Concentrations of mobile source air pollutants in urban microenvironments

Abstract

Human exposures to criteria and hazardous air pollutants (HAPs) in urban areas vary greatly due to temporal-spatial variations in emissions, changing meteorology, varying proximity to sources, as well as due to building, vehicle, and other environmental characteristics that influence the amounts of ambient pollutants that penetrate or infiltrate into these microenvironments. Consequently, the exposure estimates derived from central-site ambient measurements are uncertain and tend to underestimate actual exposures. The Exposure Classification Project (ECP) was conducted to measure pollutant concentrations for common urban microenvironments (MEs) for use in evaluating the results of regulatory human exposure models. Nearly 500 sets of measurements were made in three Los Angeles County communities during fall 2008, winter 2009, and summer 2009. MEs included in-vehicle, near-road, outdoor, and indoor locations accessible to the general public. Contemporaneous 1- to 15-min average personal breathing zone concentrations of carbon monoxide (CO), carbon dioxide (CO₂), volatile organic compounds (VOCs), nitric oxide (NO), nitrogen oxides (NO_x), particulate matter (<2.5 μm diameter; PM_2.5) mass, ultrafine particle (UFP; <100 nm diameter) number, black carbon (BC), speciated HAPs (e.g., benzene, toluene, ethylbenzene, xylenes [BTEX], 1,3-butadiene), and ozone (O₃) were measured continuously. In-vehicle and inside/outside measurements were made in various passenger vehicle types and in public buildings to estimate penetration or infiltration factors. A large fraction of the observed pollutant concentrations for on-road MEs, especially near diesel trucks, was unrelated to ambient measurements at nearby monitors. Comparisons of ME concentrations estimated using the median ME/ambient ratio versus regression slopes and intercepts indicate that the regression approach may be more accurate for on-road MEs. Ranges in the ME/ambient ratios among ME categories were generally greater than differences among the three communities for the same ME category, suggesting that the ME proximity factors may be more broadly applicable to urban MEs.

Implications:

Estimates of population exposure to air pollutants extrapolated from ambient measurements at ambient fixed site monitors or exposure surrogates are prone to uncertainty. This study measured concentrations of mobile source air toxics (MSAT) and related criteria pollutants within in-vehicle, outdoor near-road, and indoor urban MEs to provide multipollutant ME measurements that can be used to calibrate regulatory exposure models.

Acknowledgment

The authors wish to acknowledge the following DRI personnel for their assistance: Dr. Barbara Zielinska, Anna Cunningham and Mark McDaniel for organic analysis, and Dr. Judith Chow, Steven Kohl, Ed Hackett, and Brenda Cristani for analysis of inorganic species. We also gratefully acknowledge the South Coast Air Quality Management District for providing air quality monitoring data.

Funding

This study was funded by the American Petroleum Institute.

Supplemental Material

Supplemental data for this article can be accessed on the publisher’s website.http://www.tandfonline.com/uawm

Additional information

Notes on contributors

Eric M. Fujita

Eric M. Fujita is a research professor emeritus and David E. Campbell is an associate research scientist in the Division of Atmospheric Sciences at the Desert Research Institute (Nevada System of Higher Education).

W. Patrick Arnott

W. Patrick Arnott is an associate professor in the Department of Physics at the University of Nevada, Reno.

Ted Johnson

Ted Johnson is the Research Director of TRJ Environmental, Inc. in Chapel Hill, North Carolina.

Will Ollison

Will Ollison is a senior scientific advisor in the Regulatory and Scientific Affairs Department of the American Petroleum Institute in Washington, DC.