American Association for Aerosol Research - Abstract Submission

AAAR 38th Annual Conference
October 5 - October 9, 2020

Virtual Conference

Abstract View


Long-term Analysis to Elucidate the Origins of Ultrafine Particles in a Major City

HOSNA MOVAHHEDINIA, Nathan Hilker, Cheol H. Jeong, Greg J. Evans, SOCAAR, University of Toronto

     Abstract Number: 357
     Working Group: Urban Aerosols

Abstract
Ultrafine particles are both directly emitted and produced through atmospheric processes. In this research, we explored the origins of ultrafine particles in an urban area by analyzing 15 years of particle size distribution data collected from 2006 to 2020 near a busy roadway in downtown Toronto, Canada, along with meteorological and other pollutant concentration data (NO, NOx, SO2, BC). These data for particle diameters in the range of 6 nm to 560 nm were measured by a Fast Mobility Particle Sizer (FMPS). We manually classified days into five categories: strong nucleation, weak nucleation, midday pollution, traffic pollution, and reference. Strong and weak nucleation days showed long (3hr ≤) or short (< 3hr) nucleation events with a daily-average particle number concentrations of (19±7)×103 and (17±5)×103 #/cm3, respectively. Midday pollution days exhibited higher particle number concentrations around noon with a daily-average of (22±7)×103 #/cm3. The high number concentrations on these days appear to be associated with anthropogenic sources. The traffic pollution days ((20±5)×103 #/cm3) showed morning or afternoon traffic emissions, with no midday rise. Lastly, 46% of the days had lower particle number concentrations ((12±2)×103 #/cm3) throughout the day. Although the number concentrations were lower on these “reference days”, the influence of traffic emissions was still observable in the diurnal pattern. Time series analysis of these categories shows that the occurrence frequency of midday pollution, and strong and weak nucleation days has decreased in recent years with the number of reference days correspondingly increasing. Moreover, meteorological analysis showed that midday pollution days happen more often in winter while strong nucleation days are more frequent in summer.