Carbon aerosols and atmospheric photochemistry

Carbon aerosols are produced by all combustion processes. This paper investigates some possible effects of heterogeneous reduction of atmospheric constituents on carbon aerosols. Reduction of HNO3, NO2, and O3 on carbon aerosols may be an important effect of increased air traffic that has not been considered to date. It is shown that if HNO3, NO2 and O3 are heterogeneously reduced on atmospheric amorphous carbon aerosols, then a significant, lower stratospheric ozone loss mechanism could exist. This ozone loss mechanism is almost independent of temperature 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. The reduction of HNO3 on carbon aerosols could also be a significant renoxification process wherever carbon aerosols are present. Owing to the very different soot levels in the two hemispheres, this implies that there should be a hemispheric assymetry in the role of these mechanisms. The renoxification leads to simulated tropospheric HNO3/NOx ratios that are close to those observed. In contrast to the stratospheric response, the tropospheric production of NOx due to the reduction of HNO3 would lead to tropospheric ozone production.