Air Toxics Exposure from Vehicle Emissions at a U.S. Border Crossing: Buffalo Peace Bridge Study

EPA Grant Number: R834677C158
Subproject: this is subproject number 158 , established and managed by the Center Director under grant R834677
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: Health Effects Institute (2010 — 2015)
Center Director: Greenbaum, Daniel S.
Title: Air Toxics Exposure from Vehicle Emissions at a U.S. Border Crossing: Buffalo Peace Bridge Study
Investigators: Spengler, John D.
Institution: Harvard T.H. Chan School of Public Health , Health Effects Institute (HEI)
EPA Project Officer: Chung, Serena
Project Period: April 1, 2010 through March 31, 2015
RFA: Health Effects Institute (2010) RFA Text |  Recipients Lists
Research Category: Health Effects , Air Quality and Air Toxics , Air


Motor vehicles and other combustion sources emit many air toxics that are either known or suspected, with sufficient exposure, to cause adverse health effects. Characterization of exposure to air toxics has been challenging, in part, because of the low ambient levels of individual compounds. Dr. John Spengler and colleagues hypothesized that vehicle-related emissions from traffic backed up at the Peace Bridge in Buffalo, New York, one of the nation’s busiest border crossings, would result in higher levels of mobile-source air toxics (MSATs) directly   downwind. They proposed a study to measure levels of air toxics, including MSATs, upwind and downwind of the plaza adjacent to the Peace Bridge, to examine the relation between traffic at the bridge and pollutant concentrations in ambient air, and to explore geographic patterns of ambient air pollutants in this potential hot spot for mobile-source emissions.


The investigators measured levels of a large number of compounds that might be expected in exhaust from diesel and gasoline vehicles, including volatile organic compounds (VOCs), polycylic aromatic hydrocarbons (PAHs), and nitrogenated PAHs (NPAHs). Their analyses focused on comparing pollutant levels measured at fixed sites on opposite sides of the 17-acre plaza adjacent to the Peace Bridge, which comprised the U.S. Customs Building, a customs inspection and holding area, tollbooths, a duty-free store, the Peace Bridge Authority Administration Building, and parking space. Residential and commercial areas abut the plaza to the east, north, and south, with Lake Erie and the Niagara River to the west.

Investigators sampled air at sites upwind and downwind of the plaza and tested a variety of routes for mobile monitoring in a neighborhood next to the plaza. They collected meteorologic data and bridge traffic counts by vehicle type (cars, trucks, and buses), for all sampling days. Prevailing wind directions were determined from 10 years of weather data from the Buffalo Niagara International Airport, which demonstrated that the wind blows from the west side of the plaza (off Lake Erie) about 45% of the time (lake winds) and from the east on the Buffalo side of the plaza (city winds) about 31% of the time. The investigators established two fixed sampling sites for both continuous monitoring and integrated sampling during the pilot study: one to the southwest of the plaza at the Great Lakes Center (GLC site), which they describe as an upwind site, and the other in front of the Episcopal Church Home (Chapel site) adjacent to the east side of the plaza, which they describe as a downwind site. They also tested routes, equipment, and protocols for mobile monitoring of pollutants around the Peace Bridge plaza area, including the neighborhood of Buffalo directly to the east. The researchers added a third fixed sampling site in this neighborhood (School site) during the winter pilot program.

After the two pilot studies, Spengler’s team conducted two larger-scale sampling campaigns featuring both fixed-site and mobile monitoring components. Samples were collected simultaneously at all three fixed sampling sites for two weeks in July and two weeks in January. The research team collected integrated samples at these sites and also from collocated real-time continuous monitors that took measurements every minute. The mobile monitoring campaign was designed to assess the levels of selected pollutants in the neighborhood adjacent to the Peace Bridge plaza. Staff members wore backpacks containing air monitoring equipment and carried GPS (Global Positioning System) units while walking along one of four designated routes in the neighborhood. Pollutant data and GPS coordinates from the mobile monitoring campaigns were used to create maps showing the spatial distribution of pollutants in the neighborhood east of the Peace Bridge plaza.

