A field intercomparison of methods for the measurement of particle and gas dry deposition

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Abstract
Concurrent measurements of the dry deposition of sulfate, particulate sulfur, nitrate, sulfur dioxide, ozone, and nitric acid were made during September 1981 and June 1982, using several independent methods. The measurements were conducted at a common site, which was a grasscovered 32‐ha field in a topographically flat, rural area 14 km southwest of Champaign, Illinois. Research groups from 14 U.S. and Canadian institutions participated in the study, which was coordinated by the Illinois State Water Survey. Micrometeorological methods such as eddy correlation, variance, concentration gradient/modified Bowen ratio calculation, and eddy accumulation were used. Deposition collection methods such as surrogate surface sampling and vegetation washing were also employed. Sampling schedules and heights of measurements were arranged to maximize the comparability of results from the various flux determination techniques. Sulfate and particulate sulfur mean deposition velocities, vd, on the order of 0.3 cm/s were found by several methods. Nighttime values were small, generally near zero, while daytime vd of up to 1.0 cm/s were observed. A possibly significant contribution to the total sulfur flux by large (diameter >2.0 μm) particle associated sulfate was noted in some periods. Daytime sulfur dioxide and nitric acid vd of greater than 3.0 cm/s were measured, suggesting near‐zero vegetation canopy resistance to mass transfer for these gases.

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