Formation and dissociation of atmospheric particulate nitrate and chloride: An approach based on phase equilibrium

Abstract

In order to evaluate the factors which may affect the phase changes of the atmospheric particulate nitrate and chloride, and to discuss the atmospheric behavior of these constituents, simultaneous measurements of atmospheric gases (HN0 3, HCl, NH 3), aerosols (N0 3 −, Cl −, NH 4 +, SO 4 2−), and associated species were conducted in Nagoya City, Japan. The temperature dependence of the phase changes of the particulate nitrate and chloride were reconfirmed. Moreover, the effects of the chemical composition of the aerosols and gases on the phase changes were also found. The formation of the fine mode nitrate and chloride was dependent on the amount of the precursors which could potentially generate particulate ammonium nitrate and chloride, respectively. This was obviously true when the potential precursors were abundant enough to allow for the homogeneous formation of the particulate ammonium nitrate and chloride, since homogeneous reactions may dominate the formation process of the fine mode nitrate and chloride. On the other hand, when the amount of the potential precursors was so sparse that the homogeneous formation was unlikely to occur, the formation of the fine mode nitrate and chloride was not dependent on the amount of the precursors. For this case, the fine mode nitrate and chloride could be produced by, probably, heterogeneous reactions on the existing particles. In the present study, it was determined that, other than the temperature, the chemical composition of the aerosols and gases-the amount of potential precursors for particulate ammonium nitrate and chloride—was an important factor to be discussed in the phase changes of the particulate nitrate and chloride.