Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 5 2005 10.5194/acpd-5-10197-2005 http://www.atmos-chem-phys-discuss.net/5/10197/2005/ http://www.atmos-chem-phys-discuss.net/5/10197/2005/acpd-5-10197-2005.html http://www.atmos-chem-phys-discuss.net/5/10197/2005/acpd-5-10197-2005.pdf 10197 10216 2005-10-20 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 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. Increased acidity due to HNO₃ affects the H₂SO₄ production. As a result of increased cloud droplet number concentration (CDNC), the incloud coagulation rate is enhanced, so that the number of interstitial particles reduces faster. In addition, sulfuric acid production occurs in smaller particles and this will lead to higher number of particles in the accumulation mode.