Chemistry and Deposition of Soot Particles in Moist Air and Fog

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Abstract
From numerous laboratory experiments it is well known that gaseous compounds are absorbed and can be oxidized on aerosol particles and in droplets by different processes. But only few studies have been performed in the atmosphere that show the contribution of heterogeneous reactions to sulfate and nitrate formation processes. Therefore vertically resolved and time-dependent measurements of chemical compounds and meteorological quantities were conducted near a polluted area to study the formation of reaction products on soots and other particles and the activation of these particles during fog formation. Furthermore, the influence of these particles on chemical reactions inside fog droplets was examined. The fluxes of different compounds, particles, and droplets were calculated from vertical profiles of chemical, physical, and meteorological quantities. If the horizontal and vertical transport from the source region to the measuring site is considered, the observed particle composition can be calculated based on reaction laws from laboratory experiments. The influence of relative humidity on the reaction rate was found to be especially important in the atmosphere. Soot particles are often found to be activated to a lower extent than other particles during fog formation. Then the deposition fluxes of soots in humid air and fog are smaller than for other particles.