The spatial and temporal variation of acidic precipitation in Newfoundland: from source to receptor

Abstract

In 1981 between the months of July and December precipitation event samples were s collected at the sites of St. John's, Cape Broyle, Bishop's Falls, Grand Lake, Norris Point, Salmon Dam and Godaleich Pond on the island of Newfoundland in order to determine the acidity of precipitation on the island. -- The samples were analyzed for pH, conductivity, sulphate, nitrate, ammonium, chloride, sodium, potassium, magnesium and calcium. Those samples which were obviously contaminated were discarded which left 60 samples in total. For these accompanying meteorological conditions were determined, namely weather type (i.e. history of the appropriate low pressure track), trajectory sector (from determination of 850 mbar. back-trajectories), antecedent rainfall duration, rainfall total and rainfall intensity. The combination of rainfall totals and precipitation chemistry results enabled the calculation of deposition values of SO⁼₄, NO⁻₃ and H⁺ --factors considered most important with respect to precipitation acidity. From these results the influence of meteorological variables was determined from subjective and objective analyses in the form of basic and multiple correlation. -- Although in a study of precipitation chemistry variability this sampling period was too short to negate the effects of natural variability, certain patterns did emerge which appear to result from the influence of specific variables. Antecedent rainfall duration, weather type and trajectory sector were the most influential variables on precipitation chemistry, although it is difficult to separate them since they are interdependent to a large extent. The most acidic events both in chemical concentration and total deposition of SO⁼₄, NO⁻₃ and H⁺ were associated with lows that had arrived over the island via Labrador and Quebec. Trajectory Sector 2, which includes high emission areas north of the Great Lakes contained the most acidic events with respect to concentrations (SO⁼₄ 1.66 mg.1⁻¹, NO⁻₃ 0.66 mg.1⁻¹, pH 4.55). However, Sectors 4 (41.6% H⁺) and 3 (31.3% H⁺) respectively, produced the highest overall deposition values due to the frequency of trajectories from those sectors. -- Other possible factors influencing precipitation chemistry were site location with respect to local pollution at St. John's, variations in total rainfall receipt (affecting dilution of pollutants) and induced orographic precipitation. In addition, seasonal variations for example summer anticyclonic conditions being most conducive to pollutant accumulation and spring being the season of least precipitation and therefore least dilution. It was not possible to determine if precipitation in Newfoundland is becoming more acidic due to the lack of long-term precipitation records. In fact, CANSAP data from 1977-81 indicate that 1981 concentration values of SO⁼₄ and NO⁻₃ may be lower than usual due to higher precipitation totals.