AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Spatiotemporal Profiles of Ultrafine Particles Differ from Other Traffic-Related Air Pollutants: Lessons from Long-Term Measurements at Fixed Sites and Mobile Monitoring
SHAHZAD GANI, Sarah Chambliss, Kyle Messier, Melissa M. Lunden, Joshua Apte, University of Texas at Austin
Abstract Number: 891 Working Group: Urban Aerosols
Abstract The health risks of ultrafine particle (UFP, Dp<100 nm) exposure are an important subject of current investigation in air pollution epidemiology. With routine monitoring of UFP still uncommon, health studies often use other pollutants as proxy for UFP. Here, we use two rich datasets — one with high spatial coverage, and the other with high temporal coverage — to investigate how the spatial-temporal patterns of UFP relate to other traffic-related air pollutants, especially NOx. We incorporate 3–6 years of hourly particle number (PN) concentration data from multiple fixed sites across the San Francisco Bay Area that include near-highway, urban, suburban and rural sites. In addition, we incorporate observations from a 32-month mobile monitoring campaign comprising >3,000 h of coverage of a range of road types and land uses.
Overall annual-average PN at the fixed sites span a range of 3 × 103 cm−3 at rural site to 30 × 103 cm−3 at near-highway site. Across all sites, PN measurements on nearly all summer days show consistent, prominent mid-day peaks, lasting 5–7 h. This diurnal concentration pattern—characteristic of new particle formation — is not observed for other co-emitted pollutants (NOx, BC, CO). While we found moderate correlation in diurnal patterns of NOx and UFP at sites with high traffic, the correlation dropped significantly for low traffic areas — especially during high insolation (e.g., summer daytime) periods. Mobile monitoring data yielded similar results: NOx was observed to have weaker correlations with UFP for non-highway roads during high insolation periods. UFP in urban atmosphere is known to result primarily from vehicular traffic and photonucleation events. As a result, the spatiotemporal profiles of UFP can differ strongly from other traffic-related air pollutants when new particle formation from photonucleation contribute to a significant fraction of UFP.