Carbonaceous and ionic components in wintertime atmospheric aerosols from two New Zealand cities: Implications for solid fuel combustion

Wintertime PM10 samples collected in two New Zealand cities (Christchurch and Auckland) have been analysed for total carbon (TC), elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC), and water-insoluble organic carbon (WIOC) as well as major inorganic ions. Christchurch, which is heavily influenced by residential wood and coal burning in winter, showed significantly higher ambient concentrations of carbonaceous materials than Auckland whose major sources of aerosols are sea-salt and vehicular emissions. In Christchurch, the mean concentrations of TC, EC, WSOC, and WIOC were 21, 6.0, 7.0 and 7.6 μg m−3, respectively. In contrast, those of Auckland were 5.0, 2.0, 1.3 and 1.7 μg m−3, respectively. On average, total carbonaceous materials (EC, water-soluble organic matter and water-insoluble organic matter) accounted for about 70% of PM10 mass in Christchurch but less than 30% in Auckland. Moreover, WSOC/EC and nss-K+/EC mass ratios in Christchurch were found to be substantially higher than those of Auckland. In contrast, nss-SO42−, NO3− and nss-Ca2+ concentrations in Auckland were dramatically enhanced relative to carbonaceous materials. This study suggests that fresh emissions from solid fuel burning are significantly more enriched with WIOC than WSOC, although a significant fraction of WSOC may be a secondary atmospheric product. It is estimated that only one-fifth to one-quarter of the measured OC was attributable to secondary organic aerosols in the two cities in winter.