Contribution Of Mobile Sources Research Articles

Ecological safety of the urbanized territories under conditions of technogenic transformation of atmospheric precipitations

Formation conditions of ecological hazard of urbanized territories under the influence of atmospheric precipitations are analyzed in the paper. Self-consistent control scheme of ecological safety of precipitations is developed. It includes the stages of identification of hazards, formation of databases and making managerial decisions. The analysis of identification features of hazardous factors that cause ecologically hazardous precipitations is conducted. The features of atmospheric precipitations as the object of the ecological safety assessment are described. The choice of acidity index of precipitations in the city of Chernivtsi as an environmental hazard indicator is justified. The model scheme of interaction of natural and anthropogenic factors in the formation of ecologically hazardous sediments is developed. The influence of wind conditions on the environmental safety of precipitations is determined. In particular, it is shown that, in Chernivtsi north-west winds have the greatest influence on the formation of the ecological hazard of atmospheric precipitations. The contribution of stationary and mobile sources to the technogenic transformation of precipitations is analyzed. The role of transport networks and automotive pollution in the formation of roadside areas of high ecological hazard of precipitations is shown. It is found that, in Chernivtsi contribution of mobile sources to the overall picture of air pollution is consistently high and ranges from 91,6-92,3 %. Herewith, 60.4 % of the total emissions of sulfur oxides, 93 % of nitrogen oxides and 97.4 % of carbon oxide is formed due to mobile sources. This in turn leads to the formation of local areas of environmentally hazardous precipitations.

Analysis of mobile source air toxics (MSATs)—Near-road VOC and carbonyl concentrations

Exposures to mobile source air toxics (MSATs) have been associated with numerous adverse health effects. While thousands of air toxic compounds are emitted from mobile sources, members of a subset of compounds are considered high priority due to their significant contribution to cancer and noncancer health risks and the contribution of mobile sources to total exposure as evaluated by the U.S. Environmental Protection Agency (EPA) National-Scale Air Toxics Assessments (NATA). These pollutants include benzene, 1,3-butadiene, ethylbenzene, acrolein, acetaldehyde, formaldehyde, naphthalene, polycyclic organic matter, and diesel particulate matter/organic gases. This study provided year-long trends of benzene, 1,3-butadiene, acrolein, acetaldehyde, and formaldehyde in Las Vegas, NV. Results indicated that MSAT concentrations often did not exhibit trends typical of other primary emitted pollutants in this study. Instead, other mobile sources beyond the highway of interest contributed to the measured values, including a major arterial road, a large commercial airport, and a nearby parking lot. The data were compared with relevant census-tract NATA estimates, with estimated ambient 1,3-butadiene concentrations similar to the measured values. Measured benzene values were much lower relative to the NATA total ambient benzene concentrations. Measured acrolein values were much higher relative to the NATA total acrolein concentrations. Measured acetaldehyde and formaldehyde values were also higher relative to the NATA total acetaldehyde and formaldehyde concentrations for all wind conditions and downwind conditions. Some possible explanations for these differences include nearby sources influencing the measured values; meteorological influences that may not be well captured by the NATA modeling regime; chemical reactivity of measured compounds; and additional explanatory variables may be needed for certain urban areas in order to accurately disaggregate anthropogenic air toxics emissions. Implications: Comparison of air toxics concentrations measured at four long-term near-road sites in Las Vegas, NV, show generally good agreement with the EPA 2005 NATA total ambient concentrations. Measured concentrations did not compare as well with EPA 2005 NATA for the on-road mobile portion of the ambient concentrations. This highlights the complexity of air toxic emission sources and impacts in urban areas, especially around large highway facilities; NATA's inability to capture local-scale meteorology and fine-scale ambient gradients; and that additional explanatory variables may be needed for certain urban areas in order to accurately disaggregate anthropogenic air toxics emissions.

