Exploring variability in pedestrian exposure to fine particulates (PM2.5) along a busy road

In August 2006, pedestrian exposure to PM2.5 was monitored along a busy roadway in Sydney, Australia. The objective of the campaign was to assess the factors affecting exposure at both an inter- and intra-trip level. PM2.5 measurements were made at second-by-second intervals using a portable aerosol monitor, while simultaneously recording location with a personal GPS device. A digital voice recorder was used to record any events or circumstances, perceived to notably increase potential PM2.5 levels. The average PM2.5 concentration for the 39 trips conducted was 12.8 μg m−3, which while 40% higher than concurrent ambient measurements was well within proposed daily standards for Australia. Multivariate time-series methods were then applied to study the effects of various interventions on PM2.5 at an intra-trip level while controlling for autocorrelation. Wind speed, traffic volumes and clearway operations (independent of traffic volumes) were found to be significant predictors in addition to the previous PM2.5 concentrations. Sensitivity analysis showed doubling traffic volumes increased PM2.5 concentrations by 26%, while each 5 km h−1 increase in wind speed increased PM2.5 concentrations by 10%. Several PM2.5 hotspots were identified where concentrations exceeded 100 μg m−3. These were attributed to specific traffic (intersections, trucks, buses) and non-traffic sources (pedestrians smoking), typically only lasting a few seconds.