Gas and Particle Emissions from Automobile Tires in Laboratory and Field Studies

This paper is directed to air pollution scientists interested in special mobile emission sources. The purpose was to determine the contribution which automobile tires make to air pollution. The gaseous hydrocarbon and sulfur compounds emitted in laboratory tests were identified. Although these hydrocarbons can participate in smog reactions, their mass emission rate is less than 0.1 % of the current exhaust hydrocarbon emission rate. Hydrocarbons from tires are not measurable near a freeway. The particulate emitted from tires ranges in size from 0.01 μm to more than 30 μm, with the larger particles dominating the total mass. Measurements along a California freeway showed that most of the tire debris had settled within 5 m of the pavement edge. Airborne rubber concentrations were less than 0.5 μg/m³, or less than 5% of the total tire wear. These field measurements confirm the indoor emission pattern and verify that tire wear products are not a significant air pollution problem.     

Analysis of the Atmosphere for Light Hydrocarbons

A procedure has been developed for the analysis of trace quantities of light hydrocarbons in air. A freezetrap filled with chromatographic packing was installed in place of the gas sample loop of a flame ionization chromatograph. An air sample 0.1–0.5 liter volume was passed through the trap which was chilled with liquid oxygen. The trap wasthen brought to ice temperature and its contents simultaneously swept into the column. The resulting chrómatogram could be used to determine about 25 hydrocarbons through n-hexane. The minimum detectable concentration was below 1 ppb for these hydrocarbons. With such sensitivity it is possible to make useful measurements even on samples of light air pollution. Air samples from the Riverside area were analyzed in this fashion starting in the summer of 1965. The relative amounts of these hydrocarbons were then compared with the distribution reported for the various known hydrocarbon sources. The attenuation of the more reactive hydrocarbons by photolysis was also observed. A system for irradiating trapped air samples was also constructed. Samples were collected in 5-gallon borosilicate bottles which were then irradiated with ultraviolet radiation and the concentration changes followed.     

Gaseous Pollutants in St. Louis and Other Cities

During the fall of 1972, a study was undertaken to characterize gaseous air pollutants in the St. Louis metropolitan area. Information obtained in this study will be used in planning air pollution modeling studies to be carried out over the next 4 or 5 years under the Regional Air Pollution Study (RAPS) of the Environmental Protection Agency. From analyses of roadway samples, it was found that certain compounds in automotive emissions such as acetylene, carbon monoxide, o-xylene, ethylene, and 2-methylpentane occur in consistent proportions to other compounds. The concentrations of these indicator compounds in atmospheric samples were used to estimate the amounts of other hydrocarbons present that are attributable to automotive related emissions. Methane, ethane, and propane were found to originate principally from nonautomotive sources, both at St. Louis University and the St. Louis CAMP station. Similar concentrations were found in urban and non-urban areas. A comparison of ethylene-CO and propyl-ene-CO ratios in urban and non-urban areas indicates that CO can serve as an indicator of transport of urban pollutants. Sunlight irradiations of captured air samples showed increasing ozone production with increasing initial concentrations of hydrocarbons and nitrogen oxides. Substantial ozone and peroxyacetyl nitrate were formed from a total non-methane hydrocarbon concentration of only ¹/₄ ppm C.     

