Air Pollution and Physical Activity (APPA): Air Pollution Exposure in Travel Modes

Abstract

IntroductionTravel microenvironments are often the most polluted places people encounter in their daily lives. Encouraging walking and cycling may increase physical activity in the population, but also lead to higher intakes of pollutants (due to high inhalations rates in highly contaminated environments). Quantification of exposure contrasts between travel modes is needed to estimate potential risks and benefits of walking/cycling.MethodA systematic review of global literature comparing exposures while walking and cycling to other modes (car, bus, overground/underground rail) was conducted. Data from the disparate set of studies was harmonized to estimate ratios of concentrations in active travel vs motorized travel modes for fine particulate matter (PM2.5), ultrafine particles (UFP), black carbon (BC) and carbon monoxide (CO). Comparisons were made for ratios obtained in different continents.ResultsOf 280 articles examined, 27 responding to inclusion criteria were retained for analyses. Most were derived from European studies although all continents except Antarctica were represented. Globally, walking was amongst the least exposed travel modes for BC and CO, with more inconsistent results for PM2.5 and UFP. Cycling was amongst the most exposed for UFP, and the least exposed for BC (other than walking). Results varied by continent.ConclusionA large variety of study designs and settings makes a unified picture of air pollution contrasts between travel modes difficult. Nevertheless the ratios and associated confidence intervals obtained provide useful metrics for health impact modelling, enabling a comprehensive analysis of risk and benefit tradeoffs of walking and cycling policies in urban environments.