Ultrafine particles near a major roadway in Raleigh, North Carolina: Downwind attenuation and correlation with traffic-related pollutants

Ultrafine particles (UFPs, diameter < 100 nm) and co-emitted pollutants from traffic are a potential health threat to nearby populations. During summertime in Raleigh, North Carolina UFPs were simultaneously measured upwind and downwind of a major roadway using a spatial matrix of five portable industrial hygiene samplers (measuring total counts of 20-1000 run particles). While the upper sampling range of the Portable samplers extends past the defined "ultrafine" upper limit (100 nm), the 201000 nm number counts had high Correlation (Pearson R = 0.7-0.9) with UFPs; (10-70 nm) measured by a co-located research-grade analyzer and thus appear to be driven by the Ultrafine range. Highest UFP concentrations were observed during weekday morning work commutes, with levels at 20 m downwind from the road nearly fivefold higher than at an upwind station. A strong downwind spatial gradient was observed, linearly approximated over the first 100 in as an 8% drop in UFP Counts per 10 in distance. This result agreed well with UFP spatial gradients estimated from past studies (ranging 5-12% drop per 10 in). Linear regression of other vehicle-related air Pollutants measured in near real-time (10-min averages) against UFPs yielded moderate to high correlation with benzene (R-2 = 0.76), toluene (R-2 = 0.49), carbon monoxide (R-2 = 0.74), nitric oxide (R-2 = 0.80), and black carbon (R-2 = 0.65). Overall, these results support the notion that near-road levels of UFPs are heavily influenced by traffic emissions and correlate with other vehicle-produced Pollutants, including certain air toxics. Published by Elsevier Ltd.