Temporal and spatial relationships in fine particle strong acidity, sulphate, PM 1O, and PM 2.5 across multiple canadian locations

Abstract

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 aerosols and particles in general. During 1992. 1993 and 1994, annular denuder and filter measurements were taken at four sites in Ontario, two in Quebec, three in the Atlantic Provinces and one in the greater Vancouver area. Mean fine particle sulphate concentrations (SO 4 2−) were highest 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 second lowest in rural Nova Scotia. However, mean fine particle strong acid concentrations (H +) were geographically different. The highest mean concentrations were at the east coast sites (annual average of up to 30 nmol m −3). Acidities were lower in areas where the fine particle acidity experienced greater neutralization from reaction with ammonia. This included the major urban centres (i.e. Toronto and Montréal) and areas with greater amounts of agricultural activity, as in rural southern Ontario. On average, ambient concentrations of fine and coarse particle mass were larger in the urban areas and also in areas where SO 4 2− levels were higher. All the particle components were episodic. However, compared to SO 4 2− and fine particles (PM 2.5 or PM 2.1, 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 partially due to local sulphur dioxide sources and heterogeneous chemistry occurring in fog, which, on average, led to a 50% enhancement in sulphate, relative to upwind conditions. There was a substantial amount of intersite correlation in the day to day variations in H +, SO 4 2− , PM 2.5 and PM 10 (fine + coarse particles) concentrations, which is due to the influence of synoptic-scale meteorology and the relatively long atmospheric lifetime of fine particles. Sulphate was the most regionally homogenous species. Pearson correlation coefficients comparing SO 4 2− between 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 the entire eastern portion of Canada with about a two-day lag between the SO 4 2− levels in southern Ontario and in southern Nova Scotia.