Quantitative evaluation of emission controls on primary and secondary organic aerosol sources during Beijing 2008 Olympics

Abstract. To assess the primary and secondary sources of fine organic aerosols after the aggressive implementation of air pollution controls during the 2008 Beijing Olympic Games, 12 h PM2.5 values were measured at an urban site at Peking University (PKU) and an upwind rural site at Yufa during the CAREBEIJING-2008 (Campaigns of Air quality REsearch in BEIJING and surrounding region) summer field campaign. The average PM2.5 concentrations were 72.5 ± 43.6 μg m−3 and 64.3 ± 36.2 μg m−3 (average ± standard deviation, below as the same) at PKU and Yufa, respectively, showing the lowest concentrations in recent years. Combining the results from a CMB (chemical mass balance) model and secondary organic aerosol (SOA) tracer-yield model, five primary and four secondary fine organic aerosol sources were compared with the results from previous studies in Beijing. The relative contribution of mobile sources to PM2.5 concentrations was increased in 2008, with diesel engines contributing 16.2 ± 5.9% and 14.5 ± 4.1% and gasoline vehicles contributing 10.3 ± 8.7% and 7.9 ± 6.2% to organic carbon (OC) at PKU and Yufa, respectively. Due to the implementation of emission controls, the absolute OC concentrations from primary sources were reduced during the Olympics, and the contributions from secondary formation of OC represented a larger relative source of fine organic aerosols. Compared with the non-controlled period prior to the Olympics, primary vehicle contributions were reduced by 30% at the urban site and 24% at the rural site. The reductions in coal combustion contributions were 57% at PKU and 7% at Yufa. Our results demonstrate that the emission control measures implemented in 2008 significantly alleviated the primary organic particle pollution in and around Beijing. However, additional studies are needed to provide a more comprehensive assessment of the emission control effectiveness on SOA formation.

Source apportionment and organic compound characterization of ambient ultrafine particulate matter (PM) in the Los Angeles Basin

In this study, quasi-UFP (PM0.25, dp < 0.25 μm) were collected for 24 h once per week from April 2008 to March 2009 at 10 different locations in the Los Angeles Basin. Samples were chemically analyzed and organic constituents of PM0.25 were grouped into polycyclic aromatic hydrocarbon (PAHs), hopanes and steranes, n-alkanes, and levoglucosan, with concentration levels ranging from 0.16 to 5.5, 0.09 to 2.2, 9.3 to 48, and 2.2 to 106.2 ng m−3 over all sites and seasons, respectively. A molecular marker-based chemical mass balance (MM-CMB) model was applied to estimate the relative contributions from the following primary sources: mobile sources (combined gasoline and diesel vehicles), wood smoke, natural gas combustion, vegetative detritus, and ship emissions. Secondary organic aerosol (SOA) tracers were not included in the model; however their contributions were estimated from non-biomass burning water soluble organic carbon (WSOCnb) and un-apportioned OC from MM-CMB model (“other OC”). High correlation (R2 = 0.8) between “other OC” and WSOCnb in summer suggests that “other OC” is highly impacted by SOA, however un-apportioned primary sources may contribute to “other OC” as well. Mobile sources were expectedly the major primary contributor to PM0.25, with seasonal average contributions of 31 ± 12% in summer and 57 ± 17% in winter. “Other organic matter” was the second largest contributor to PM0.25 in all seasons, across the basin, with substantially higher contribution during warmer spring and summer seasons (27%), while lowest during cold seasons (13%). Wood smoke was the third major contributor to PM0.25 in winter, whereas its contribution was lowest in summer. As expected, ship emissions displayed the highest contribution at the near-harbor HUD site, and their levels continually decreased as a function of distance from coast. Two other primary sources, vegetative detritus and natural gas combustion, collectively contributed to 1.3 ± 0.8% of PM0.25 on an annual average basis over all sites. Comparison of our results to PM2.5 OC apportionment, conducted at central LA, shows that contribution of mobile sources to PM0.25 OC is more than two times higher than PM2.5 (75% and 30%, respectively), while “other OC” contributed significantly higher to PM2.5 OC compared to PM0.25 (56% and 21%, respectively).

Particulate matter source apportionment in Cairo: recent measurements and comparison with previous studies

This paper presents results of an atmospheric particulate matter (PM) monitoring and source apportionment study conducted during summer and fall 2010 in Cairo. These results are compared to those of similar studies in 1999 and 2002. Concentrations of PM2.5 and PM10 mass and their chemical constituents were determined and chemical mass balance modeling was conducted to estimate the source contributions to ambient PM. Emphasis was placed on characterizing the long-term trends in atmospheric lead (Pb) concentrations and their sources in Cairo. PM2.5 and PM10 concentrations were highest during fall 1999 at four of the five study sites. This was also the case for open (vegetative/trash) burning contributions, which showed a smaller increase during fall 2010. Burning of agricultural waste after the fall harvest continues to be a major source of PM in Cairo. Both PM2.5 and PM10 mass decreased dramatically at Shobra, an industrial site, from 1999 to 2010. A reduction of lead smelting has resulted in a decrease of ambient Pb concentrations of up to two orders of magnitude from 1999 to 2010 at Shobra, El-Zamalek, and El-Qualaly. From 1999 to 2010, the mobile source contribution has been relatively stable at most of the study sites. Future efforts to reduce ambient PM should focus on controlling emissions from motor vehicles and open burning and implementing mitigation strategies for reducing resuspended road and construction dust.