Direct Measurement of Fugitive Emissions of Hydrocarbons from a Refinery

Abstract

Refineries are a source of emissions of volatile hydrocarbons that contribute to the formation of smog and ozone. Fugitive emissions of hydrocarbons are difficult to measure and quantify. Currently these emissions are estimated based on standard emission factors for the type and use of equipment installed. Differential absorption light detection and ranging (DIAL) can remotely measure concentration profiles of hydrocarbons in the atmosphere up to several hundred meters from the instrument. When combined with wind speed and direction, downwind vertical DIAL scans can be used to calculate mass fluxes of the measured gas leaving the site. Using a mobile DIAL unit, a survey was completed at a Canadian refinery to quantify fugitive emissions of methane, C₂₊ hydrocarbons, and benzene and to apportion the hydrocarbon emissions to the various areas of the refinery. Refinery fugitive emissions as measured with DIAL during this demonstration study were 1240 kg/hr of C₂₊ hydrocarbons, 300 kg/hr of methane, and 5 kg/hr of benzene. Storage tanks accounted for over 50% of the total emissions of C₂₊ hydrocarbons and benzene. The coker area and cooling towers were also significant sources. The C₂₊ hydrocarbons emissions measured during the demonstration amounted to 0.17% of the mass of the refinery hydrocarbon throughput for that period. If the same loss were repeated throughout the year, the lost product would represent a value of US$3.1 million/yr (assuming US$40/bbl). The DIAL-measured hourly emissions of C₂₊ hydrocarbons were 15 times higher than the emission factor estimates and gave a different perspective on which areas of the refinery were the main source of emissions. Methods, such as DIAL, that can directly measure fugitive emissions would improve the effectiveness of efforts to reduce emissions, quantify the reduction in emissions, and improve the accuracy of emissions data that are reported to regulators and the public.     

Determination of the Detailed Hydrocarbon Composition and Potential Atmospheric Reactivity of Full-Range Motor Gasolines

The quantitative data obtained with a capillary GLC method, which is used to determine the individual C₃-C₁₂ hydrocarbons in full-range motor gasolines, have been employed in a computer program to calculate the hydrocarbon composition of the vapor in equilibrium with a gasoline at 100°F, as well as the equilibrium vapor-pressure of the gasoline at that temperature. The method used for computation is similar to that previously described by McEwen, assuming the gasoline to behave as an ideal liquid. Also calculated is the potential atmospheric reactivity of this equilibrium vapor relative to that from other gasolines when specific reactivity weighting factors for the individual hydrocarbons are employed. Calculated total vapor-pressure data agree well with experimental Reid vapor-pressure data obtained for typical premium-grade gasolines. Definite differences were observed in the relative potential atmospheric reactivities calculated at 100°F for the equilibrium vapors from the test gasolines.     

Quantitative ED-EPMA combined with morphological information for the characterization of individual aerosol particles collected in Incheon,Korea

A quantitative single-particle analytical technique, called low-Z particle electron probe X-ray microanalysis, combined with the utilization of their morphological information on individual particles, was applied to characterize six aerosol samples collected in one Korean city, Incheon, during March 9–15, 2006. The collected supermicron aerosol particles were classified based on their chemical species and morphology on a single-particle basis. Many different particle types were identified and their emission source, transport, and reactivity in the air were elucidated. In the samples, particles in the “soil-derived particles” group were the most abundant, followed by “reacted sea-salts”, “reacted CaCO₃-containing particles”, “genuine sea-salts”, “reacted sea-salts + others”, “Fe-containing particles”, “anthropogenic organics”, (NH₄)₂SO₄, “K-containing particles”, and “fly ash”. The application of this single-particle analysis, fully utilizing their chemical compositional and morphological data of individual particles, clearly revealed the different characteristics of the six aerosol samples. For samples S3 and S5, which were sampled during two Asian dust storm events, almost all particles were of soil origin that had not experienced chemical modification and that did not entrain sea-salts during their long-range transport. For sample S1, collected at an episodic period of high PM₁₀ concentration and haze, anthropogenic, secondary, and soil-derived particles emitted from local sources were predominant. For samples S2, S4, and S6, which were collected on average spring days with respect to their PM₁₀ concentrations, marine originated particles were the most abundant. Sample S2 seems to have been strongly influenced by emissions from the Yellow Sea and Korean peninsula, sample S4 had the minimum anthropogenic influence among the four samples collected in the absence of any Asian dust storm event, and sample S6 seems to have entrained air pollutants that had been transported from mainland China over the Yellow Sea to Korea.     

