In this paper we present simulations of the effect of nitric acid (HNO<sub>3</sub>) on cloud processing of aerosol particles. Sulfuric acid (H<sub>2</sub>SO<sub>4</sub>) 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 HNO<sub>3</sub> affects the H<sub>2</sub>SO<sub>4</sub> 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.