Chemical forms and sources of extremely high nitrate and chloride in winter aerosol pollution in the Kanto Plain of Japan

The spatial distributions, chemical forms, and potential sources have been investigated for extremely high concentrations of Cl- and NO-3 in aerosols collected during an extensive study for winter pollution episodes in the Kanto Plain of Japan. Air monitoring are conducted at 10 sites including the rooftops of skyscrapers during two measurement periods in November–December 1991. Similarity in the diurnal variation patterns of NO-3 among the sampling sites suggests that its precursor HNO3 is formed by reactions in the atmosphere, while difference in the maximum concentration of Cl- between the sites indicates the presence of local sources. Measurements at ground level and on the rooftops of skyscrapers show that the pronounced diurnal variations of both components are phenomena occurring in the layer extending from the ground surface to at least 200 m height. Intensified measurements at two ground sites indicate that (1) NO-3 and non sea-salt Cl- are predominantly in the fine mode, (2) [NO-3] + [Cl-] and [NH+4] are in equivalence, (3) gaseous HCl, HNO3, and NH3 are in equilibrium with particulate NH4Cl and NH4NO3. From these results, it is concluded that measured Cl- and NO-3 are predominantly in the form of NH4Cl and NH4NO3, respectively. The behavior of peroxyacetyl nitrate (PAN) indicates that HNO3, the precursor of NO-3, is produced in the photochemical reactions of the NOx-hydrocarbons system. The elevated concentration of NO2 measured simultaneously in the pollution episodes is regarded as an alternative form of O3 produced in photochemical reactions. As the precursor of Cl- in aerosols, sources of HCl are discussed, and the emission from incineration of domestic and industrial waste in the area is estimated.