COMPARISON OF AEROSOL ACIDITY IN URBAN AND SEMIRURAL ENVIRONMENTS

During the summer of 1990 acid aerosol measurements were conducted sim ultaneously in Pittsburgh, Uniontown, and State College, Pennsylvania. Acid aerosols and ammonia concentrations were compared at these citie s. Aerosol acidity was found to be lower in the urban area (Pittsburgh ) than the semi-rural areas. Ammonia levels were higher at the urban s ite than in the semi-rural environments, probably due to the higher po pulation density at the urban site. During acid episodes, the dominati ng sulfur species in Pittsburgh were found to be a mixture of totally and partially neutralized sulfates, i.e. (NH4)(2)SO4 and NH4HSO4, whil e in State College and Uniontown sulfur species were primarily a mixtu re of NH4HSO4 and H2SO4. Diurnal variation was found for H+ and SO42- while NH3 exhibited no diurnal pattern. High spatial correlations were found for SO42- levels between Pittsburgh and the semi-rural areas, i mplying a regional transport. In spite of the significant absolute dif ferences, H+ concentrations also were found to be significantly correl ated across sites, as well as with each other at individual sites.