Meteorological characteristics of large acidic deposition events at Kejimkujik,Nova Scotia

The characteristics of acidic deposition at Kejimkujik National Park, a rural site in south-central Nova Scotia, were determined for the period from May 1979 to December 1983. The acidifying pollutants investigated were H⁺, sulphate ion and nitrate ion. Thirty per cent of the total annual amount of acidifying pollutants deposited by precipitation at Kejimkujik was deposited by only about 8% of the precipitation events during the year. These occasions of large deposition are referred to as episodes and occurred, on average, about five times per year, usually between March and November. The precipitation events that produced episodes were almost always rain events. The major meteorological feature producing deposition episodes at Kejimkujik is the sequence of a large high pressure area from mid-continent moving south of Nova Scotia, producing a prolonged southwesterly to westerly flow over the site, and then a weak frontal system, usually from south of the Great Lakes region, bringing moderate amounts of precipitation to the site. Since deposition episodes were almost always preceded by the above sequence of events, the ability to predict episodes was investigated. The results indicate that many “false alarms” could be anticipated because this sequence also occurs for non-episodes.