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Principal Investigator: Yee Lin Wu
Carnegie-Mellon University, Pennsylvania
17 February 1989
ARB Contract No. A6-186-32 (Full Report)
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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