MONITORING IMPACTS OF MASS-TRANSIT VEHICLES ON PARTICULATE MATTER CONCENTRATIONS IN URBAN ENVIRONMENTS USING MAGNETIC PROPERTIES OF TREE LEAVES: PILOT STUDY OF BUS AND BIKE ROUTES IN BELLINGHAM, WA

Particulate matter pollution in the urban environment is increasingly recognized as a significant health hazard; in particular a category of ultra-fine particles (less than 10 µm diameter, referred to as PM10) may warrant additional study and monitoring as these particles can bypass all airway defenses and be inhaled deeply into lung tissue. In urban environments PM10 particles have been found to originate from a variety of sources ranging from natural dust, to fly-ash produced by fossil fuel combustion, and motor vehicle related particles (mainly brake, tire, and road material). Many studies have found that biological sample collectors such as tree leaves act as effective means of monitoring particulate matter and that magnetic measurements can serve as effective and efficient means of determining particulate matter composition, size, and concentrations. PM10 concentrations and sources are poorly studied in the Pacific NW. In many communities heavily travelled bus routes serve as high-traffic pedestrian and bike commuter routes in cities such as Bellingham, WA, but few studies have been conducted to assess the effects of particulate matter pollution on pedestrian and bike commuters.We collected leaves primarily from Bigleaf Maple (Acer macrophyllum). Trees were selected on several streets in Bellingham that serve as shared high-capacity bus and bike routes to the WWU campus, streets paralleling these high traffic streets that lack bus traffic entirely, and control sites located away from Bellingham. Leaves were collected in late June 2009, with repeat collections scheduled for August and late September. Each leaf was weighed, and then placed in a sample holder for magnetic measurements, which were conducted within three days of collection. Results of magnetic hysteresis, ARM, and IRM acquisition reveal that leaves record measurable concentrations of particulate matter. Leaves from trees adjacent to bus routes have Ms values that are 2 to 8 times higher than those from parallel streets lacking bus traffic, and 4 to 10 times that of leaves in rural settings. Collectively these initial results indicate that bike and pedestrian commuters who share high traffic bus routes experience significantly elevated exposure to metallic particulate matter.