The Interaction of Ozone with Soot

Introduction Atmospheric soot concentrations range from 0.5 ng m in the stratosphere up to 20 μg m in polluted urban atmospheres. Due to its irregular agglomerate structure soot aerosol offers a large surface area for interactions with reactive trace gases like ozone. Recent model results indicated that ozone concentrations in the stratosphere and upper troposphere (Lary et al, 1997; Bekki, 1997) may be affected by direct ozone loss on soot particles. However, these model predictions are uncertain because they rely on reaction probabilities which were measured on short time scales (seconds to minutes) on bulk soot samples, thus being not directly comparable to atmospheric conditions. Soot gives rise to positive climate forcing because it is a strong absorber, but a poor scatterer of solar radiation. For quantitative calculations the single scattering albedo of soot must be known. Since the physico-chemical properties of airborne soot particles change with time, their optical properties may also be time-dependent. Finally, soot particles may be volatilised as CO and/or CO2 by reaction with ozone.