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Regional Analysis of Nonmethane Volatile Organic Compounds in the Lower Troposphere of the Southeast
 

Summary: Regional Analysis of Nonmethane Volatile Organic
Compounds in the Lower Troposphere of the Southeast
United States
Mita Das1
and Viney P. Aneja2
Abstract: Nonmethane organic compounds NMOCs along with ozone as well as other trace gas and meteorological parameters were
measured at eight rural sites located in the Southeast United States, as part of the Southern Oxidants Study. Fifty-four C2 C10 NMOCs
were collected from 1,2001,300 local time, once every six days from September 1992 through October 1993 and intermittently during
1994. This study was undertaken to characterize the nonmethane hydrocarbons in the rural areas of Southeast United States with respect
to their concentrations, reactivities, and relative importance of natural and anthropogenic abundances of NMOCs. Though the sites are
well removed from large urban source regions, the observations show a clear anthropogenic influence on the hydrocarbon levels at these
rural sites. The data for the sites show similar seasonal patterns for total NMOC with summer maxima average concentrations of 198
ppbC at the Long Creek, South Carolina, site to 47 ppbC at the Candor, North Carolina site and fall minima average concentrations of
73 ppbC at the Long Creek site to 31 ppbC at the Centreville, Alabama site . A secondary maximum is observed during the winter. A
seasonal trend was observed in the concentrations of light molecular weight C2 C4 NMOCs ethane, ethene, acetylene, propane, i-butane,
and n-butane with a winter maximum and a summer minimum. An analysis of changes in C2 C4 hydrocarbon ratios over a period of one
year indicates that the variation is most likely due to seasonal changes in OH concentrations. A seasonal trend was also observed for the
biogenically emitted NMOC, isoprene, with summer maxima average concentrations of 37 ppbC at the Long Creek, South Carolina, site
to 8.6 ppbC at the Giles County, Tennessee and Metter, Georgia, sites and winter minima with winter seasonal values below the level of
detection. Isoprene was observed to be the most dominant NMOC at most sites during the summer. The ambient concentrations of

  

Source: Aneja, Viney P. - Department of Marine, Earth and Atmospheric Sciences, North Carolina State University

 

Collections: Environmental Sciences and Ecology; Geosciences