SPATIAL AND TEMPORAL PATTERNS IN SUMMERTIME SULFATE AEROSOL ACIDITY AND NEUTRALIZATION WITHIN A METROPOLITAN AREA

A study of sulfate aerosol acidity in Metropolitan Toronto was conducted during the summer of 1986. Fine-fraction aerosol (<2.5-μm) were collected using Teflon membrane filters and analyzed for major ionic species (H+, NH+4, NO-3, SO2-4). Samples were collected for 6 weeks at three study sites: one in the Center City and the others 13 km (WNW) and 20 km (NE) away. There were very strong correlations among the three sites with respect to measured aerosol species (r2 > 0.9 for 24-h data). However, spatial variations in the magnitude of aerosol acidity were observed during sulfate episodes. For example, the peak concentrations for all sites occurred on 25-26 July 1986. While the 24-h data for sulfate were quite uniform at the three sites (34, 34 and 35 μg m-3), H+ concentrations were 9.4, 8.3 and 6.0 μg m-3 (as H2SO4) for the NE, WNW and Center City sites, respectively. For most of the summertime episodes, the downtown area also had lower aerosol acidity compared to the two sites in suburban areas. © 1989.