TEMPORAL AND SPATIAL VARIATIONS OF PM(2.5) AND PM(10) AEROSOL IN THE SOUTHERN CALIFORNIA AIR-QUALITY STUDY

During the summer and fall of 1987, the Southern California Air Qualit y Study (SCAQS) was conducted at more than 40 locations to acquire a d atabase with meteorological, air quality, and visibility measurements, and to assess the causes of elevated ozone and suspended particulate matter concentrations throughout metropolitan Los Angeles, CA (the Sou th Coast Air Basin-SoCAB). PM(2.5) and PM(10) (particles with aerodyna mic diameters equal to or less than 2.5 and 10 mu m, respectively) mas s, elements, water-soluble chloride, nitrate, sulfate, ammonium ions, organic and elemental carbon as well as gaseous ammonia, nitric acid, and sulfur dioxide were measured on eleven episode days during the sum mer and six episode days during the fall. This paper examines the stat istical, temporal, and spatial distributions of the SCAQS aerosol meas urements. PM(2.5) constituted one-half to two-thirds of PM(10) at all sampling sites. PM(10) mass concentrations were highest during the fal l and were dominated by PM(2.5). Nitrate, sulfate, ammonium, and organ ic and elemental carbon were the most abundant species in the PM(2.5) fraction. The coarse particle (PM(10) minus PM(2.5)) fraction was enri ched with soil-related elements (e.g. aluminum, silicon, calcium, iron ) at the inland sites and with marine-related elements (e.g. sodium, c hloride) at the coastal sites. Average concentrations for most chemica l compounds were higher during the fall than during the summer, except for sulfate which was more abundant during the summer. PM(2.5) nitrat e and ammonium concentrations were negatively biased for daytime sampl es with respect to nighttime samples, consistent with diurnal changes in temperature and the effect of these changes on the equilibrium betw een particulate ammonium nitrate and gaseous ammonia and nitric acid. Highest sulfur dioxide concentrations were found at the Long Beach sit e, the location closest to SoCAB oil refineries and ship traffic; and highest ammonia concentrations were found at the Rubidoux site, a loca tion downwind of dairies and agricultural operations.