Los Angeles Gasoline Modification: Its Potential as an Air Pollution Control Measure

A joint project of government and industry people who studied the possible effect upon air pollution in Los Angeles of variations in the composition of gasoline sold in Los Angeles is discussed.

No experimental automotive test work was undertaken in this project. However, prototype fuel blends were made and analyzed in order to simulate the effects certain changes would have upon photochemical smog formation.

It is apparent from the results of this study that the potential of reducing smog in Los ngeles by fuel modifications is quite small, even in the year of maximum effect. This potential decreases to a negligible level due to the effectiveness of mechanical control of evaporative losses required in California starting with the 1970 model cars.     

Concentrations of volatile organic compounds in an industrial area of Korea

We measured and analyzed daily mean concentrations of volatile organic compounds (VOC) at Ulsan industrial and downtown sites from 3 to 8 June 1997. The industrial site is situated at the boundary of a petrochemical complex and the other is at downtown area in Ulsan. At each site, we collected ambient air samples in passivated stainless-steel containers by using constant flow samplers and analyzed them by a GC-FID. At Ulsan industrial site, the concentrations and their daily variations of total VOC were higher than those at the downtown site. The concentrations of oxygenated hydrocarbons were the highest among seven hydrocarbon groups at both sites. The fraction of C₂–C₅ light hydrocarbon concentrations to C₂–C₉ hydrocarbons at Ulsan industrial site was higher than that in other industrial areas. It suggests that fugitive emissions of light hydrocarbons in Ulsan industrial areas might be higher than those of other industrial areas. Under favorable wind conditions, the influence of industrial emissions of VOC on the downtown hydrocarbon levels was observed.     

Applications of Anthropogenic Lead ArchaeoStratigraphy (ALAS Model) to Hydrocarbon Remediation

A model, which employs the use of high precision stable lead isotopic analyses, has been developed to estimate the age of hydrocarbon releases. The ALAS Model (Anthropogenic Lead ArchaeoStratigraphy) is based on calibrated, systematic increases in lead isotope ratios of gasolines caused by shifts in sources of lead ores used by the U.S. lead industry, including manufacturers of alkylleads, to more radiogenic Mississippi Valley Type (MVT) deposits. Acquisition of high quality samples (free product, gasoline-impacted soil and groundwater) of known age and subsequent analyses of the hydrocarbon component by high precision lead isotopic analyses by thermal ionization mass spectrometry (TIMS) have produced the ALAS Model calibration curve. Age uncertainties range from  ± 1 to 2 years for gasoline releases which occurred between 1965 and 1990, the major era of leaded gasoline usage. Analytical methods required to measure lead isotope ratios on ∼5 nanograms of lead with precisions and accuracy of < ± 0.1% (2_SEM) are discussed in detail. Published lead isotopic measurements of gasoline-derived anthropogenic lead of samples throughout the United States are used to demonstrate the wide geographic range over which the ALAS Model may be applied. Two representative case studies involving an early 1970s free product release in California and the discrimination of a 1970s from modern unleaded gasoline release in Florida demonstrate the use of the model on single and multiple hydrocarbon releases, respectively, in different geographic regions of the United States. A third investigation focuses on the use of lead isotopes to correlate dissolved phase hydrocarbons with their source, in this case, unleaded (aka low lead) gasoline releases in New Jersey. Dissolved phase hydrocarbons (BTEX/MTBE) are shown to carry the lead isotopic signature of the unleaded gasoline into groundwater, allowing the specific source of the release to be identified. Investigations of lead isotopes as tracers of MTBE in groundwater are ongoing. However, both laboratory and field data indicate MTBE carries the lead isotopic signature of its unleaded gasoline source into groundwater, demonstrating the potential of the lead isotopic system as a discriminant of MTBE sources. Although developed to estimate the age of leaded gasoline releases, the ALAS Model has been successfully applied in studies requiring age dating of jet-A, diesel, kerosene, motor oil, and heating oil. These petroleum distillates are suspected of accidentally acquiring small, yet significant quantities of alkylleads during refining, allowing accurate ALAS Model ages to be determined. When lead levels in these petroleum distillates are within their normal range, typically tens to hundreds of ppb lead, it is possible to use lead isotopic ratios to correlate environmental releases of these products to their source or other releases.     

