Abstract for presentation at 14th IUAPPA World Congress

The Fresno supersite was established in 1999 to: 1) evaluate new measurement methods; 2) better understand atmospheric processes; and 3) support health effects studies.1 The supersite has now acquired more than six years of data that allows climatological variability to be examined. Major findings are: 1) more than half of the ammonium nitrate evaporates from filter samples during non-winter periods, but more than 90% is recovered during winter; 2) nitrate forms aloft during winter and is moved throughout the central valley, to be mixed to the surface during late morning and early afternoon; 3) organic and elemental carbon are much higher in Fresno than outside the city limits, implying the vehicle exhaust, cooking, and vegetative burning within the city are the major sources; 4) source apportionment using organic markers confirms that urban-scale emissions from exhaust, cooking, and vegetative burning are the major carbon sources; 5) year-to-year variability in PM_2.5 concentrations is large, depending mostly on the frequency between and duration of Pacific storms during the winter. The Fresno supersite has served as a model for other supersites throughout the world, hosting visitors from many different countries. Standard operating procedures and measurement evaluations have been published to facilitate detailed aerosol modeling on a global scale.