EVALUATION OF FILTER-BASED AEROSOL MEASUREMENTS DURING THE 1987 SOUTHERN CALIFORNIA AIR-QUALITY STUDY

The Southern California Air Quality Study (SCAQS) was conducted during the summer and fall of 1987 to assess the causes of elevated ozone an d suspended particulate matter concentrations in California's South Co ast Air Basin (SoCAB). Extensive gaseous (i.e. nitric acid, ammonia, s ulfur dioxide) and particle (i.e. PM2.5 and PM10 mass, elements, ions, carbon) measurements were acquired for 11 days during the summer at n ine locations, and six days during the fall at six locations. Outliers were identified so that they could be excluded from further statistic al analyses. Carbon and elemental measurements were found to be negati vely biased by approximately 20% owing to inhomogeneous aerosol deposi ts on the SCAQS filters and analysis methods which were applied to a p ortion of the filters. These biases seem relatively consistent, howeve r, and should not affect conclusions drawn from data analysis efforts if they are appropriately considered. Significant fractions (30-60%) o f ammonium nitrate volatilized during the summer when temperatures wer e higher. Less than 10% typically volatilized during the fall when tem peratures were lower. Anion/cation balances support the accuracy and p recision estimates of the nitrate, sulfate, and ammonium measurements. Coarse particle sulfate was generally low, while coarse particle nitr ate was most pronounced at the coastal sites. This paper documents SCA QS filter-based aerosol measurement methods, and evaluates the accurac y, precision, and validity of the data set. Various comparisons were m ade for: (1) PM2.5/PM10 ratios for mass and major chemical species; (2 ) sum of chemical species versus measured mass; (3) sulfate versus sul fur ratios; (4) PM2.5 particulate nitrate versus nitric acid-denuded n itrate; and (5) anion/cation balances. The measurement and evaluation techniques presented in this paper serve as a guideline for other data analysis and modeling studies.