Use of the integrated organic gas and particle sampler to improve the characterization of carbonaceous aerosol in the near-road environment

Particle phase organic carbon (OC), elemental carbon (EC) and particle phase semi-volatile organic carbon were measured simultaneously at two distances downwind of a highway using an integrated organic gas and particle sampler. This method reduces sampling artifacts associated with OC measurement. On average, artifact-corrected OC (referred to as OCT) was 2.4 μg/m3 and the positive and negative artifacts were significant at 0.8 and 1.0 μg/m3 respectively. Close to the highway negative artifacts are potentially dominant over positive artifacts indicating that traditional integrated filter-based sampling for OC and fine particles (PM2.5) may be biased low. Decreases in OCT between the near and far site ranged from 25 to 44% while the decreases observed for EC, which reflects the impact of dispersion, were larger at 42-84%. The nature of the OCT changed between sites becoming less volatile and having a greater content of pyrolized organic carbon. Collectively, these results suggest that secondary organic aerosol (SOA) formed downwind of the highway from vehicle-related emissions and was detectable within the 15 min transit time between the highway and the far site. These results highlight the need for improvements in understanding the processes influencing organic aerosols in locations directly impacted by motor vehicle emissions in order to realistically predict PM2.5 using air quality models.