American Association for Aerosol Research - Abstract Submission

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

Virtual Conference

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Trends in Inter- and Intra-Urban Ultrafine Particle Concentrations in North America: Exposure Implications

ALBERT PRESTO, Provat Saha, Allen Robinson, Carnegie Mellon University

     Abstract Number: 50
     Working Group: Aerosol Exposure

Abstract
The climatology of ultrafine particles (UFP; particles smaller than 100 nm) has been extensively studied for their ability to grow into cloud condensation nuclei and thereby impact Earth’s climate. Human exposures to UFPs are also of concern because these particles, which are not directly regulated in the U.S., may have distinct health effects from exposure to PM2.5 mass. However, less is known about temporal and spatial trends in UFPs and how these trends impact exposure. This talk will address several exposure-relevant questions about UFP: (1) What are typical concentrations? (2) What are the long-term temporal trends? (3) What are inter- and intra-urban spatial patterns? (4) What are the major UFP sources, and how do they drive observed spatial patterns? (5) What are contributions of primary and secondary UFPs to human exposure? (6) Can existing monitoring data be used to estimate national-scale exposures for use in epidemiology?

We will answer these questions by synthesizing a combination of new/unpublished data and results from the literature. These data include long-term (>1 year) measurements in eight cities along with mobile sampling data collected in three cities (Baltimore, Oakland, and Pittsburgh). Since UFPs share many common sources with primary PM2.5 and secondary PM2.5 precursors, concentrations of both UFP and PM2.5 have fallen by ~35% over the past 15 years. UFP exhibit large spatial variability; concentrations vary by a factor of 2-3 within cities, and mean concentrations vary by about a factor of two across cities. A major driver of both the long-term temporal trends and the intra-city spatial patterns are emissions from vehicles. The importance of vehicular emissions highlights that in urban areas, UFP are dominated by primary emissions rather than secondary particles.