Expected Results:

The investigators compiled a wealth of comparative data on several different classes of MSATs — VOCs and carbonyls, elements, PAHs, and NPAHs — and measurements from continuous sampling of particulate matter (PM) ≤ 10 μm and ≤ 2.5 μm in aerodynamic diameter (PM10 and PM2.5, respectively), ultrafine particles (UFPs, defined as particles < 0.1 μm in aerodynamic diameter), particle-bound PAHs (pPAHs), and gaseous pollutants. For PM10 and PM2.5 , and for the fraction of elemental carbon (EC)  present in the collected PM2.5 , the mean daytime levels were highest at the Chapel site (typically downwind of the plaza), and higher at the residential School site than at the upwind GLC site.

The investigators created summary categories for selected VOCs and chlorinated compounds. In weekday 12-hour samples, overall mean and median levels of benzene, toluene, ethylbenzene, and xylenes (BTEX) were highest at the neighborhood School site, followed by the Chapel site, and then the GLC site. Overall mean and median levels of a summary category of five chlorinated compounds were very similar across the three sites. Median daytime benzene and formaldehyde levels were lowest by far at the GLC site. Overall mean and median daytime acetaldehyde levels were highest at the GLC site, nearly as high at the School site, and much lower at the Chapel site. Acetone levels for all daytime samples were slightly elevated at the GLC site.

Spengler’s team analyzed fixed-site PM 2.5 samples for 28 different elements, of which only six —calcium, chromium, manganese, iron, copper, and antimony — varied considerably across the three fixed sampling sites. Mean daytime weekday levels of these were, on average, higher at the Chapel site than at the other sites. The authors suggest that the higher concentrations of these elements at the Chapel site were related to emissions from traffic at the Peace Bridge plaza.

The researchers also noted important contrasts in levels of PAHs and NPAHs across the three fixed sampling sites. Concentrations of all but a few of the PAH compounds were higher at the Chapel site when the site was downwind of the city of Buffalo (rather than downwind of the bridge), implying that regional combustion and urban infrastructure contributed more PAHs than the emissions from traffic at the Peace Bridge plaza. Low-molecular-weight PAHs, however, were consistently highest at the Chapel and School sites. Comparison of median concentrations of 14 NPAHs at the GLC and Chapel sites under lake-wind conditions showed that some were notably higher at the downwind Chapel site, indicating that traffic at the Peace Bridge plaza was a potential local source for these compounds.

The authors performed a source apportionment analysis using principal component analysis to analyze the data for individual elements and positive matrix factorization for the site-specific PAH measurements from the winter and summer sampling campaigns. The principal component analysis indicated that measured levels of elements associated with traffic emissions were higher at the Chapel site when it was downwind of the Peace Bridge plaza. Positive matrix factorization analyses, which divided the PAHs into light, medium, and heavy profiles based on their molecular weight, demonstrated relatively higher levels of the light PAHs at the upwind GLC site, higher levels of the medium PAHs at the downwind Chapel and School sites, and relatively uniform distribution of the heavy PAHs at all three sites.

Overall, to assess the plausibility of a relationship between traffic at the Peace Bridge plaza and levels of airborne pollutants at the Chapel and GLC sites on either side of the plaza, Spengler’s team compared measurement data obtained with lake winds and with winds blowing over the city of Buffalo toward the lake. Pairing samples by sampling period and calculating the ratio of measured levels at the Chapel site to those at the GLC site, the authors ranked the results in terms of EC reflectance (EC-r). The Chapel-to-GLC ratios for EC-r were highest with lake-wind events, which would enrich levels of EC-r at the downwind Chapel site if they were the result of mobile-source emissions at the plaza. Based on these comparisons and their overall results, the investigators suggest that the traffic at the plaza was a source for the higher levels of compounds measured at the Chapel site.

Supplemental Keywords:

Health Effects, Air Toxics, VOCs,  PAHs, epidemiology, carcinogens, aldehyde, air toxics, mist chamber methodology, carbonyls, ambient air sampling, BTEX, benzene, particulate matter, mobile-source emissions, motor vehicle exhaust

Relevant Websites: Exit

Main Center Abstract and Reports:

R834677    Health Effects Institute (2010 — 2015)

Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
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