Particulate Carbon at Various Locations in the United States

Abstract

Particulate elemental and organic carbon concentrations were determined on filters collected between 1972 and 1980 at ten United States’ sites representing urban, suburban, rural, and remote areas. The results showed that particulate elemental carbon is ubiquitous with mean concentrations ranging from 1.1 micrograms per cubic meter at the remote site in South Dakota to 13.3 micrograms per cubic meter in a congested area in New York City. About 80% of the elemental carbon mass consists of particles with a diameter of less than 2.5 micrometers. Particulates in this size range are responsible for most pollutant-related visibility reductions. Since it appears that elemental carbon is the only light-absorbing particulate species, the specific light-absorption coefficient for elemental carbon was calculated to be 12.7 m2/g while the specific light-scattering coefficient was 3.2 m2/g. Using these coefficients, the contributions of elemental carbon to the observed visibility reduction at the various sites are estimated. These range from 6 to 38%. Also discussed are the seasonal and diurnal variations of particulate elemental and organic carbon as well as the contribution from secondary organic particulates. In addition, an updated carbon-source apportionment, based on recent analytical developments, is presented for the Denver area.