AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Exposure to Outdoor Ultrafine Particles: Role of Traffic and Atmospheric New Particle Formation
SHAHZAD GANI, Kyle Messier, Joshua Apte, University of Texas at Austin
Abstract Number: 330 Working Group: Urban Aerosols
Abstract Ultrafine particles (UFP) (d$_p<0.1 micrometer) may pose important health risks. However, routine monitoring of UFP is still uncommon in most urban areas. We exploit time-resolved particle number concentration (PN) data from an extensive monitoring network in the San Francisco Bay Area to investigate the contributions of primary emissions, meteorology and new particle formation to space-time patterns of urban UFP. Our analysis incorporates ~4 years of hourly data from a network of 6 condensation particle counters (CPCs) operated by the Bay Area Air Quality Management District. Overall annual-average PN span a range of ~3 × 10$^3 cm$^(-3) at a semi-rural site to ~30 × 10$^3 cm$^(-3) at a near-road site near a major freeway with heavy truck traffic.
We observe a strong influence of traffic on PN levels: near-freeway sites show consistently higher PN than more distant sites. By separating weekdays and weekends, we observe impacts of primary sources such as traffic. For near-freeway sites, we employ traffic data to investigate the contribution of vehicles to elevated PN concentrations. Seasonal variations in ventilation modulate the effect of primary emissions. Stagnant conditions lead to elevated levels of PN and other gaseous combustion tracers (CO, NO) on winter nights relative to winter days. In contrast, strong midday peaks in PN lasting 5-7 h occur on most days in summer months, reaching concentrations similar in magnitude to those on winter nights. Because these mid-day peaks are evident at all PN monitoring sites, yet absent in the time series of any other measured pollutant, we hypothesize that they are the result of atmospheric new particle formation.
Our preliminary findings suggest that new particle formation and primary emissions may each contribute in similar magnitude to urban background PN levels during summer days in the San Francisco Bay Area.