ATMOSPHERIC MONITORING

26.1. ATMOSPHERIC MONITORING

Good analytical methodology, particularly that applicable to automated analysis and continuous monitoring, is essential to the study and alleviation of air pollution. The atmosphere is a particularly difficult analytical system because of the very low levels of substances to be analyzed; sharp variations in pollutant level with time and location; differences in temperature and humidity; and difficulties encountered in reaching desired sampling points, particularly those substantially above the earth’s surface. Furthermore, although improved techniques for the analysis of air pollutants are continually being developed, a need still exists for new analytical methodology and the improvement of existing methodology.

Much of the earlier data on air pollutant levels were unreliable as a result of inadequate analysis and sampling methods. An atmospheric pollutant analysis method does not have to give the actual value to be useful. One which gives a relative value may still be helpful in establishing trends in pollutants levels, determining pollutant effects, and locating pollution sources. Such methods may continue to be used while others are being developed.

Air Pollutants Measured

The air pollutants generally measured may be placed in several different categories. In the U.S., one such category contains materials for which ambient (surrounding atmosphere) standards have been set by the Environmental Protection Agency. These are sulfur dioxide, carbon monoxide, nitrogen dioxide, nonmethane hydrocarbons, and particulate matter. The standards are categorized as primary and secondary. Primary standards are those defining the level of air quality necessary to protect public health. Secondary standards are designed to provide protection against known or expected adverse effects of air pollutants, particularly upon materials, vegetation, and animals. Another group of air pollutants to be measured consists of those known to be specifically hazardous to human health, such as asbestos, beryl- The air pollutants generally measured may be placed in several different categories. In the U.S., one such category contains materials for which ambient (surrounding atmosphere) standards have been set by the Environmental Protection Agency. These are sulfur dioxide, carbon monoxide, nitrogen dioxide, nonmethane hydrocarbons, and particulate matter. The standards are categorized as primary and secondary. Primary standards are those defining the level of air quality necessary to protect public health. Secondary standards are designed to provide protection against known or expected adverse effects of air pollutants, particularly upon materials, vegetation, and animals. Another group of air pollutants to be measured consists of those known to be specifically hazardous to human health, such as asbestos, beryl-

emissions, acid (H 2 SO 4 ) mist, particulate matter, nitrogen oxides, and sulfur oxides. These substances often must be monitored in the stack to ensure that emissions standards are being met. A fourth category consists of the emissions of mobile sources (motor vehicles)—hydrocarbons, CO, and NOx. A fifth group consists of miscellaneous elements and compounds, such as certain heavy metals, fluoride, chlorine, phosphorus, polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls, odorous compounds, reactive organic compounds, and radionuclides.

Much of the remainder of this chapter is devoted to a discussion of the analytical methods for most of the species mentioned above. For some species, an analytical method is well developed and reasonably satisfactory. For others, improved methods would be useful. The development of analytical techniques for air pollutants is a very active area of research and development in analytical chemistry.

The units in which air pollutants and air-quality parameters are expressed include for gases and vapors, µg/m 3 (alternatively, ppm by volume); for weight of particulate matter, µg/m 3 ; for particulate matter count, number per cubic meter; for visibility, kilometers; for instantaneous light transmission, percentage of light transmitted; for emission and sampling rates, m 3 /min; for pressure, mm Hg; and for temperature, degrees Celsius. Air volumes should be converted to conditions of 10˚C and 760 mm Hg (1 atm), assuming ideal gas behavior.