Roy B. Zweidinger

Real-world automotive emissions : Summary of studies in the Fort McHenry and Tuscarora Mountain Tunnels

Al~ract--Motor vehicle emission rates of CO, NO, NOx, and gas-phase speciated nonmethane hydrocarbons (NMHC) and carbonyl compounds were measured in 1992 in the Fort McHenry Tunnel under Baltimore Harbor and in the Tuscarora Mountain Tunnel of the Pennsylvania Turnpike, for comparison with emission-model predictions and for calculation of the reactivity of vehicle emissions with respect to 03 formation. Both tunnels represent a high-speed setting at relatively steady speed. The cars at both sites tended to be newer than elsewhere (median age was < 4 yr), and much better maintained as judged by low CO/CO2 ratios and other emissions characteristics. The Tuscarora Mountain Tunnel is flat, making it advantageous for testing automotive emission models, while in the underwater Fort McHenry Tunnel the impact of roadway grade can be evaluated. MOBILE4.1 and MOBILE5 gave predictions within + 50% of observation most of the time. Tbere was a tendency to overpredict, especially with MOBILE5 and especially at Tuscarora. However, fight-dutyvehicle CO, NMHC, and NOx all were underpredicted by MOBILE4.1 at Fort McHenry. Light-dutyvehicle CO/NO~ ratios and NMHC/NO~ ratios were generally a little higher than predicted. The comparability of the predictions to the observations contrasts with a 1987 experiment in an urban tunnel (Van Nuys) where CO and HC, as well as CO/NO~ and NMHC/NO~ ratios, were grossly underpredicted. The effect of roadway grade on gram per mile (g mi- 1) emissions was substantial. Fuel-specific emissions (g gal-1), however, were almost independent of roadway grade, which suggests a potential virtue in emissions models based on fuel-specific emissions rather than g mi- 1 emissions. Some 200 NMHC and carbonyl emissions species were quantified as to their light- and heavy-dutyvehicle emission rates. The heavy-duty-vehicle NMHC emissions were calculated to possess more reactivity, per vehicle-mile, with respect to 03 formation (g 03 per vehicle-mile) than did the light-duty-vehicle NMHC emissions. Per gallon of fuel consumed, the light-duty vehicles had the greater reactivity. Much of the NMHC, and much of their reactivity with respect to O3 formation, resided in compounds heavier than Cto, mostly from beavy-duty diesels, implying that atmospheric NMHC sampling with canisters alone is inadequate in at least some situations since canisters were found not to be quantitative beyond ~ C1o. The contrasting lack of compounds heavier than C1o from light-duty vehicles suggests a way to separate light- and heavy-duty-vehicle contributions in receptor modeling source apportionment. The division between light-duty-vehicle tailpipe and nontaiipipe NMHC emissions was ~ 85% tailpipe and ~ 15% nontailpipe (evaporative running losses, etc.). Measured CO/CO2 ratios agreed well with concurrent roadside infrared remote sensing measurements on light-duty vehicles, although remote sensing HC/CO2 ratio measurements were not successful at the low HC levels prevailing. Remote sensing measurements on heavy-duty diesels were obtained for the first time, and were roughly in agreement with the regular (bag sampling) tunnel measurements in both CO/CO2 and HC/CO2 ratios. A number of recommendations for further experiments, measurement methodology development, and emissions model development and evaluation are offered. Copyright

Distinguishing the Contributions of Residential Wood Combustion and Mobile Source Emissions Using Relative Concentrations of Dimethylphenanthrene Isomers

As part of the United States Environmental Protection Agencys Integrated Air Cancer Project, air particulate matter samples collected in Boise, ID, were analyzed by gas chromatography with mass spectrometric detection (GC-MS) and apportioned between their two main sources : residential wood combustion (RWC) and motor vehicle (MV) emissions. The technique used for distinguishing the source contributions involved comparison of the concentration of 1,7-dimethylphenanthrene (1,7-DMP), a polycyclic aromatic hydrocarbon (PAH) emitted primarily by burning soft woods (e.g., pines), with that of a PAH emitted in modest concentrations by both RWC and MV sources, 2,6-dimethylphenanthrene (2,6-DMP). These results were then compared with the mean 1,7-DMP/2,6-DMP ratio of 48 samples collected in a roadway tunnel, with any enrichment in the Boise sample ratios over the mean tunnel ratio attributable to the RWC source. These resulting RWC contributions were compared with fraction RWC results obtained by radiocarbon measurements ( 14 C/ 13 C) of the same extracts from Boise, with generally good correlations between the two techniques observed, suggesting that the methods are comparable when used to distinguish emissions of MVs from RWC of soft woods.

