INFLUENCE OF AIR-MASS HISTORY ON BLACK CARBON CONCENTRATIONS AND REGIONAL CLIMATE FORCING IN SOUTHEASTERN UNITED-STATES

Atmospheric black carbon (BC) mass concentrations in the southeastern United States have been measured at a regionally representative site n ear Mount Mitchell, North Carolina (35 degrees 44'05''N, 82 degrees 17 '15''W, 2038 m elevation), the highest peak in the eastern United Stat es, during a 9 month period from June to October 1996 and March to Jun e 1997. BC concentrations are measured by an aethalometer, which opera tes by measuring the attenuation of light through a sample. All measur ed BC concentrations are reported in terms of air mass histories deter mined from back trajectory analysis using the Hybrid Single-Particle L agrangian Integrated Trajectory (HY-SPLIT) model. Air masses influenci ng the site have been classified as polluted, marine, and continental according to SOx and NOx emission inventories. The average BC mass con centrations for each sector are 216.6 +/- 47.8 ng m(-3) for polluted a ir masses, 65.6 +/- 23.5 ng m(-3) for marine air masses, and 169.9 +/- 50.6 ng m(-3) for continental air masses. A positive relationship bet ween cloud condensation nuclei and BC concentrations suggest at times the BC measured at the site may be internally mixed. The average BC co ncentration found in cloud water is 74.2 mu g kg(-1). Derived BC to su lfate mass ratios ranged from 0.01 to 0.06.