Measurements of nonmethane hydrocarbons in 28 United States cities

Angela K Baker,Andreas J Beyersdorf,Lambert A Doezema,Aaron Katzenstein,Simone Meinardi,Isobel J Simpson,Donald R Blake,F Sherwood Rowland

doi:10.1016/j.atmosenv.2007.09.007

Abstract

Between 1999 and 2005 a sampling campaign was conducted to identify and quantify the major species of atmospheric nonmethane hydrocarbons (NMHCs) in United States cities. Whole air canister samples were collected in 28 cities and analyzed for methane, carbon monoxide (CO) and NMHCs. Ambient mixing ratios exhibited high inter- and intra-city variability, often having standard deviations in excess of 50% of the mean value. For this reason, ratios of individual NMHC to CO, a combustion tracer, were examined to facilitate comparison between cities. Ratios were taken from correlation plots between the species of interest and CO, and most NMHCs were found to have correlation coefficients ( r 2) greater than 0.6, particularly ethene, ethyne and benzene, highlighting the influence of vehicular emissions on NMHC mixing ratios. Notable exceptions were the short-chain alkanes, which generally had poor correlations with CO. Ratios of NMHC vs. CO were also used to identify those cities with unique NMHC sources.

Highlights

Nonmethane hydrocarbons (NMHCs), a class of volatile organic compounds (VOCs), are an important component of urban air pollution because of their role in the formation of tropospheric ozone (O3) and, in the case of aromatic nonmethane hydrocarbons (NMHCs), the formation of secondary organic aerosols
Transportation-related emissions normally constitute a large fraction of NMHC sources (Fujita et al, 1995; Colvile et al, 2001)
Biogenic emissions are the major known source of isoprene (Khalil and Rasmussen, 1992; Jobson et al, 1994), and the summertime sampling period lends itself to high mixing ratios of isoprene in cities with more vegetation. In those cities with significant biogenic emissions and relatively low vehicular emissions, the relatively fast reaction rates of isoprene and other biogenic species can make their contribution to ozone formation substantially greater than in other cities with large transportation sources

Summary

Introduction

Nonmethane hydrocarbons (NMHCs), a class of volatile organic compounds (VOCs), are an important component of urban air pollution because of their role in the formation of tropospheric ozone (O3) and, in the case of aromatic NMHCs, the formation of secondary organic aerosols Biogenic emissions are the major known source of isoprene (Khalil and Rasmussen, 1992; Jobson et al, 1994), and the summertime sampling period lends itself to high mixing ratios of isoprene in cities with more vegetation. In those cities with significant biogenic emissions and relatively low vehicular emissions, the relatively fast reaction rates of isoprene and other biogenic species can make their contribution to ozone formation substantially greater than in other cities with large transportation sources. While not the most abundant species, their fast reaction rates with OH make their contribution to ozone formation very significant

Methods

Results

Conclusion