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Partitioning of HNO 3 and particulate nitrate over Tokyo: Effect of vertical mixing

2006; American Geophysical Union; Volume: 111; Issue: D15 Linguagem: Inglês

10.1029/2005jd006887

2156-2202

Yu Morino, Y. Kondo, N. Takegawa, Yuzo Miyazaki, Kazuyuki Kita, Y. Komazaki, Masato Fukuda, Takuma Miyakawa, Nobuhiro Moteki, Douglas R. Worsnop,

Atmospheric and Environmental Gas Dynamics

Ground‐based measurements of gas‐phase nitric acid (HNO 3 ) and particulate nitrate (NO 3 − ) were performed in Tokyo during 2003–2004. These measurements provide a comprehensive data set for investigating the diurnal and seasonal variations of gas‐phase HNO 3 and particulate NO 3 − and the thermodynamic equilibrium of these compounds. HNO 3 and NO 3 − have distinct diurnal and seasonal variations, especially in summer. This study shows that the thermodynamic equilibrium of HNO 3 and NO 3 − and the production rate of total nitrate (TNO 3 = HNO 3 + NO 3 − ) are the major controlling factors affecting these seasonal and diurnal variations. A thermodynamic equilibrium model (ISORROPIA) is newly coupled with a one‐dimensional (1‐D) model to take into account the effect of vertical mixing during daytime on the partitioning of HNO 3 and NO 3 − by constraining the TNO 3 concentrations to the observations. The 1‐D model reproduces the NO 3 − /TNO 3 ratios observed during daytime, whereas the equilibrium model significantly underestimates these ratios. The agreement between the observed and calculated NO 3 − /TNO 3 ratios is improved over the observed temperature range (1°–34°C) and relative humidity (18–95%) by the 1‐D model. These results suggest the importance of vertical mixing in determining HNO 3 ‐NO 3 − partitioning in the boundary layer. It is also found that the mass accommodation coefficient for HNO 3 needs to be approximately 0.1 to explain the observed HNO 3 ‐NO 3 − partitioning at the surface.