The 1998 Baltimore Particulate Matter Epidemiology-Exposure Study: Part 1. Comparison of Ambient, Residential Outdoor, Indoor and Apartment Particulate Matter Monitoring

A combined epidemiological–exposure panel study was conducted during the summer of 1998 in Baltimore, Maryland. The objectives of the exposure analysis component of the 28-day study were to investigate the statistical relationships between particulate matter (PM) and related co-pollutants from numerous spatial boundaries associated with an elderly population, provide daily mass concentrations needed for the epidemiological assessment, and perform an extensive personal exposure assessment. Repeated 24-h integrated PM2.5 (n=394) and PM10 (n=170) data collections corresponding to stationary residential central indoor, individual apartment, residential outdoor and ambient monitoring were obtained using the same sampling methodology. An additional 325 PM2.5 personal air samples were collected from a pool of 21 elderly (65+ years of age) subjects. These subjects were residents of the 18-story retirement facility where residential monitoring was conducted. Mean daily central indoor and residential apartment concentrations were approximately 10 µg/m3. Outdoor and ambient PM2.5 concentrations averaged 22 µg/m3 with a daily range of 6.7–59.3 µg/m3. The slope of the central indoor/outdoor PM2.5 mass relationship was 0.38. The average daily ratio of PM2.5/PM10 mass co ncentrations across the measurement sites ranged from 0.73 to 0.92. Both the central indoor and mean apartment PM2.5 mass concentrations were highly correlated with the outdoor variables (r>0.94). The lack of traditionally recognized indoor sources of PM present within the facility might have accounted for the high degree of correlation observed between the variables. Results associated with the personal monitoring effort are discussed in depth in Part 2 of this article.

The 1998 Baltimore Particulate Matter Epidemiology–Exposure Study: Part 2. Personal exposure assessment associated with an elderly study population

An integrated epidemiological–exposure panel study was conducted during the summer of 1998 which focused upon establishing relationships between potential human exposures to particulate matter (PM) and related co-pollutants with detectable health effects. The study design incorporated repeated individual 24-h integrated PM2.5 personal exposure monitoring. A total of 325 PM2.5 personal exposure samples were obtained during a 28-day study period using a subject pool of 21 elderly (65+ years of age) residents of an 18-story retirement facility near Baltimore, Maryland. Each sample represented a unique 24-h breathing zone measurement of PM2.5 mass concentration. PM2.5 and PM10 mass concentrations collected from the apartments of the subjects as well as residential and ambient sites were compared to individual and mean PM2.5 personal exposures. Daily PM2.5 personal exposure concentrations ranged from 2.4 to 47.8 µg/m3 with an overall individual study mean of 12.9 µg/m3. Mean PM2.5 personal exposures were determined to be highly correlated to those representing the central indoor (r=0.90) and ambient sites (r=0.89). Subjects reported spending an average of 92% of each day within the confines of the retirement center. Based upon measured and modeled exposures, a mean PM2.5 personal cloud of 3.1 µg/m3 was estimated. Data collected from these participants may be unique with respect to the general elderly population due to the communal lifestyle within the facility and reported low frequency of exposure to sources of PM.

Detailed hydrocarbon and aldehyde mobile source emissions from roadway studies.

A field study was conducted along US Highway 70 near Raleigh, NC, to evaluate methods for estimating emission factors and, in particular, for determining volatile organic carbon (VOC) species emitted from traffic. Integrated samples were collected 1m from the roadway between 7:30 and 8:30 a.m. at four different roadside locations representing various combinations of traffic conditions. The light-duty traffic component (>90%) was classified by model year between 1975 and 1983. On a percent of total non-methane basis,the distribution of VOCs varied little between sampling sites. The roadside VOC distribution was compared to dynamometer/dilution tube test results on in-use vehicles, which were weighted to reflect the same model year distribution observed on the roadway. Some of the differences seen were attributed to fuel effects, while others may reflect an insufficient data base. Mass emission rates calculated from release of a tracer gas by a pace car varied unpredictably and were higher than those calculated by the Mobile3 model or observed with the in-use vehicle dynamometer data.

Mutagenicity and chemical characteristics of carbonaceous particulate matter from vehicles on the road.

Experiments were conducted in the Allegheny Mountain Tunnel of the Pennsylvania Turnpike in 1979 to evaluate bacterial mutagenicities of particulate emissions from heavy-duty diesels and gasoline-powered vehicles in highway operation. Filter samples were extracted with dichloromethane followed by acetonitrile. Ames assays with and without microsomal activation, HPLC fluorescence profiles, GC molecular weight distributions, and particle size distributions were obtained. We find that (1) the diesel particulate matter at Allegheny resembles that encountered in dilution-tube studies by all criteria studied (particulate mass emission rate, extractability, particle size, extract HPLC profile, extract molecular weight distribution, and mutagenicity--though these findings do not preclude the possibility of substantial differences in detailed chemical properties), (2) in revertants per microgram of dichloromethane-extracted material at Allegheny, the mutagenicities of the diesel particulate matter and of the local rural ambient particulate matter are of the same order of magnitude, and (3) in revertants per kilometer traveled, the mutagenicity of particulate emissions from heavy-duty diesels is several times (median approx.6 times) that of emissions from gasoline-powered vehicles.

Comparison of PM2.5 and PM10 monitors.

