Research Projects

Project at a Glance

Project Status: complete

Title: Dry deposition onto aerodynamic surfaces and vegetation.

Principal Investigator / Author(s): Wu, Yee Lin

Contractor: Carnegie-Mellon University

Contract Number: A6-186-32


Research Program Area: Atmospheric Processes

Topic Areas: Acid Deposition, Ecosystem Impacts


Abstract:

Aerodynamic surrogate surfaces employing Teflon plates and nylasorb filter paper have been used to measure dry deposition in three sets of field experiments. The first set involves sampling in Claremont during the Southern California Air Quality Study (SCAQS) in June and July 1988. Sampling was conducted at two locations: the Bernard Biological Station and Claremont McKenna College. The second set involves sampling at the same location during an extension of SCAQS in August and September 1988. Finally, the third set includes sampling at Emerald Lake in Sequoia National Park. Three species of vegetation (Waxleaf Privet, Canary island Pine, and Japanese Privet) have also been used to assess dry deposition during the first set of field experiments.

For the first field program, measurable dry deposition fluxes have been obtained for nitrate, sulfate, lead, and calcium. The Teflon plates are shown to yield satisfactory results for sampling periods as short as four hours. The vegetation sampling is shown to yield satisfactory results for periods as short as four days, although it is likely that good results can be obtained for even shorter periods such as 1 - 2 days. The fluxes of all four contaminants on the Teflon plates are highly variable. Values in ng/sec m2 cover the following ranges: nitrate 7 - 213, sulfate 2 - 64, lead 0.035 - 0.46, and calcium 1.2 - 20.7. Results for the Teflon plates and vegetation are roughly comparable. In general, deposition on the Canary Island Pine shows the greatest values, exceeding those on the Teflon plates and nylasorb filter paper by factors of 2 -3. Fluxes onto the Japanese Privet are only slightly lower than those onto Canary Island Pine, while fluxes onto the Waxleaf Privet are nearly the same as those on the Teflon plates and filter paper.

One of the findings of this study is the effect of exposure time on the observed deposition fluxes. Generally, short-term exposures yield greater deposition fluxes for both deposition to the Teflon plates and to vegetation. Resuspension of deposited particles is probably responsible for this phenomenon. Based on the assumed mechanism of resuspension of deposited particles, it is found that the resuspension rates of all four species from any surface are on the order of 10-6 Section 1.

Only limited data are available from the second and third sets of field experiments. The results are generally consistent with the June - July SCAQS data, although nitrate fluxes are considerably smaller at Emerald Lake compared with Claremont. Sulfate fluxes at Emerald Lake are only slightly smaller than in Claremont.


 

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