Methods for Measuring Photochemical Air Pollution in Forest Areas

Wien

1971

S. 57-70

3 Abb., 2 Tab., 30 Lit. Ang.

Unselbständiges Werk

200031943

Ambient air contains a tnixture of oxidizing and reducing compounds among which are ozone, nitrogen dioxide, peroxyacetyl nitrate, and sulphur dioxide. The concentrations of these compounds can vary within quite wide limits from 0 to over 100 pphm. An accepted general definition for total oxidants in the air would be a compound that will oxidize a reference material which Is not capable of being oxidized by atmospheric oxygen. Accordingly methods for measuring for measuring atmospheric oxidants consist of exposing an oxidizable substrance to a sample of ambient air and determining the degree of oxidation which has occurred. Two of the most widely used methods of determining the degree of oxidation are colorimetric and coulometric analysis of the iodine released from a potassium iodide solution. Since one mole of ozone theoretically liberates one mole of lodine from this solution, the iodine measured is directly related to the concentration of ozone. Reducing compounds in air have an opposite effect on the reference material by causing a decrease in the degree of oxidation observed. Field equipment to measure atmospheric oxidants consists of continuous automatic instruments and recorders. Sulphur dioxide is scrubbed from the incoming ambient air by suitable chemical compounds. In remote areas specially compounded rubber to which antioxidants have not been added have proved useful to evaluate atmospheric oxidants. Field investigations to determine background concentrations of photochemical air pollutants have been carried out in forests in both Canada and the United States, and the monitoring data are provided. The relationship between these air analyses data and effects on forest trees is discussed.