An extensive PM monitoring study was conducted during the 1998 Baltimore PM Epidemiology-Exposure Study of the Elderly. One goal was to investigate the mass concentration comparability between various monitoring instrumentation located across residential indoor, residential outdoor, and ambient sites. Filter-based (24-h integrated) samplers included Federal Reference Method Monitors (PM2.5-FRMs), Personal Environmental Monitors (PEMs), Versatile Air Pollution Samplers (VAPS), and cyclone-based instruments. Tapered element oscillating microbalances (TEOMs) collected real-time data. Measurements were collected on a near-daily basis over a 28-day period during July–August, 1998. The selected monitors had individual sampling completeness percentages ranging from 64% to 100%. Quantitation limits varied from 0.2 to 5.0 µg/m3. Results from matched days indicated that mean individual PM10 and PM2.5 mass concentrations differed by less than 3 µg/m3 across the instrumentation and within each respective size fraction. PM10 and PM2.5 mass concentration regression coefficients of determination between the monitors often exceeded 0.90 with coarse (PM10–2.5) comparisons revealing coefficients typically well below 0.40. Only one of the outdoor collocated PM2.5 monitors (PEM) provided mass concentration data that were statistically different from that produced by a protoype PM2.5 FRM sampler. The PEM had a positive mass concentration bias ranging up to 18% relative to the FRM prototype.

Sources of genotoxicity and cancer risk in ambient air

Products of incomplete combustion are identified as a major source of carcinogenic risk in urban areas, especially those from small non-industrial sources. The major ubiquitous emission sources outdoors in populated areas are residential home heating and motor vehicles. Indoors the major combustion source is environmental tobacco smoke. Polycyclic organic matter adsorbed onto the particles emitted from incomplete combustion are estimated to make the largest contribution to human genotoxic and cancer risk. Mutagenic emission factors combined with dispersion modelling indicated that automobiles and heating sources were major sources of mutagens. Ambient air studies to apportion the sources of mutagens in non-industrial areas confirmed this prediction. To apportion and estimate the cancer risk of ambient organic matter from particles in vivo animal tumour data, receptor modelling and human exposure data were combined. Tumourigenicity studies of the source apportioned ambient organic matter provided the relative tumour potencies of two ambient samples of different source composition. The human cancer unit risks were developed based on the comparative potency method using tumour data from these ambient samples. Residential wood combustion accounted for 75% of the exposure to particle associated organics, but only 20% of the estimated cancer risk. The remaining 80% of the risk appears to be associated with the mobile source component and atmospheric transformation products from these source emissions.

A comparative assessment of Boise, Idaho, ambient air fine particle samples using the plate and microsuspension Salmonella mutagenicity assays

The primary objective of this study is to characterize the genotoxic potential of the ambient air aerosols collected within an air shed impacted primarily by wood smoke and automotive emissions. The study also examines the relative merits of a microsuspension assay and the standard plate assay for monitoring the presence of airborne particle-bound mutagens. Wintertime ambient air particulate samples collected from Boise, Idaho, USA, were shown to contain extractable organic matter that is mutagenic in the Salmonella typhimurium microsuspension and plate-incorporation assays. Differences in the results from the primary sites, auxiliary sites and the background site demonstrate that the particle-bound mutagens are not evenly distributed within the air shed and are more associated with the location of sampling than with the time of sampling or the type of bioassay used to evaluate the samples. This study also demonstrates that the bioassay protocol used in such studies should depend upon the characteristics of the air sheds mutagens and the purpose of the study. For example, the microsuspension assay gave somewhat more variable results between samples but was approximately threefold more sensitive than the plate assay. When strain TA98 was used in the microsuspension assay, the mutagenic response was greater without an exogenous activation system. The reverse was true for the plate assay in which the use of an exogenous activation system increased the mutagenicity response. TA100 in the microsuspension assay provided results comparable to those with TA98. This is important because TA100 can also be used to bioassay semivolatile and volatile organics associated with ambient air mutagenicity. This, in turn, allows a comparison of the mutagenicity of organics collected by differing methods due to their volatility. Future studies should be directed toward correlation of mutagenicity results with other analytical results in order to further develop methods for better characterization of the genotoxicity of ambient air.

Selection of a suitable extraction method for mutagenic activity from woodsmoke-impacted air particles

Abstract Extraction methods were evaluated for recovery of mutagenic activity from woodsmoke-impacted air particles. Soxhlet and sonication techniques were utilized with a variety of solvents to ascertain the effect of solvent choice, extraction methods, or dissolved gases in extraction solvents on the recovery of mutagenicity. Sonication extraction gave slightly less mass recovery than the Soxhlet method. Methanol extracted more mass than the other solvents with dichloromethane recovering the least. Dissolved gases were not found to have any effect, while mutagenicity was shown to be dependent upon solvent and extraction method. Soxhlet extraction with acetone and toluene/ethanol yielded the highest recovery of mutagenic activity, however, results indicated a solvent/solute interaction which chemically altered one or