Improved measurement of seasonal and diurnal differences in the carbonaceous components of urban particulate matter using a denuder-based air sampler

Abstract

A denuder-based integrated organic gas and particle sampler (IOGAPS), designed to minimize artifacts often encountered during conventional filter pack (FP) sampling, was used in this study to examine seasonal and diurnal variations of particle-bound organic carbon (OC) and elemental carbon (EC) in Toronto, Canada. Daytime and nighttime PM2.5 samples were collected using both the IOGAPS and FP in Toronto from 16-21 July 2001 and 17-24 March 2003. The average OC determined by the IOGAPS (IOGAPS-OC) was 6.7 μg C/m 3 in July 2001 and 5.3 μg C/m3 in March 2003. The average EC determined by the IOGAPS (IOGAPS-EC) was 0.9 μg C/m3 and 0.4 μg C/m3, respectively, during these periods. The IOGAPS-OC concentrations were often higher during the night. This could be explained by the partitioning of the gas phase semivolatile organic carbon (SVOC) onto the existing aerosols due to decreased ambient temperatures. The average of the SVOC measured by the IOGAPS was 0.5 μg C/m3 and 4.5 μg C/m 3 during the day and night in July 2001, respectively. In March 2003 the daytime average SVOC was 1.9 μg C/m3 and the nighttime average SVOC was 2.5 μg C/m3. The formation of secondary organic aerosols (SOA) contributed significantly to the summertime OC in July 2001, which was confirmed by a poor correlation between the IOGAPS-OC and IOGAPS-EC (R 2 = 0.01). In contrast, a relatively strong correlation between IOGAPS-OC and IOGAPS-EC (R2 = 0.87) during the winter in March 2003 suggests that the main sources of the carbonaceous aerosols were primary.