Page 251 - Fundamentals of Air Pollution

212 14. Ambient Air Pollutant Analysis and Measurement

of wet deposition are intuitively straightforward. A sample collector opens
to collect rainwater at the beginning of a rainstorm and closes when the
rain stops. The water is then analyzed for pH, anions (negative ions),
and cations (positive ions). The situation for dry deposition is much more
difficult (22). Collection of particles settling from the air is very dependent
on the surface material and configuration. The surfaces of trees, plants,
and grasses are considerably different from that of the round, open-top
canister often used to collect dry deposited particles. After collection, the
material must be suspended or dissolved in pure water for subsequent
analysis.
An overview of acid rain monitoring activities in North America shows
several national and regional programs in operation in the United States,

Fig. 14-9. Wet/dry precipitation collector and flow chart for analysis of samples. (Dl H 2O:
distilled water). Source: "NADP Quality Assurance Report," Central Analytical Laboratory,
Illinois Institute of Natural Resources, Champaign, 111., March 1980.