Characteristics of water-soluble components of atmospheric aerosols in Yokohama and Mt. Oyama, Japan from 1990 to 2001

We continuously collected aerosol samples of PM7 from 1990 to 1997 and of PM10–2 and PM2 from 1998 to 2001 and measured their water-soluble components of pH, conductivity, major ions, dissolved organic carbon (DOC) and total mass (TM) in an urban site, Yokohama (35°28′N, 139°38′E) and the mountainside (680 m asl) of Mt. Oyama (35°28′N, 139°46′E, 1252 m asl), Japan, to contrast the aerosol composition between an urban site and a mountain site. In Yokohama, annual mean TM concentration decreased gradually for over 10 years with the decrease of NH4+, Mg2+, Cl−, and SO42− concentrations, and TM concentrations were the highest in winter and the lowest in summer. At Mt. Oyama, there was no significant change in the duration, and TM concentrations were the highest from late spring to early summer, although the seasonal variation was smaller. Equivalent concentration ratio of Cl− to Na+ at Mt. Oyama was lower than that in Yokohama, because Cl loss which occurred was larger for the aerosol collected at Mt. Oyama remote from the sea rather than Yokohama. The conversion ratio of sulfur to sulfate was calculated and the ratio was not affected strongly by the variation of Ox concentration at both sites and was high at Mt. Oyama in summer. NH4+, NO3−, SO42−, and DOC concentrations were higher under weak wind velocity than those under strong wind velocity regardless of the wind direction in both the sites.