AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Characterization of Black Carbon and Polycyclic Aromatic Hydrocarbon Plume Events in Near-Source Microenvironments Using a Mobile Sampling Platform
TIMOTHY DALLMANN, Peishi Gu, Yi Tan, Allen Robinson, Albert A. Presto, Carnegie Mellon University
Abstract Number: 131 Working Group: Urban Aerosols
Abstract In some urban microenvironments dominated by traffic or point source emissions, short time duration plume events spanning intervals ranging from seconds to tens of minutes can result in elevated air pollutant concentrations and disproportionately impact exposures for nearby populations. Central monitoring networks, generally designed to obtain hourly and daily average pollutant concentrations representative of a regulatory airshed, may not be well suited to assess these short term, localized events.
To explore the importance of source plume events, we conducted over 200 hours of sampling at 36 sites in Allegheny County, Pennsylvania in summer 2013 and winter 2013-2014 using a mobile measurement platform. Site selection was stratified according to three control variables: elevation, proximity to traffic, and proximity to point sources, allowing for investigation of a broad range of source influences. In-situ measurements of black carbon (BC) and particle-bound polycyclic aromatic hydrocarbons (PAH) were conducted using continuous instrumentation. Supporting measurements of gas phase species including nitrogen oxides, carbon dioxide (CO2), and volatile organic compounds were also made. Most instruments were operated with a time resolution of less than 10 seconds, allowing for the characterization of source related plume events.
Preliminary results indicate small numbers of plume events can heavily influence hourly average BC and PAH concentrations, with strong local source contributions particularly evident at sampling sites in close proximity to diesel sources (e.g. near roadways and rail lines). For example, intermittent plume events contributed greater than 80% of the total PAH measured at several high traffic sampling locations. In these cases, where PAH concentrations can vary over several orders of magnitude, hourly average concentrations do not provide an adequate representation of short term exposure conditions. Pollutant ratios (e.g. PAH/BC) and ratios of pollutants to CO2 for individual plume events provide further information on emission profiles for the various source types encountered.