Coupling quasi-spectral microphysics with multiphase chemistry: a case study of a polluted air mass at the top of the Puy de Dome mountain (France)

An explicit multiphase chemistry model (Atm. Environ. 34 (29/30) (2000) 501 5) has been coupled with quasi-spectral microphysics, based upon Berry and Reinhardt's parameterizations (1974a, b). This coupled model has been initi alized with polluted conditions as observed at the Puy de Dome mountain in the center of France and for a maritime cloud. The presence of clouds results in two effects on multiphase chemistry: a di rect effect through mass transfer, solubility and reactivity, and an indire ct effect through microphysical transfer from cloud water into rainwater an d redistribution of reactive soluble species among interstitial air, cloud droplets and raindrops. Results demonstrate that microphysical processes are necessary to sketch ou t the complex, nonlinear multiphase chemistry in a real cloud. In addition to the direct exchange through mass transfer, incorporation of reactive oxi dants such as HOx in droplets can arise and consequently make those species no longer available for reacting in the gas-phase. Moreover, microphysical coalescence conversions favor NO., destruction and enhance the chemical ni tric acid production. Coalescence of cloud drops to form rain transfers dis solved species into drops that are undersaturated compared to Henry's law e quilibrium. The rain becomes a reservoir for these species, allowing aqueou s chemistry to produce more nitric acid than would be possible without them presence of rain. Finally, for the different cloud types, the fate of those intermediate and reactive species is investigated, looking at their budget in clear sky situ ation versus cloudy and/or rainy situations. (C) 2001 Elsevier Science Ltd. All rights reserved.