Variation in airborne particulate matter concentration over the first three metres from ground in a street canyon: implications for human exposure

This note presents vertical concentration profiles of various size fractions of suspended particulate matter, measured over the first three metres from ground in a street canyon, using a novel sampling system. The daily average percentage difference of airborne particulate matter concentration between receptor heights 0.81 and 2.88 m, with the lower height taken as reference, was more than 35% for PM10 and more than 12% for the inhalable fraction, for 5 out of the 7 days of measurement. These preliminary measurements, carried out during June-August 1997, consisting of 37 h of data, corroborate the idea put forward by Colls and Micallef (Atmospheric Environment 31, 4253–4254), that different height groups of the population are exposed to different concentrations. Air-quality standards, based on human exposure estimates, should take this variation into account. These measurements also have implications for the siting of urban air quality monitoring systems.