Determinants of fine particle (PM2.5) personal exposure levels in transport microenvironments, London, UK

A series of field studies were carried out in London, UK, during 1999-2000 in which over 400 fine particle (PM2.5) personal exposure level measurement s were taken for journeys in bicycle, bus, car and underground rail transpo rt microenvironments, This was the first comprehensive PM2.5 personal expos ure study of transport users. Both a fixed route multi-transport mode study and a study of cyclists' commuter journeys were undertaken. Subsequent to these field studies regression modelling of possible influencing factors of these exposure levels was carried out. Meteorological variables, traffic d ensity, mode and route were considered; the relationships of personal expos ure levels with fixed site monitor (FSM) concentrations, and of the FSM con centrations with the potential predictor variables, were also investigated. This analysis of the determinants of transport user exposure to PM2.5 in L ondon, UK, showed that wind speed had a significant influence on personal e xposure levels, though explained only up to 20% of the variability of road transport user exposure levels. The occurrence of higher wind speeds was st rongly associated with a decrease in personal exposure levels; a 1.5-2.0 fo ld difference in exposure level concentrations was estimated between the 10 th and 90th percentiles of wind speed. Route was a significant factor, whil st mode was not a significant factor in the street microenvironment (betwee n bicycle, bus and car modes); models incorporating route and mode, as well as wind speed, explained approximately 35% of the variability in PM2.5 exp osure levels. Personal exposure levels were reasonably correlated with urba n background FSM concentrations, for fixed-route road mode (bicycle, bus an d car) exposure level concentrations, r = 0.27 (p <0.01) and for commuter c yclists' exposure level concentrations r = 0.58 (p <0.01). (C) 2001 Elsevie r Science Ltd. All rights reserved.