CARBON AEROSOLS AND ATMOSPHERIC PHOTOCHEMISTRY

Carbon aerosols are produced by all combustion processes. This paper i nvestigates some possible effects of heterogeneous reduction of atmosp heric constituents on carbon aerosols. Reduction of HNO3, NO2, and O-3 on carbon aerosols may be an important effect of increased air traffi c that has not been considered to date. It is shown that if HNO3, NO2 and O-3 are heterogeneously reduced on atmospheric amorphous carbon ae rosols, then a significant, lower stratospheric ozone loss mechanism c ould exist. This ozone loss mechanism is almost independent of tempera ture and does not require the presence of sunlight. The mechanism can operate at all latitudes where amorphous carbon aerosols are present. The relative importance of the mechanism increases with nightlength. T he reduction of HNO3 on carbon aerosols could also be a significant re noxification process wherever carbon aerosols are present. Owing to th e very different soot levels in the two hemispheres, this implies that there should be a hemispheric assymetry in the role of these mechanis ms. The renoxification leads to simulated tropospheric HNO3/NOx ratios that are close to those Observed. In contrast ta the stratospheric re sponse, the tropospheric production of NOx due to the reduction of HNO 3 would lead to tropospheric ozone production.