Seasonal and Spatial Patterns of Air Pollution in Los Angeles County Warren R. Bland" ABUNDANT DATA are becoming available on the chemistry¦ and meteorology of air pollution,1 as well as its associated human problems. It remains to put these data to work in the interests of sound land use and the better life in general. Household and government policy decisions, for example, may be facilitated by better knowledge of spatial variations in air quality , expressed in ways which can be readily visualized and applied. The significant pollution problem that prevails in the Los Angeles area has prompted voluminous collection of data, which reveal considerable local variation in contaminants by intensity, type, and timing. Portrayal of spatial variations in pollutants within this metropolitan area is therefore seen as a useful and feasible objective. In the present paper the writer summarizes air quality by developing and mapping an air pollution index * Dr. Bland is Associate Professor of Geography at California State University, Northridge 91324. 1 See, for example, Philip A. Leighton, Photochemistry of Air Pollution (New York: Academic Press, 1961). More pertinent to the specific locale of the present paper are James C. Edinger, The Meteorology of Los Angeles' Polluted Layer (Los Angeles: University of California, Department of Meteorology, January 1958) and James C. Edinger et al., "Penetration and Duration of Oxidant Air Pollution in the South Coast Air Basin of California," Journal of the Air Pollution Control Association, Vol. 22, No. 11 (November 1972), pp. 882-886. 25 26 ASSOCIATION OF PACIFIC COAST GEOGRAPHERS Figure 1. Los Angeles lowland (unshaded), showing monitoring stations of the County Air Pollution Control District. The complete air basin, of which the 1,200-square-mile study area is a part, extends into several adjacent counties. based upon counts of principal atmospheric contaminants in the Los Angeles lowland ( Figure I)." The Air Pollution Index The aerial contaminants that are regularly and widely recorded in the Los Angeles area consist of carbon monoxide ( CO ), sulfur dioxide ( SO.. ), nitrogen oxides ( NOx ),3 and ozone ( O , ) . The latter two pollutants are the most important reactants in photochemical pollution, though carbon monoxide is by far the most abundant quantitatively. All four contaminants, however , are commonly accepted as being physiologically and/or 2 Los Angeles County Air Pollution Control District, Monthly Report of Meteorology, Air Pollution Effects, and Contaminant Maxima, JanuaryDecember , 1970. :l Oxides of nitrogen are the sum of nitrous oxide and nitrogen dioxide. YEARBOOK · VOLUME 36 · 197427 psychophysiological^ impairing, though medical research has not assessed their precise effects or eliminated the possibility of there being greater effects from still-unknown interactions of these or other pollutants.4 The geography of air quality is often portrayed by simply mapping the occurrence of each separate contaminant, but it is difficult to comprehend the overall conditions at specific places from the resulting disparate maps. A summary index system which would integrate data for all relevant pollutants, however, must recognize the appreciable differences in toxicity values of the various pollutants. Failure to do so would, for example, exaggerate the contribution of low-toxicity carbon monoxide to the air pollution problem, while understating the effects of a lower-level, but possibly equally noxious, contaminant such as sulfur dioxide. It was assumed for the present study that the four previously named contaminants are potentially equal health hazards; therefore, their levels of concentration at some critical threshold should be considered functionally equivalent, whatever their relative quantities at that moment. To achieve this end, the method of weighting pollutants that was adopted relies upon their relative concentrations at the threshold values designated by the Los Angeles County Air Pollution Control District for calling first-stage pollution alerts."' These concentrations, expressed in parts per million parts of air, are 50 for carbon monoxide, 3 for sulfur dioxide, 3 for nitrogen oxides, and 0.5 for ozone. If a weight of 1 is assigned to the value of 50 ppm for carbon monoxide, then the corresponding weights for the other stated units are approximately 17 for sulfur dioxide, 17 for nitrogen oxides, and 100 for ozone. To express total atmos- * For a detailed discussion of physiological responses of humans to air pollution, see Wilbert S. Aronow et al...