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 PM _2.5 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 μ g C/m^bm3 in July 2001 and 5.3 μ g C/m^bm3 in March 2003. The average EC determined by the IOGAPS (IOGAPS-EC) was 0.9 μ g C/m^bm3 and 0.4 μ g C/m^bm3, 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 μ g C/m^bm3 and 4.5 μ g C/m^bm3 during the day and night in July 2001, respectively. In March 2003 the daytime average SVOC was 1.9 μ g C/m^bm3 and the nighttime average SVOC was 2.5 μ g C/m^bm3. 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^bm2 = 0.01). In contrast, a relatively strong correlation between IOGAPS-OC and IOGAPS-EC (R^bm2 = 0.87) during the winter in March 2003 suggests that the main sources of the carbonaceous aerosols were primary.

Acknowledgments

The financial support for this study was from the Toxic Substances Research Initiative, Government of Canada. We thank Dr. Douglas A. Lane and Dr. Cristian Mihele of Meteorological Service of Canada (MSC) of Environment Canada for the training of denuder coating and SIF preparation, and Dr. Lara A. Gundel of Lawrence Berkeley National Laboratory for technical discussion. We also thank Melynda Bitzos of Ontario Ministry of Environment for providing us with ozone data collected in downtown Toronto.