Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 6 6 2006 10.5194/acp-6-1627-2006 http://www.atmos-chem-phys.net/6/1627/2006/ http://www.atmos-chem-phys.net/6/1627/2006/acp-6-1627-2006.html http://www.atmos-chem-phys.net/6/1627/2006/acp-6-1627-2006.pdf 1627 1634 2006-05-19 The influence of nitric acid on the cloud processing of aerosol particles S. Romakkaniemi H. Kokkola K. E. J. Lehtinen A. Laaksonen Department of Applied Physics, University of Kuopio, P.O. BOX 1627, FIN-70211 Kuopio, Finland University of Kuopio and Finnish Meteorological Institute, Department of Applied Physics, P.O. BOX 1627, FIN-70211 Kuopio, Finland now at: School of Earth, Atmospheric and Environmental Sciences, University of Manchester, P.O. BOX 88, Manchester M60 1QD, UK In this paper we present simulations of the effect of nitric acid (HNO₃) on cloud processing of aerosol particles. Sulfuric acid (H₂SO₄) production and incloud coagulation are both affected by condensed nitric acid as nitric acid increases the number of cloud droplets, which will lead to smaller mean size and higher total surface area of droplets. As a result of increased cloud droplet number concentration (CDNC), the incloud coagulation rate is enhanced by a factor of 1–1.3, so that the number of interstitial particles reduces faster. In addition, sulfuric acid production occurs in smaller particles and so the cloud processed aerosol size distribution is dependent on the HNO₃ concentration. This affects both radiative properties of aerosol particles and the formation of cloud droplets during a sequence of cloud formation-evaporation events. It is shown that although the condensation of HNO₃ increases the number of cloud droplets during the single updraft, it is possible that presence of HNO₃ can actually decrease the cloud droplet number concentration after several cloud cycles when also H₂SO₄ production is taken into account.