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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D20307, doi:10.1029/2005JD006172, 2006

Anthropogenic emissions of nonmethane hydrocarbons in the northeastern United States: Measured seasonal variations from 1992–1996 and 1999–2001

Ben H. Lee

Department of Environmental Science, Policy and Management, University of California, Berkeley, California, USA

J. William Munger

Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA

Steven C. Wofsy

Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA

Allen H. Goldstein

Department of Environmental Science, Policy and Management, University of California, Berkeley, California, USA

Abstract

Harvard Forest, a rural site located in central Massachusetts downwind of major urban-industrial centers, provides an excellent location to observe a typical regional mixture of anthropogenic trace gases. Air that arrives at Harvard Forest from the southwest is affected by emissions from the U.S. east coast urban corridor and may have residual influence from emissions in the upper Ohio Valley and Great Lakes region farther to the west. Because of its relatively long distance from large individual emission sources, pollution plumes reaching the site are a homogenized mixture of regional anthropogenic emissions. Concentrations of C₂-C₆ hydrocarbons along with CO and NO_y were measured nearly continuously from August 1992 through July 1996 and from June 1999 through November 2001. By correlating observed concentrations to acetylene, which is almost solely produced during combustion, we are able to detect seasonal trends in relative emissions for this series of trace gases. Seasonal changes in n-butane and i-butane emissions may largely be influenced by different gasoline formulations in late spring and summer. Shifts in evaporation rates due to the annual temperature cycle could induce a seasonal pattern for n-pentane, i-pentane and n-hexane emissions. Emissions of ethane and propane lack clear seasonality relative to acetylene emissions and also correlate less with acetylene than other gases, indicating that emissions of these two gases are strongly influenced by sources not associated with fuel combustion. Changes in the observed correlations of CO₂ and CO relative to acetylene are consistent with published changes in the estimated emissions of CO₂ and CO over the past decade, though variability in the observations makes it difficult to precisely quantify these changes.

Received 4 May 2005; accepted 5 July 2006; published 21 October 2006.

Index Terms: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry.

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Citation: Lee, B. H., J. W. Munger, S. C. Wofsy, and A. H. Goldstein (2006), Anthropogenic emissions of nonmethane hydrocarbons in the northeastern United States: Measured seasonal variations from 1992–1996 and 1999–2001, J. Geophys. Res., 111, D20307, doi:10.1029/2005JD006172.

Copyright 2006 by the American Geophysical Union.