Size and composition distribution of atmospheric particles in southern California

Continuous measurements of single particle size and chemical composition in the atmosphere are made using aerosol time-of-flight mass spectrometers (A TOFMS) operated alongside more conventional reference air sampling instrume nts at a network of three urban air monitoring sites in southern California . Electrical aerosol analyzers and optical particle counters are employed t o acquire continuous particle size distribution data, and inertial impactor and bulk filler samples with 4-h resolution are taken for determination of particle size and chemical composition. Filter and impactor samples also a re taken upwind of the air basin at Santa Catalina Island in order to chara cterize background air quality. The airborne particle size and composition distribution as measured by the cascade impactors at inland sites differ fr om that over the ocean principally due to depletion of sea salt particles a ccompanied by the addition of fine carbon-containing particles and secondar y aerosol nitrate. Data from the ATOFMS systems create a continuous time se ries of sodium-, ammonium-, nitrate-, and carbon-containing particle counts that provide a high-resolution view of differences in particle composition as a function of location in the air basin. Results show that the characte ristic peak in the Los Angeles area aerosol mass distribution in the 0.2-0. 3-mu m size range observed during the 1987 SCAQS experiments has been reduc ed, consistent with reductions in diesel soot and elemental carbon emission s since that time.