AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Short-lived Increases in Particle Concentration Disproportionately Influence Exposure to Roadway Air Pollution and Health Outcomes
ROBY GREENWALD, Priya Kewada, Fuyuen Yip, Jeremy Sarnat, Emory University
Abstract Number: 590 Working Group: Urban Aerosols
Abstract The concentration of particulate pollutants on roadways can rapidly change in response to traffic conditions, meteorology, or the proximity of high-emitting vehicles. These changes are not apparent when performing integrated pollutant measurements. Previous investigation has found that the maximum concentrations of several pollutants are stronger predictors of observed health outcomes than integrated concentrations, and it is biologically-plausible that health effects may be driven by short-lived exposure events. To investigate the influence of transitory concentration spikes, the time series of continuously measured in-cabin pollutants from the Atlanta Commuters Exposure (ACE) study were analyzed to determine the frequency and magnitude of events. Measured pollutants include fine particulate matter (PM2.5), particle number concentration (PNC), black carbon (BC) and particle-bound PAHs. If pollutant levels exceeded a threshold value defined as the mean plus one standard deviation (SD) for the entire study and the pollutant concentration increased with a slope exceeding a one SD increase in one minute, an event was triggered. The event was terminated when the concentration reached a local minimum or fell below the threshold value. All pollutants averaged 4-5 events per commute except PM2.5, which averaged less than one. PNC events frequently occurred at different times than BC and PAH events. In many cases, the source(s) of an event could be determined from study data. Although a typical event lasted only a few minutes, the fraction of commute exposure that occurred during an event was double the fraction of time that was during an event. Cumulative event exposure approached 50% of the total and was closely associated with observed health outcomes.