Mobile Source and Livestock Feed Contributions to Regional Ozone Formation in Central California

A three-dimensional air quality model with 8 km horizontal resolution was applied to estimate the summertime ozone (O(3)) production from mobile sources and fermented livestock feed in California's San Joaquin Valley (SJV) during years 2000, 2005, 2010, 2015, and 2020. Previous studies have estimated that animal feed emissions of volatile organic compounds (VOCs) have greater O(3) formation potential than mobile-source VOC emissions when averaging across the entire SJV. The higher spatial resolution in the current study shows that the proximity of oxides of nitrogen (NO(x)) and VOC emissions from mobile sources enhances their O(3) formation potential. Livestock feed VOC emissions contributed 3-4 ppb of peak O(3) (8-h average) in Tulare County and 1-2 ppb throughout the remainder of the SJV during the CCOS 2000 July-August episode. In total, livestock feed contributed ~3.5 tons of the ground level peak O(3) (8 h average) in the SJV region, and mobile VOC contributed ~12 tons in this episode. O(3) production from mobile sources is declining over time in response to emissions control plans that call for cleaner fuels and engines with advanced emissions controls. Projecting forward to the year 2020, mobile-source VOC emissions are predicted to produce ~3 tons of the ground level peak O(3)(8-h average) and livestock feed VOC emissions are predicted to contribute ~2.5 tons making these sources nearly equivalent.

Noise impact in a residential development in Zapopan Jalisco, Mexico.

Altagracia is a residential development in Zapopan Jalisco. Here noise due to stationary and mobile sources is an important environmental stressor, since the settlement is close to industry complexes and the major periphery road of the metropolis. As a way of getting knowledge about what noise sources contribute the most to the noise impact within the development, a noise environmental assessment was performed. 14 samples were taken to evaluate the contribution of mobile and stationary sources. Sampling sites were established as a result of a pilot experiment at which the highest noise levels were recorded. Data processing and analysis were performed taking into account national standards for stationary sources (NOM 081-ECOL-94), and mean values for the mobile sources, since there is not specific regulation for them. Results of the study, highlights mobile sources as the major contributor of noise impact within the residential area.

Spatial variability of carbonaceous aerosols and associated source tracers in two cites in the Midwestern United States

Semi-continuous and 24-h averaged measurements of fine carbonaceous aerosols were made concurrently at three sites within each of two U.S. Midwestern Cities; Detroit, Michigan and Cleveland, Ohio; during two, one-month intensive campaigns conducted in July of 2007 and January & February of 2008. A comparison of 24-h measurements revealed substantial intra-urban variability in carbonaceous aerosols consistent with the influence of local sources, and excesses in both PM 2.5 organic carbon (OC) and elemental carbon (EC) were identified at individual sites within each city. High time-resolved black carbon (BC) measurements indicated that elemental carbon concentrations were higher at sites adjacent to freeways and busy surface streets, and temporal patterns suggested that excess EC at sites adjacent to freeways was dominated by mobile source emissions while excesses in EC away from traffic corridors was dominated by point/area source emissions. The site-to-site variability in OC concentrations was approximately 7% within the neighborhood scale (0.5–4 km) and between 4 and 27% at the urban scale (4–100 km). In contrast, measurements of organic source tracers, in conjunction with a Chemical Mass Balance (CMB) source-apportionment model, indicated that the spatial variation in the contribution of both mobile and stationary sources to PM 2.5 OC often exceeded the variation in OC mass concentration by a factor of 3 or more. Markers for mobile sources, biomass smoke, natural gas, and coal combustion differed by as much as 60% within the neighborhood scale and by greater than 200% within the urban scale. The observations made during this study suggest that the urban excess of carbonaceous aerosols is much more complex than has been previously reported and that a more rigorous, source-oriented approach should be taken in order to assess the risk associated with exposure to carbonaceous aerosols within the industrialized environments of the Midwestern United States.

