Data available from the ongoing SouthEastern Aerosols Research and CHaracterization Study (SEARCH) and concurrent monitoring programs provide a basis for beginning to examine the relationships between aerosols and other geographical and meteorological factors that influence the phenomenon of regional haze in the southeastern U.S. The SEARCH data are available for eight monitoring sites located throughout the Southeast (in urban, suburban, and rural locations). Daily (24-hour) measurements of particles, trace gasses, and meteorological parameters from the SEARCH monitoring network are available for a one-year period beginning in January 1999. Measurements of particles include speciated particulate matter with diameters of less than 2.5 microns (PM2.5) and between 2.5 and 10 microns (PMCOARSE). Trace gas measurements include ozone, oxides of nitrogen (NO, NOx), NOy, carbon monoxide (CO), and sulfur dioxide (SO2). Meteorological parameters include wind speed and direction, temperature, relative humidity, pressure, solar radiation, and rainfall.

This paper describes the use of the SEARCH data to explore the relationships between aerosol formation, composition, and transport and meteorology. These findings are then used to guide the development of recommendations for selecting discrete modeling episode periods for air quality modeling applications, with consideration of the frequency and magnitude of measured PM2.5 events, observed variations in the relative importance of the PM constituents, the type and range of important PM-related processes, the geographical scales encompassed by both urban-health and regional-haze issues, and potential interactions with ozone and other pollutants. The emphasis of the analysis is PM2.5 and regional haze.

The episode selection procedures are then used to construct a set of episode days for regional-scale modeling of the Southeast that will provide the basis for a meaningful model application and attainment demonstration for PM2.5 and visibility.