Dispersion and re-suspension of fine and coarse particulates in an urban street canyon

Dispersion of fine and coarse particulates in the near-field of vehicles has not received as much attention as gaseous pollutants emitted from motor vehicles. Recent studies have pointed to evidence that fine particles in the air could be significant contributors to respiratory and cardiovascular diseases and mortality. This has increased our need to know more about the way particulates disperse in the near-field, especially in street canyons, where pollutants tend to build up to high levels. Movement of vehicles is known to re-suspend particulates deposited on road surfaces resulting in increased pollution levels. This paper presents the results of a study on dispersion of particulate pollution from motor vehicles in urban areas. Levels of airborne fine and coarse particulate matter were measured using two aerosol spectrometers in an urban street canyon in Nottingham, UK. Detailed information on traffic flow and vehicle classification was collected using video recording and sample surveys. The monitoring survey was conducted for one 24-h period in January 1998. There was no direct correlation between fine particulates and traffic volume for 15-min averages. However, there was good correlation between coarse particulates and traffic volume. This prompted a study on the micro-level, at very short time scale, of the effect of vehicle movements on dispersion of particulate pollution in the near-field. Autocorrelation analysis proved that, although there was strong periodicity in traffic flow data, there was none in the levels of coarse and fine particles, suggesting that these levels do not follow the traffic flow pattern. This was confirmed by cross-correlation analysis, which showed no systematic relationship between particulates and traffic volume at different lags.