Air pollution, Short term, Ultrafine particles, Soot
Recent interest has focused on the health effects of ultrafine particles because of the documented toxicity and the larger concentration contrast near motorways of UFP than for PM10 or PM2.5. There are only few studies that have measured UFP at inner-city streets simultaneously with other PM components. The aim of this study was to compare the contrast of UFP, PM(10) and soot measured simultaneously at 3 inner-city locations, namely a moderately busy street (15,000 vehicles/day), a city and a suburban background location. Simultaneously, measurements of particle number concentrations (PNC), PM(10) and soot have been conducted on three locations in and around Utrecht, a medium-sized city in the Netherlands for 20 weekdays in autumn 2008. Measurements were done for 6-h during afternoon and early evening. The mean PNC at the street location was more than 3 times higher than at the two background locations. The contrast was similar for soot concentrations. In PM(10) concentrations less contrast was found, namely 1.8 times. Mean PNC concentrations were poorly correlated with PM(10) and soot. At the street location, high temporal variation of PNC concentrations occurred within each sampling day, probably related to variations in traffic volumes, high-emission individual vehicles and wind direction. Temporal variation was smaller at the two background locations. Occasional unexplained short-term peaks occurred at the suburban background location. A relatively high correlation between PNC minute values at the two background locations was found, pointing to similar area-wide sources. Typically low correlations were found with the street locations, consistent with the dominant impact of local traffic. A large contrast between two background locations and a moderately busy urban street location was found for PNC and soot, comparable to previous studies of much busier motorways. Temporal variation of PNC was higher at the street location and uncorrelated with background variations.