The Role of the Computer in Air Pollution Control

The search for ways of reducing vehicular emissions has led to numerous investigations of the relationships between fuel composition and the pollutants discharged from automobiles. The most obvious fuel effects result from evaporation of gasoline components from the fuel tanks and carburetors of vehicles which lack effective mechanical devices (such as those required on all 1971 model cars) to control evaporative losses. Thus, several laboratories and cooperative study groups (Coordinating Research Council and American Petroleum Institute) have investigated the ways in which fuel properties (especially the amounts and types of C₄-C₅ hydrocarbons) influence both the amount and the potential atmospheric reactivity of evaporative emissions.^1–6 But fuel evaporation accounts for only a small portion of the total hydrocarbons emitted by automobiles, and gasoline modifications (such as volatility reductions) that reduce evaporative losses can lead to higher levels of hydrocarbons in automobile exhaust.^4–6     

Careers in Air Pollution Control Plant Pathology

ABSTRACT

Profiles of the sources of nonmethane organic compounds (NMOCs) were developed for emissions from vehicles, petroleum fuels (gasoline, liquefied petroleum gas [LPG], and natural gas), a petroleum refinery, a smelter, and a cast iron factory in Cairo, Egypt. More than 100 hydrocarbons and oxygenated hydrocarbons were tentatively identified and quantified. Gasoline-vapor and whole-gasoline profiles could be distinguished from the other profiles by high concentrations of the C₅ and C₆ saturated hydrocarbons. The vehicle emission profile was similar to the whole-gasoline profile, with the exception of the unsaturated and aromatic hydrocarbons, which were present at higher concentrations in the vehicle emission profile. High levels of the C₂-C₄ saturated hydrocarbons, particularly n-butane, were characteristic features of the petroleum refinery emissions. The smelter and cast iron factory emissions were similar to the refinery emissions; however, the levels of benzene and toluene were greater in the former two sources. The LPG and natural gas emissions contained high concentrations of n-butane and ethane, respectively. The NMOC source profiles for Cairo were distinctly different from profiles for U.S. sources, indicating that NMOC source profiles are sensitive to the particular composition of petroleum fuels that are used in a location.     

Survey of volatile organic compounds associated with automotive emissions in the urban airshed of São Paulo,Brazil

The Metropolitan Region of São Paulo (MRSP), Brazil, is one of the largest metropolitan areas in the world (population 17 million, approx.) and relies heavily on alcohol-based fuels for automobiles. It is estimated that about 40% of the total volume of fuel is ethanol with some vehicles using pure ethanol and others a gasoline/ethanol blend. As such, São Paulo is an excellent example of an oxygenates-dominated airshed of mobile sources and is most likely indicative of the future in heavily populated areas in the US such as Los Angeles where “oxy-fuels” are becoming an important replacement for the conventional pure petroleum-based fuels. In this work, we surveyed the ambient air to identify and quantify the organic compounds associated with the evaporative and exhaust emissions of these fuels and to begin to understand the potential for human exposure. Because this was an initial test without detailed prior knowledge of the airshed of the area, we applied two different air sampling methods for various time periods to assess the ambient concentrations of a variety of polar and nonpolar volatile organic compounds (VOCs). For quality assurance (QA), we collected all the samples in duplicate (whole-air samples in Summa canisters and adsorbent-based samples on Perkin-Elmer Air Toxics tubes) at various flow rates to test performance. All samples were collected over identical time frames, typically for 1-, 2-, and 4-h periods per day at six different locations over a period of 1 week. Overall São Paulo results demonstrate that mean concentrations of single-ring aromatics are 2–3 times higher, volatile aldehydes are 5–10 times higher, and simple alcohols 10–100 times higher as compared to results of a recent study performed by EPA in the Los Angeles basin. C₄–C₁₁ n-alkanes were only slightly elevated in São Paulo.     

