STATISTICAL SUMMARY AND ANALYSES OF EVENT PRECIPITATION CHEMISTRY FROM THE MAP3S NETWORK, 1976-1983

The MAP3S precipitation chemistry network base of event chemistry data includes nine sites widely distributed over the northeastern quadrant of the USA. Eight of these sites now have a period of record of at least 5 years. Four species (total sulfur, .**GRAPHIC**. H+ and .**GRAPHIC**. account for the bulk of ionic equivalents at seven island sites; Ca2+ is nearly as important as .**GRAPHIC**. at several of the inland sites, and sea salt species are major components at the two coastal sites. Average pH values (from arithmetic mean H+) range from 4.03 to 4.24 over the network. Time trend analyses for the period for sulfur and H+ show a consistent decrease, but the decrease is quite small and has low statistical significance; .**GRAPHIC**. and .**GRAPHIC**. show similar though less consistent trends. Significant seasonal trends (summer maximum, winter minimum) are found at most sites for sulfur and .**GRAPHIC**. has a much weaker seasonal trend except at the coastal sites. Species pair correlations are strong among the four major ions, with the exception of correlations involving H+ at sites where crustal species are more important (Illinois, Ohio). Correlations can qualitatively be explained by common sources (crustal, sea-salt, anthropogenic), polluted vs nonpolluted events, and strong seasonal trends.