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Soil Absorption of Air Pollutants¹

ABSTRACT

Soil emits some, but absorbs many, air pollutants. The net effect of the soil is to reduce air pollution by absorbing air pollutant gases and particulate matter and converting them into less harmful forms, forms unavailable to plants and nutrients. The gases emitted by soils, such as H₂S, N₂O, CH₄, and CO, are products of reactions largely outside of man's control and are natural parts of the carbon, nitrogen, and sulfur cycles.

Soils absorb organic gases faster and in greater amounts with increasing molecular weight and with increasing number of nitrogen, phosphate, oxygen, sulfur, and other functional groups in the compound. The absorption of lower-molecular weight and less-substituted organic gases depends upon the buildup of an appropriate microbial population.

The absorption of inorganic air pollutants by soils is primarily by chemical and physical means. Many of the air pollutant gases oxidize after being absorbed and produce acidity which is countered by the pH-buffering capacity of the soil.

Soils are also a source and the major absorbent of siliceous particulate matter in air. Heavy metal, fluoride, and other pollutant aerosols are absorbed and rapidly rendered unavailable to plants. The extent of unavailability of most absorbed elements increases with soil pH. The inactivation of heavy metals by soils is approximately Cu > Pb > Zn > Cd > Ni.

Key Words: nickel • cadmium • lead • arsenic • copper • H₂O • N₂O

¹ Journal Paper no. 1880 of the Arizona Agr. Exp. Sta., Tucson. Supported in part by Rockefeller Foundation Grant 70073.

² Associate Professor, Dep. of Soils, Water and Engineering, Univ. of Arizona, Tucson. 85721.

Received for publication January 20, 1972.