A Technique for Estimating the Age of Regular/Mid-grade Gasolines Released to the Subsurface Since the Early 1970's

Investigators, regulators, and litigants having interest in gasoline hydrocarbon releases are almost always concerned with knowing when a release occurred. Gasoline releases to the subsurface have, historically, been the most difficult to age date because of their volatile nature and highly aromatic composition. Age dating of gasolines in the past has depended on the degree of weathering of the lower boiling hydrocarbons in gasoline, the use and disuse of lead, lead isotopes, the use of other additives such as methyl-tertiary-butyl ether, and major refining and formulation changes. However, these approaches are limited and many times difficult to demonstrate and apply. This paper describes a new age dating technique using gas chromatographic data. It is based on the progressive enhancement of the aromatics and the reduction of the normal alkanes (paraffins) in the manufacture of regular and mid-grade gasolines since the 1970s. The changing composition of gasoline was necessary to maintain octane ratings during the removal of lead from the gasoline and while meeting increasingly stringent air quality regulations over the past 30 years. This paper proposes the use of an index that reflects these changes in gasoline composition over time and can be correlated to when the gasoline was manufactured. The resulting curve can be used to estimate the age of release (manufacture) of gasolines. This forensic application can be successfully applied to liquid gasoline samples where the evaporation of the gasoline is less than 50%. Case histories and examples are presented to demonstrate application of the technique.     

A Chemical Mass Balance for Volatile Organics in Chicago

Increasing attention to the presence of atmospheric volatile organic compounds has focused interest on the sources and fate of organics in ambient air. The purpose of this study was to develop a chemical mass balance receptor model (CMB) to determine the contributions of major organic pollution source types to ambient pollution levels. Twenty mid-day ambient air samples were analyzed for the presence of volatile hydrocarbons by gas chromatographlc procedures. Based on these measurements, contributions from vehicles, gasoline vapor emissions, and petroleum refineries to ambient organic concentrations were estimated. For the receptor site studied, vehicles were the dominant source type and accounted for 60.8 percent of the organics evaluated. Contributions from refineries, gasoline vapor, and all other sources were 10.1, 11.1, and 17.9 percent, respectively. Validation of the predictions showed that the model is sensitive to the effect of overall upwind emissions. The CMB model was shown to produce reasonable predictive results for vehicles, gasoline vapor, and refinery contributions to ambient non-methane organic concentrations.     

Polar and non-polar volatile organic compounds (VOCs) in urban Algiers and saharian sites of Algeria

For the first time, polar and non-polar organic compounds from C₄ to C₂₀ have been identified and quantified in one urban and two saharan sites located in Algeria. They were collected on adsorption traps filled with graphitic carbons and analyzed by high-resolution gas chromatography–mass spectrometry after thermal desorption. More than 190 compounds released by man-made and biogenic sources or formed in air by degradation of photochemical smog precursors were identified in the city center of Algiers. Some of them were never reported before. During our determinations, high levels of pollution characterized the city. Transport of anthropogenic pollutants together with some biogenic emission from date palm trees was mainly responsible for the levels of VOCs measured in Melika oasis located at the entrance of the Sahara desert. Background tropospheric levels of VOCs were instead detected in Bouchene sandy site of the Sahara desert where no biogenic sources were present.     

