Trip motive in time and space: the impact on black carbon exposure

Abstract

Background: Exposure in transport contributes to almost a quarter of accumulated exposure over a day, however in Flanders individuals travel for only 6% of the time. Evidence is emerging that high concentration peaks, for example in transport, are responsible for important health effects. Objectives: We evaluate trips with different motives, and try to discover spatial and temporal characteristics typical for trips with a specific motive. The effect on in-traffic exposure to Black Carbon (BC) is assessed. Methods: In 2010, 62 people volunteered to participate in a Flemish study examining personal exposure to the air pollutant BC using portable µ-aethalometers. The participants were also equipped with an electronical diary to register activities and trips. A Global Positioning System was built in the handheld computer and tracked the trips of volunteers. Results: Over 1500 trips were registered, and assigned by the participants to 6 modes of transport. Trip motive was defined as one of 10 activities performed at the destination side of a trip (only if this was a home-based activity, the diary entry at the origin was defined as trip motive). 61% of all trips with motive work were on weekday peak hours. Half of social and leisure trips are in the weekend and another third is on off-peak hours. Transport modes are distributed quite evenly over trips with different motives. More than 50% of all non-rail commute trips are on highways or on other major roads, daily shopping trips are mainly driven on local roads. As a result, average exposure during commute trips is highest (5.7 µg/m³). Exposure during daily shopping trips is much lower (4.0 µg/m³). In addition, commute trips have almost twice the duration of daily shopping trips. Conclusions: Average concentrations encountered during trips with different motives, are mainly driven by the timing of those trips and road choice. Exposure to BC is highest during car commute trips.