Real-World Vehicle Emissions: A Summary of the 18th Coordinating Research Council On-Road Vehicle Emissions Workshop

The Coordinating Research Council (CRC) convened its 18th On-Road Vehicle Emissions Workshop March 31– April 2, 2008, with 104 presentations describing the most recent mobile source-related emissions research. In this paper we summarize the presentations from researchers whose efforts are improving our understanding of the contribution of mobile sources to air quality. Participants in the workshop discussed emission models and emissions inventories, results from gas- and particle-phase emissions studies from spark-ignition and diesel-powered vehicles (with an emphasis in this workshop on particle emissions), effects of fuels on emissions, evaluation of in-use emission-control programs, and efforts to improve our capabilities in performing on-board emissions measurements, as well as topics for future research.

Sources of volatile organic compounds in Cairo’s ambient air

The greater Cairo area suffers from extreme levels of gas and particulate phase air pollutants. In order to reduce the levels of ambient pollution, the USAID and the Egyptian Environmental Affairs Agency (EEAA) have supported the Cairo Air Improvement Project (CAIP). As part of this project, two intensive ambient monitoring studies were carried out during the period of February 22 to March 4 and October 27 to November 27, 1999. Volatile organic compounds (VOCs) were measured on a 24-h basis at six sampling stations during each of the intensive periods. During the February/March study, samples were collected daily, while in the October/November study samples were collected every other day. The six intensive measurement sites represented background levels, mobile source impacts, industrial impacts, and residential exposure. High levels of NMHC were observed at all locations. NMHC concentrations ranged from 365 ppb C at Helwan to 1,848 ppb C at El Qualaly during winter, 1999 and from 461 ppb C at Kaha to 2,037 ppb C at El Qualaly during fall, 1999. El Qualaly, the site chosen to represent mobile emissions, displayed the highest average NMHC concentrations of any site, by a factor of 2 or more. The highest mobile source contributions were estimated at this site. The major contributors to NMHC at all sites were mobile emissions, lead smelting, and compressed natural gas.

Real-World Vehicle Emissions: A Summary of the Seventeenth Coordinating Research Council On Road Vehicle Emissions Workshop

The Coordinating Research Council, Inc. (CRC) held its 17th On-Road Vehicle Emissions Workshop in March 2007, where results of the most recent on-road vehicle emissions research were presented. We summarize ongoing work from researchers who are engaged in improving our understanding of the role and contribution of mobile sources to ambient air quality and emission inventories. Participants in the Workshop discussed efforts to improve mobile source emission models, light- and heavy-duty vehicle emissions measurements, on- and off-road emissions measurements, effects of fuels and lubricating oils on emissions, as well as emerging issues and topics for future research.

Assessment of diesel particulate matter exposure in the workplace: freight terminals

A large study has been undertaken to assess the exposure to diesel exhaust within diesel trucking terminals. A critical component of this assessment is an analysis of the variation in carbonaceous particulate matter (PM) across trucking terminal locations; consistency in the primary sources can be effectively tracked by analyzing trends in elemental carbon (EC) and organic molecular marker concentrations. Ambient samples were collected at yard, dock and repair shop work stations in 7 terminals in the USA and 1 in Mexico. Concentrations of EC ranged from 0.2 to 12 microg m(-3) among the terminals, which corresponds to the range seen in the concentration of summed hopanes (0.5 to 20.5 ng m(-3)). However, when chemical mass balance (CMB) source apportionment results were presented as percent contribution to organic carbon (OC) concentrations, the contribution of mobile sources to OC are similar among the terminals in different cities. The average mobile source percent contribution to OC was 75.3 +/- 17.1% for truck repair shops, 65.4 +/- 20.4% for the docks and 38.4 +/- 9.5% for the terminal yard samples. A relatively consistent mobile source impact was present at all the terminals only when considering percentage of total OC concentrations, not in terms of absolute concentrations.

Real-World Vehicle Emissions: A Summary of the Sixteenth Coordinating Research Council On-Road Vehicle Emissions Workshop

The Coordinating Research Council held its 16th workshop in March 2006, with 83 presentations describing the most recent mobile source-related emissions research. In this paper, we summarize the presentations from researchers who are engaged in improving our understanding of the contribution of mobile sources to air quality. Participants in the workshop discussed evaluation of inuse emissions control programs, effects of fuels on emissions, emission models and emission inventories, results from gas- and particle-phase emissions studies from spark-ignition and diesel-powered vehicles, and efforts to improve our capabilities in performing on-board emissions measurements, as well as topics for future research.