Applications of Anthropogenic Lead ArchaeoStratigraphy (ALAS Model) to Hydrocarbon Remediation

A model, which employs the use of high precision stable lead isotopic analyses, has been developed to estimate the age of hydrocarbon releases. The ALAS Model (Anthropogenic Lead ArchaeoStratigraphy) is based on calibrated, systematic increases in lead isotope ratios of gasolines caused by shifts in sources of lead ores used by the U.S. lead industry, including manufacturers of alkylleads, to more radiogenic Mississippi Valley Type (MVT) deposits. Acquisition of high quality samples (free product, gasoline-impacted soil and groundwater) of known age and subsequent analyses of the hydrocarbon component by high precision lead isotopic analyses by thermal ionization mass spectrometry (TIMS) have produced the ALAS Model calibration curve. Age uncertainties range from - 1 to 2 years for gasoline releases which occurred between 1965 and 1990, the major era of leaded gasoline usage. Analytical methods required to measure lead isotope ratios on ~5 nanograms of lead with precisions and accuracy of < - 0.1% (2 SEM ) are discussed in detail. Published lead isotopic measurements of gasoline-derived anthropogenic lead of samples throughout the United States are used to demonstrate the wide geographic range over which the ALAS Model may be applied. Two representative case studies involving an early 1970s free product release in California and the discrimination of a 1970s from modern unleaded gasoline release in Florida demonstrate the use of the model on single and multiple hydrocarbon releases, respectively, in different geographic regions of the United States. A third investigation focuses on the use of lead isotopes to correlate dissolved phase hydrocarbons with their source, in this case, unleaded (aka low lead) gasoline releases in New Jersey. Dissolved phase hydrocarbons (BTEX/MTBE) are shown to carry the lead isotopic signature of the unleaded gasoline into groundwater, allowing the specific source of the release to be identified. Investigations of lead isotopes as tracers of MTBE in groundwater are ongoing. However, both laboratory and field data indicate MTBE carries the lead isotopic signature of its unleaded gasoline source into groundwater, demonstrating the potential of the lead isotopic system as a discriminant of MTBE sources. Although developed to estimate the age of leaded gasoline releases, the ALAS Model has been successfully applied in studies requiring age dating of jet-A, diesel, kerosene, motor oil, and heating oil. These petroleum distillates are suspected of accidentally acquiring small, yet significant quantities of alkylleads during refining, allowing accurate ALAS Model ages to be determined. When lead levels in these petroleum distillates are within their normal range, typically tens to hundreds of ppb lead, it is possible to use lead isotopic ratios to correlate environmental releases of these products to their source or other releases.     

Effect of Gasoline Formulation on the Formation of Photosmog: A Box Model Study

Abstract

Based on exhaust gas analyses from the combustion of five different types of gasoline in a passenger car operated on a chassis dynamometer, box model simulations of the irradiation of exhaust/NO_x /air mixtures using an established chemical mechanism for a standardized photo-smog scenario were performed. The fuel matrix used covered wide fractional ranges for paraffinic, olefinic, and aromatic hydrocarbons. Two fuels also contained methyl tertiary butyl ether (MTBE). The different O₃ profiles calculated for each run were compared and interpreted. The O₃ levels obtained were strongly influenced by the exhaust gas concentrations of aromatic and olefinic hydro-carbons. The higher exhaust content of these compounds caused higher O₃ production in the smog system investigated. The conclusion of the present study is that the composition of gasoline cannot be taken directly for the estimation of the emissions’ O₃ creation potential from its combustion. Variation of the dilution in the different calculations showed evidence for an additional influence of transport effects. Accordingly, further detailed exhaust gas analyses followed by more complex modeling studies are necessary for a proper characterization of the relationship between fuel blend and gasoline combustion products.     

