Page 252 - Fundamentals of Air Pollution

References 213

Canada, and Mexico (23). The National Atmospheric Deposition Program
has established the nationwide sampling network of —100 stations in the
United States. The sampler is shown in Fig. 14-9 with a wet collection
container. The wet collection bucket is covered with a lid when it is not
raining. A sensor for rain moves the lid to open the wet collector bucket
and cover the dry bucket at the beginning of a rainstorm. This process is
reversed when the rain stops.
The primary constituents to be measured are the pH of precipitation,
sulfates, nitrates, ammonia, chloride ions, metal ions, phosphates, and
specific conductivity. The pH measurements help to establish reliable long-
term trends in patterns of acidic precipitation. The sulfate and nitrate infor-
mation is related to anthropogenic sources where possible. The measure-
ments of chloride ions, metal ions, and phosphates are related to sea spray
and wind-blown dust sources. Specific conductivity is related to the level
of dissolved salts in precipitation.
Figure 14-9 also shows a flowchart for analysis of wet and dry precipita-
tion. The process involves weight determinations, followed by pH and
conductivity measurements, and finally chemical analysis for anions and
cations. The pH measurements are made with a well-calibrated pH meter,
with extreme care taken to avoid contaminating the sample. The metal ions
2+
+
+
2+
Ca , Mg , Na , and K are determined by flame photometry, which
involves absorption of radiation by metal ions in a hot flame. Ammonia
3
2
and the anions Cl~, SO 4 ~", NO 3", and PO 4 " are measured by automated
colorimetric techniques.
REFERENCES
1. Dailey, W. V., and Fertig, G. H., Anal. Instrum. 77, 79-82 (1978).
2. U.S. Environmental Protection Agency, 40 CFR, Part 50, App. C, July 1992.
3. Stevens, R. K., and Hodgeson, J. A., Anal. Chem. 45, 443A-447A (1973).
4. U.S. Environmental Protection Agency, "Transfer Standards for Calibration of Air Moni-
toring Analyzers for Ozone," EPA-600/4-79-056. Office of Air Quality Planning and Stan-
dards, Research Triangle Park, NC, 1979.
5. U.S. Environmental Protection Agency, Fed. Regist. 41, 52686-52695 (1976).
6. U.S. Environmental Protection Agency, 40 CFR, Part 50, App. A, July 1992.
7. Hollowell, C. D., Gee, G. Y., and Mclaughlin, R. D., Anal. Chem. 45, 63A-72A (1973).
8. Okake, H., Splitstone, P. L., and Ball, J. J., /. Air Pollut. Control Assoc. 23, 514-516 (1973)
9. National Oceanic and Atmospheric Administration, "United States Standard Atmo-
sphere." U.S. Government Printing Office, Washington, DC, 1976.
10. Lodge, J. P. (ed.), "Methods of Air Sampling and Analysis," 3rd ed. American Public
Health Association, Washington, DC, 1989.
11. Liu, B. Y. H., Pui, D. Y. H., and Kapadia, A., Electrical aerosol analyzer, in "Aerosol
Measurement" (Lundgren, D. A., Harris, F. S., Jr., Marlow, W. H., Lippmann, M., Clark,
W. E., and Durham, U. D., eds.), pp. 341-384. University Presses of Florida, Gainesville,
PL, 1979.