Comment on "Ten-Year Ozone Trends in California and Texas''

Abstract

The results of analyses of ozone data from California's South Coast Air Basin (Los Angeles, Orange, Riverside and San Bernardino counties), presented in Ten Year Ozone Trends in California and Texas by H.M. Walker do not agree with the results of similar analyses performed by technical staff of the South Coast Air Quality Management District. There are also several errors and omissions in the article which should be noted. The author has stated that the California State Air Resources Board (ARB) used 20 percent for the conversion of all its data except for the San Diego area. This is not correct. The method in use prior to June 1975 in Los Angeles County was found to be sufficiently comparable to the ultraviolet photometer (UV) calibration method to require no correction. The method in use in the Orange, Riverside, and San Bernardino County areas was found to calibrate high relative to the UV calibration method, and data obtained prior to June of 1975 have been corrected by a factor of 0.80 to make them comparable to later data. In addition, the author has not taken into account the changes in monitoring methods which occurred from 1974-1979 in this Basin. For Losmore » Angeles County locations, the average daily maximum ozone concentration determined by UV photometer averaged 12 percent higher than that measured by continuous potassium iodide (KI) method. While the ARB has corrected data from this area for change in calibration method where required, no correction is made for monitoring method changes.« less