Real-World Vehicle Emissions: A Summary of the 15th Coordinating Research Council On-Road Vehicle Emissions Workshop

The Coordinating Research Council held its 15th workshop in April 2005, with nearly 90 presentations describing the most recent mobile source-related emissions research. In this paper, the authors summarize the presentations from researchers who are engaged in improving our understanding of the contribution of mobile sources to air quality. Participants in the workshop discussed emission models and emission inventories, results from gas- and particle-phase emissions studies from spark-ignition and diesel-powered vehicles (with an emphasis in this workshop on particle emissions), effects of fuels on emissions, evaluation of in-use emissions control programs, and efforts to improve our capabilities in performing on-board emissions measurements, as well as topics for future research.

Optimization-Based Source Apportionment of PM2.5 Incorporating Gas-to-Particle Ratios

A modified approach to PM2.5 source apportionment is developed, using source indicative SO2/PM2.5, CO/PM2.5, and NOx/PM2.5 ratios as constraints, in addition to the commonly used particulate-phase source profiles. Additional information from using gas-to-particle ratios assists in reducing collinearity between source profiles, a problem that often limits the source-identification capabilities and accuracy of traditional receptor models. This is especially true in the absence of speciated organic carbon measurements. In the approach presented here, the solution is based on a global optimization mechanism, minimizing the weighted error between apportioned and ambient levels of PM2.5 components, while introducing constraints on calculated source contributions that ensure that the ambient gas-phase pollutants (SO2, CO, and NOy) are reasonable. This technique was applied to a 25-month dataset of daily PM2.5 measurements (total mass and composition) at the Atlanta Jefferson Street SEARCH site. Results indicate that this technique was able to split the contributions of mobile sources (gasoline and diesel vehicles) more accurately than particulate-phase source apportionment methods. Furthermore, this technique was able to better quantify the direct contribution (primary PM2.5) of coal-fired power plants to ambient PM2.5 levels.

Real-World Vehicle Emissions: A Summary of the 14th Coordinating Research Council On-Road Vehicle Emissions Workshop

The Coordinating Research Council held its 14th Vehicle Emissions Workshop in March 2004, where results of the most recent on-road vehicle emissions research were presented. We summarize ongoing work from researchers who are engaged in improving our understanding of the contribution of mobile sources to ambient air quality and emission inventories. Participants in the workshop discussed efforts to improve mobile source emission models, light- and heavy-duty vehicle emissions measurements, on- and off-road emissions measurements, effects of fuels and lubricating oils on emissions, as well as topics for future research.

Area, mobile, and point source contributions to ground level ozone: a summer simulation across the continental USA

In this study, we assessed how much ground level O 3 originated from area, mobile, and point sources in the presence of biogenic emissions. We simulated ground level O 3 formation over a three-month period (June–August, 1995) across the continental US, using the procedure for factor separation (FS) to calculate our source contribution. The modeling system includes Sparse Matrix Operator Kernel Emissions (SMOKE), an emissions model, meteorological data from a regional climate model, and SAQM, a 3-D chemistry-transport air quality model. The FS technique is applied to quantify the pure impact from an individual source category as well as the additional impact due to the synergy among source categories. In performing this type of source contribution, it is important to note that the synergy among source categories may sometimes actually suppress O 3 formation in comparison with the sum of pure contribution from the individual source category. In such a case, a negative source contribution is assigned to this interaction. Our simulation results indicate that this suppression does occur and that pure and synergistic contributions vary over time and space. The full potential of each source category in O 3 formation (the pure contribution) is not achieved when emissions from the other source categories are accounted for, implying that control of emissions from one source category could increase the potential of emissions from another source category to produce O 3 .

