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Measuring Pedestrian Exposure to PM-2.5: Case of the Seattle, Washington, International District

Traffic-related air pollution is dangerous to human health. Although transportation and land use planning policies often focus on making walking more attractive, there is a lack of research on pedestrian exposure to air pollution levels. This research focused on pedestrian exposure to particulate matter with a diameter of 2.5 µm or less (PM-2.5) in the International District (ID) adjacent to downtown Seattle, Washington. Several types of equipment were used: (a) a portable nephelometer (Radiance Research M903) mounted on a backpack (arranged by the Puget Sound Clean Air Agency); (b) an AirCasting mobile application (by Habitmap) in a cell phone to record the researcher’s location and exposure levels while walking; and (c) a GoPro Hero camera to record visual images of the surrounding built environment, traffic volume, and other activities. The field data were collected three times a day (morning, midday, and evening) for one week in winter (December 31, 2014–January 9, 2015) and one week in spring (March 21–30, 2015) on selected routes in the ID. The study found seasonal and time-of-day variability of exposure levels: there were higher PM-2.5 concentration levels during the winter (57.77 µg/m3) than in the spring (6.99 µg/m3), and higher levels in the morning (25 µg/m3) than in the evening (17 µg/m3). Also, the average PM-2.5 levels of ID data were slightly higher (20.7 µg/m3) than those at the nearest U.S. Environmental Protection Agency monitoring station (19.0 µg/m3). The researchers concluded that the key contributors of pedestrian exposure to air pollution are traffic, construction activities, and smokers on sidewalks.