SPATIAL AND SEASONAL TRENDS IN PARTICLE CONCENTRATION AND OPTICAL EXTINCTION IN THE UNITED-STATES

In the spring of 1988 an interagency consortium of Federal Land Manage rs and the Environmental Protection Agency initiated a national visibi lity and aerosol monitoring network to track spatial and temporal tren ds of visibility and visibility-reducing particles. The monitoring net work consists of 36 stations located mostly in the western United Stat es. The major visibility-reducing aerosol species, sulfates, nitrates, organics, light-absorbing carbon, and wind-blown dust are monitored a s well as light scattering and extinction. Sulfates and organics are r esponsible for most of the extinction at most locations throughout the United States, while at sites in southern California nitrates are dom inant. In the eastern United States, sulfates contribute to about two thirds of the extinction. In almost all cases, extinction and the majo r aerosol types are highest in the summer and lowest during the winter months.