Spatial variations of non-exhaust emissions across seasons using fixed-site and mobile measurements

Urban exposure to particulate matter (PM) from road dust and brake and tire wear (BTW) is an emerging health concern. Mobile and fixed-site PM sampling was conducted seasonally in Toronto. Mobile sampling employed paired window and wheel-well inlets to estimate resuspended PM, alongside ultrafine particles and black carbon as indicators of exhaust emissions. Analysis of 900+ weekly filters from 40 sites showed the strongest roadway contrasts for barium. Source apportionment resolved distinct contributions from road dust and BTW. Road dust dominated the trace element mass in PM, peaking in construction areas, while BTW contributed 10–15 % and peaked near expressways. Mobile measurements revealed steep near-road ultrafine particle gradients and increased resuspended PM on local roads, particularly in winter. However, non-exhaust emission rates remained greatest on expressways. This study presents the first integration of fixed-site and mobile measurements with spatial source apportionment and land use regression with kriging to characterize non-exhaust emissions.