TEMPORAL AND SPATIAL RELATIONSHIPS IN FINE-PARTICLE STRONG ACIDITY, SULFATE, PM10 AND PM2.5 ACROSS MULTIPLE CANADIAN LOCATIONS

The Canadian Acid Aerosol Measurement Program (CAAMP) was established in 1992 to gain a better understanding of the atmospheric behaviour of fine particle strong acidity (''acid aerosols'') and to facilitate an assessment of the potential health risks associated with acid aerosol s and particles in general. During 1992, 1993 and 1994, annular denude r and filter measurements were taken at four sites in Ontario, two in Quebec, three in the Atlantic Provinces and one in the greater Vancouv er area. Mean fine particle sulphate concentrations (SO42-) were highe st in southern Ontario (annual average ranged from 40-70 nmol m(-3)), lowest at a site in the Vancouver area (average = 16 nmol m(-3)) and s econd lowest in rural Nova Scotia. However, mean fine particle strong acid concentrations (H+) were geographically different. The highest me an concentrations were at the east coast sites (annual average of up t o 30 nmol m(-3)). Acidities were lower in areas where the fine particl e acidity experienced greater neutralization from reaction with ammoni a. This included the major urban centres (i.e. Toronto and Montreal) a nd areas with greater amounts of agricultural activity, as in rural so uthern Ontario. On average, ambient concentrations of fine and coarse particle mass were larger in the urban areas and also in areas where S O42- levels were higher. All the particle components were episodic. Ho wever, compared to SO42- and fine particles (PM2.5 or PM2.1, depending upon inlet design), episodes of H+ tended to be less frequent and of shorter duration, particularly in Ontario. Saint John, New Brunswick, had the highest mean annual H+ concentration, which was 30 nmol m(-3). H+ episodes (24 h concentration > 100 nmol m(-3)) were also the most frequent at this location. The high levels in Saint John were partiall y due to local sulphur dioxide sources and heterogeneous chemistry occ urring in fog, which, on average, led to a 50% enhancement in sulphate , relative to upwind conditions. There was a substantial amount of int ersite correlation in the day to day variations in H+, SO42-, PM2.5 an d PM10 (fine + coarse particles) concentrations, which is due to the i nfluence of synoptic-scale meteorology and the relatively long atmosph eric lifetime of fine particles. Sulphate was the most regionally homo genous species. Pearson correlation coefficients comparing SO42- betwe en sites ranged from 0.6 to 0.9, depending on site separation and lag time. In many cases, particle episodes were observed to move across th e entire eastern portion of Canada with about a two-day lag between th e SO42- levels in southern Ontario and in southern Nova Scotia. (C) 19 97 Elsevier Science Ltd.