during walking and in-car journeys on two suburban routes in Northampton, UK, during the winter of 1999/2000.
Comparisons were made between concentrations found in each transport mode by particle fraction, between different
particle fractions by transport mode, and between transport microenvironments and a fixed-site monitor located within
the study area. High levels of correlation were seen between walking and in-car concentrations for each of the particle
fractions (PM10: r2 ¼ 0:82; PM2.5: r2 ¼ 0:98; PM1: r2 ¼ 0:99).
On an average, PM10 concentrations were 16% higher inside the car than for the walker, but there were no difference in average PM2.5 and PM1 concentrations between the two modes. High PM2.5:PM10 ratios (0.6–0.73) were found to be associated with elevated sulphate levels. The PM2.5:PM10 and PM1:PM2.5 ratios were shown to be similar between walking and in-car concentrations. Concentrations of PM10 were found to be more closely related between transport mode than either mode was with concentrations recorded at the fixed-site (roadside) monitor. The fixed-site monitor was shown to be a poor marker for PM10 concentrations recorded during walking and in-car on a route over 1 km away.