LATITUDINAL DISTRIBUTION OF BLACK CARBON SOOT IN THE UPPER TROPOSPHERE AND LOWER STRATOSPHERE

Black carbon soot from the upper troposphere and lower stratosphere ha s been systematically collected at latitudes from 90 degrees N to 45 d egrees S. The measured latitudinal distribution of this soot at 10- to 11-km altitude is found to covary with commercial air traffic fuel us e, suggesting that aircraft fuel combustion at altitude is the princip al source. In addition, at latitudes where the commercial air traffic is high, measured black carbon soot values are high even at 20-km alti tude, suggesting that aircraft-generated soot injected just above the tropopause may be transported to higher altitudes. During the volcanic ally influenced period in which these samples were collected, the numb er abundances, total mass, and calculated total surface area of black carbon soot are 2-3 orders of magnitude lower than similar measures of sulfuric acid aerosol. During volcanically quiescent periods, the cal culated total surface area of black carbon soot aerosol is of the same order of magnitude as that of the background sulfuric acid aerosol. I t appears from this comparison that black carbon soot is only capable of influencing lower stratosphere or upper troposphere chemistry durin g periods when the aerosol budget is not dominated by volcanic activit y. It remains to determine the extent to which black carbon soot parti cles act as nuclei for sulfuric acid aerosol formation. However, mass balance calculations suggest that aircraft soot injected at altitude d oes not represent a significant source of condensation nuclei for sulf uric acid aerosols.