An historical experiment: Los Angeles smog evolution observed by blimp

Observations of smog over the Los Angeles Basin (LAB) links high oxidant mixing ratios with poor visibility, sometimes <5 km. By the 1970s, investigators recognized that most of the aerosol affecting visibility was from gaseous oxidation products, sulfate, nitrate, and organic carbon. This led to the 1972–1973 Aerosol Characterization Experiment (ACHEX), which included observations at the ground and from aircraft. Part of ACHEX was the measurement of smog by blimp in a Lagrangian-like format. The experiment on September 6, 1973, demonstrated that a blimp could travel with the wind across the LAB, observing ozone (O₃) and precursors, and particles of different size ranges. These included condensation nuclei (CN) concentrations dominated by particles of ≤ 0.1 µm diameter and light scattering coefficient (b_sc) representing mainly particles of 0.1–2.0 µm diameter. The results indicated a pollutant variation similar to that measured at a fixed site. Ozone was produced in an air mass, reaching a maximum of ~400 ppb in the presence of nitrogen oxides (NO_x) and nonmethane hydrocarbons (NMHCs), then declined. Although the photochemistry was developing, b_sc grew with O₃ mixing ratio to a quasi-steady state at ~9–10 × 10^?4 m^?1, decreasing in value much later with decease in O₃. The light scattering coefficient was found to be positively associated with the O₃ mixing ratio, whereas CN concentrations were negatively proportional to O₃ mixing ratio. The blimp experiment was supported with aircraft vertical profiles and ground-level observations from a mobile laboratory. The blimp flight obtained combined gas and particle changes aloft that could not be obtained by ground or fixed-wing aircraft measurements alone. The experiment was partially successful in achieving a true Lagrangian characterization of smog chemistry in a constrained or defined “open” air mass.

Implications: The Los Angeles experiment demonstrated the use of a blimp as a platform for measurement of air pollution traveling with an air mass across an urban area. The method added unique data showing the relationship between photochemical smog chemistry and aerosol dynamics in smog. The method offers an alternative to reliance on smog chamber and modeling observations to designing air quality management strategies for reactive pollutants.     

Estimates of the contributions of biogenic and anthropogenic hydrocarbons to secondary organic aerosol at a southeastern US location

An organic tracer-based method containing laboratory and field study components was used to estimate the secondary organic aerosol (SOA) contributions of biogenic and anthropogenic hydrocarbons to ambient organic carbon (OC) concentrations in PM_2.5 during 2003 in Research Triangle Park, NC. In the laboratory, smog chamber experiments were conducted where isoprene, α-pinene, β-caryophyllene, and toluene were individually irradiated in the presence of NO_X. In each experiment, SOA was collected and analyzed for potential tracer compounds, whose concentrations were used to calculate a mass fraction of tracer compounds for each hydrocarbon. In the field, 33 PM_2.5 samples were collected and analyzed for (1) tracer compounds observed in the laboratory irradiations, (2) levoglucosan, a biomass burning tracer, and (3) total OC. For each of the four hydrocarbons, the SOA contributions to ambient OC concentrations were estimated using the tracer concentrations and the laboratory-derived mass fractions. The estimates show SOA formation from isoprene, α-pinene, β-caryophyllene, and toluene contributed significantly to the ambient OC concentrations. The relative contributions were highly seasonal with biomass burning in the winter accounting for more than 50% of the OC concentrations, while SOA contributions remained low. However, during the 6-month period between May and October, SOA from the precursor hydrocarbons contributed more than 40% of the measured OC concentration. Although the tracer-based method is subject to considerable uncertainty due to the simplification of replacing the complex set of chemical reactions responsible for SOA with a laboratory-derived single-valued mass fraction, the results suggest this approach can be used to identify major sources of SOA which can assist in the development of air quality models.     

Identification of a potential source of chloroform in urban air: Preliminary Communication

A new potential source of elevated chloroform (CHCl₃) concentrations in urban air is reported. The exhaust gases from gasoline internal combustion engines operated on conventional “leaded” fuel and not equipped with catalytic converters contain parts-per-billion concentrations of chloroform which can, in congested urban areas, contribute significantly to the ambient concentration of chloroform. Exhaust gases from engines burning conventional “leaded” gasoline contain much higher levels of chloroform than do exhaust gases from engines equipped with catalytic converters and operating on “nonleaded” gasoline.