A cohort‐based approach for characterizing lifetime inhalation cancer risk from time‐varying exposure to air toxics from ambient sources

AbstractIn recent years, the U.S. EPA as well as state and local agencies have released a number of risk characterizations addressing potential inhalation cancer risks from exposure to ambient sources of air toxics (e.g., U.S. EPA's 1993 Motor Vehicle‐Related Air Toxics Study, the South Coast Air Quality Management District's MATES‐II study, the U.S. EPA's National Scale Air Toxics Assessment). In these assessments, quantitative estimates of cancer risk are often presented as point estimates and/or distributions of individual upper‐bound lifetime risks. The individual upper‐bound lifetime cancer risk is the probability that an individual in a given population will contract cancer if exposed continuously to a given concentration of an airborne carcinogen over an assumed lifetime. Individual risk estimates in these studies are usually based on average or median exposures for a wide population distribution.These estimates generally assume continuous exposure over an entire lifetime to levels estimated for 1 or a few years and do not account for expected changes in exposure over time. For example, risk estimates in U.S. EPA's recent National Scale Air Toxics Assessment assume individuals will be exposed to 1996 levels over a 70‐year lifetime. However, exposures to most air toxics are expected to change over time as a result of mobile and stationary source emission control programs.In this paper, a cohort‐based approach, which estimates individual lifetime cancer risk based on time‐weighted exposure over a lifetime, is presented. This approach accounts for changes in exposure level over time, including decreases anticipated as a result of regulatory programs. It also incorporates differences in exposures to children and adults that result from certain differences in time–activity patterns, integrating them into a single value for a cohort. Moreover, this paper presents a case study applying this approach to estimate average nationwide individual cancer risks from exposure to the highway mobile source contribution to ambient benzene. The case study includes estimates for the general population and a highly exposed demographic group, outdoor workers. © 2004 American Institute of Chemical Engineers Environ Prog, 23: 120–125, 2004

Real-World Vehicle Emissions: A Summary of the Thirteenth Coordinating Research Council On-Road Vehicle Emissions Workshop

The Coordinating Research Council held its thirteenth Vehicle Emissions Workshop in April 2003, when results of the most recent on-road vehicle emissions research were presented. Ongoing work from researchers who are engaged in improving understanding of the contribution of mobile sources to ambient air quality and emission inventories is summarized here. Participants in the workshop discussed efforts to improve mobile source emission models, the role of on-board diagnostic systems in inspection and maintenance programs, light- and heavy-duty vehicle emissions measurements, on- and off-road emissions measurements, effects of fuels and lubricating oils on emissions, as well as topics for future research.

Regional Modeling of the Atmospheric Fate and Transport of Benzene and Diesel Particles

The Community Multiscale Air Quality model (CMAQ) was modified to simulate the atmospheric fate and transport of benzene and diesel particles. We simulated the July 11-15, 1995 period over a domain covering the eastern United States with a 12-km horizontal resolution and a finer (4 km) resolution over a part of the northeastern United States that includes Washington, DC and New York City. The meteorological fields were obtained from a simulation conducted earlier with the mesoscale model MM5. Gridded emission files for benzene and diesel particles were developed using the SMOKE modeling system. The results of the model simulations showed that benzene concentrations were commensurate with available measurements. Over the 4-km resolution domain, a comparison between simulated and measured 24-h average concentrations showed a fractional error of 0.46, a fractional bias of 0.14, and a coefficient of determination (r2) of 0.25. A comparison between simulated benzene hourly concentrations in New York City and in the Brigantine Wilderness Area, NJ, showed that urban concentrations were greater than the remote area concentrations by a factor of 2-5. The results of the diesel particle simulations showed spatial and temporal patterns that were similar to those obtained for benzene. However, because of the lesser contribution of on-road mobile sources to diesel particle emissions compared to benzene emissions, diesel particle concentrations showed stronger gradients between urban areas and remote areas. A comparison between diesel particle concentrations in New York City and in the Brigantine Wilderness Area, NJ, showed that the urban concentrations were greater than the remote area concentrations by a factor of 2-10. Assuming that diesel particles consist of 50% "elemental" carbon (EC), the simulated EC concentrations were in close agreement (within 10%) with the measured concentration in the urban area (Washington, DC) but were significantly lower than the measured EC concentrations in the remote area (Brigantine Wilderness Area). This result suggests that other sources beside diesel fuel engines contribute to atmospheric EC concentrations and that EC may not be a good surrogate for diesel particles. A comparison of both benzene and diesel particle simulated concentrations between an urban area (New York City) and a remote area (Brigantine Wilderness Area) shows that, at a spatial resolution of 4 km, the regional background may contribute from 10 to 20% to the peak concentrations. These results suggest that the regional background may not be negligible and should be taken into account in urban air toxics studies.