PM2.5-10, PM2.5 and associated water-soluble inorganic species at a coastal urban site in the metropolitan region of Rio de Janeiro

The concentrations Of PM2.5-10, PM2.5 and associated water-soluble inorganic species (WSIS) were determined in a coastal site of the metropolitan region of Rio de Janeiro, Southeastern Brazil, from October 1998 to September 1999 (n = 50). Samples were dissolved in water and analyzed for major inorganic ions. The mean (+/- standard deviation; median) concentrations of PM2.5-10 and PM2.5 were, respectively, 26 (+/- 16; 21) mu g m(-3) and 17 (+/- 13; 14) mu g m(-3). Their mean concentrations were 1.7-1.8 times higher in dry season (May-October) than in rainy season (November-April). The WSIS comprised, respectively, 34% and 28% of the PM2.5-10 and PM2.5 masses. Chloride, Na+ and Mg2+ were the predominant ions in PM2.5-10, indicating a significant influence of sea-salt aerosols. In PM2.5,SO42- (similar to 97% nss-SO42-) and NH4+ were the most abundant ions and their equivalent concentration ratio (SO42-/NH4+ similar to 1.0) suggests that they were present as (NH4)(2)SO4 particles. The mean concentration of (NH4)(2)SO4 was 3.4 mu g m(-3). The mean equivalent PM2.5 NO3- concentration was eight times smaller than those SO42- and NH4+. The PM2.5 NO3- concentration in dry season was three times higher than in rainy season, probably due to reaction of NaCl (sea salt) with HNO3 as a result of higher levels of NOy during the dry season and/or reduced volatilization of NH4NO3 due to lower wintertime temperature. Chloride depletion was observed in both size ranges, although more pronouncely in PM2.5. (C) 2007 Elsevier Ltd. All rights reserved.