Determining the Fate of PM 2.5 Particles Following Capture by Leaves (05-DG-11233225-228)

Study of PM 2.5 deposition, re-suspension and wash off from leaves under controlled conditions, and dispersion of PM 2.5 near roads and the effect of vegetation on dispersion patterns.

This project studied particulate matter (PM) 2.5 deposition, re-suspension and wash off from leaves under controlled conditions, and dispersion of PM 2.5 near roads and the effect of vegetation on dispersion patterns. Our prior work indicates that net deposition occurs at low rates, with little effect on the concentration remaining in the air. This study found that for leaf types ranging from small needles (hemlock) to broadleaved species (Norway maple) and wind speeds up to 30 mph, re-suspension of PM 2.5 was nil. In contrast, simulated rainfall amounting to ca 0.2 " rinsed> 50% of the PM 2.5 from leaf surfaces and 0.4" reduced leaf loads to background detection limits. Dose-response studies showed that while different leaf types accumulated different amounts of PM 2.5, there was no indication of saturation even with exposure to extreme doses. Outdoor monitoring campaigns show that local PM2.5 sources such as vehicular traffic increase human exposure by orders of magnitude, yet these transient spikes go undetected by official monitors. These local plumes dissipate rapidly with distance regardless of tree cover, but a dense hedge appears to contribute to the magnitude of reduction.

Attachments

Click here to download this file.