Behaviors of volatile inorganic components in urban aerosols

A multicomponent gas–aerosol equilibrium model (Kim et al., 1993a,b; Kim and Seinfeld, 1995) was used to explain the behaviors of water content and other volatile species in the aerosols observed in polluted air mass in Central Japan. It was found that gas–aerosol equilibrium was attained after long-range transport of polluted air mass (e.g., 50 km) from emission source area, while it was not completed in large emission source areas. The present model predicted with high accuracy the gas–aerosol equilibrium of ammonium, nitrate and chloride at remote sites. The correlation coefficient was R=0.98 for ammonia and more than R=0.86 for gaseous nitric acid. It was R=0.94 for gaseous hydrochloric acid, which meant significant chlorine deficit under high-temperature and low humidity conditions was also predicted accurately. The predicted water content was consistent with that calculated by the semi-theoretical Winklerʹs formula (Aerosol Sceince, 13, 1973, 373–387). At RH=90% the water content attained almost the same weight as that of dry aerosol, while at about RH=60% it was less than 10%. In contrast, temperature dependency of the water content was weak except for very high air temperature conditions in summer. Finally, it emphasized the superiority of the multicomponent approach for gas–aerosol equilibrium, compared with the binary-component approach.