refinery in El Paso. Most samples were collected in electro-polished stainless steel canisters for determination of C 2 to C 10 + hydrocarbons by GC–FID. Carbonyl samples were collected on DNPH impregnated cartridges at three surface sites during aircraft flights and analyzed by HPLC. This paper presents the spatial and temporal characteristics of VOC species concentrations and compositions to examine the differences and similarities of the various locations and time periods. Overall surface, total non-methane hydrocarbon values ranged from 0.1 to 3.4 ppmC with the highest concentrations being recorded in the morning and evening at five vehicle-dominated sites, three in Cd. Juárez and two in El Paso. Toluene in El Paso samples and propane, which is used as a cooking and transportation fuel in Cd. Juárez, were the most abundant hydrocarbons. The most abundant carbonyls were acetaldehyde, acetone and formaldehyde.

Distribution and fate of selected oxygenated organic species in the troposphere and lower stratosphere over the Atlantic

A large number of oxygenated organic chemicals (peroxyacyl nitrates, alkyl nitrates, acetone, formaldehyde, methanol, methylhydroperoxide, acetic acid and formic acid) were measured during the 1997 Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (SONEX) airborne field campaign over the Atlantic. In this paper, we present a first picture of the distribution of these oxygenated organic chemicals (Ox‐organic) in the troposphere and the lower stratosphere, and assess their source and sink relationships. In both the troposphere and the lower stratosphere, the total atmospheric abundance of these oxygenated species (ΣOx‐organic) nearly equals that of total nonmethane hydrocarbons (ΣNMHC), which have been traditionally measured. A sizable fraction of the reactive nitrogen (10–30%) is present in its oxygenated organic form. The organic reactive nitrogen fraction is dominated by peroxyacetyl nitrate (PAN), with alkyl nitrates and peroxypropionyl nitrate (PPN) accounting for <5% of total NOy. Comparison of observations with the predictions of the Harvard three‐dimensional global model suggests that in many key areas (e.g., formaldehyde and peroxides) substantial differences between measurements and theory are present and must be resolved. In the case of CH3OH, there appears to be a large mismatch between atmospheric concentrations and estimated sources, indicating the presence of major unknown removal processes. Instrument intercomparisons as well as disagreements between observations and model predictions are used to identify needed improvements in key areas. The atmospheric chemistry and sources of this group of chemicals is poorly understood even though their fate is intricately linked with upper tropospheric NOx and HOx cycles.

Peroxyacetyl Nitrate in Atlanta, Georgia: Comparison and Analysis of Ambient Data for Suburban and Downtown Locations

ABSTRACT Peroxyacetyl nitrate (PAN) concentrations were measured at downtown and suburban locations in Atlanta, GA, in July and August 1992 as part of the SOS-SORP/ONA (Southern Oxidants Study–Southern Oxidants Research Program on Ozone Non-Attainment). PAN concentrations were generally higher at the downtown location than at the suburban location, but on days when the O3 concentration exceeded 80 ppbv, PAN concentrations were similar at both locations. On days when O3 did not exceed 80 ppbv, suburban PAN concentrations were much lower than downtown concentrations and resembled those reported for rural areas in the eastern United States. Regression analysis of PAN and O3 on NOx and total non-methane hydrocarbons (TNMHC) showed PAN to be most strongly dependent on morning NOx concentrations, while O3 was most dependent on morning TNMHC concentrations. NOx, PAN, and meteorological data from the suburban site were used in a one-dimensional transport model to estimate the accumulation rate of PAN to be ~1.5 x 106 molecules cm-3 sec-1. A simple kinetic model estimated peroxyacetyl radical concentrations to be ~0.5 pptv at the suburban location.