Estimates of the sulfate scavenging coefficient from sequential precipitation samples on Long Island

By comparing deposition of sulfate in successive hours of precipitation samples taken over a 6 year period at Brookhaven National Laboratory (BNL) on Long Island in New York, we have estimated scavenging coefficients in air for sulfate under a variety of meteorological and seasonal conditions. The scavenging coefficients obtained are underestimated (typically up to 12%) because of liquid phase production of sulfate from SO₂ scavenged in air. The square root transformation of the scavenging coefficients λ^1/2, yields an approximately normal distribution. An interesting property of the distribution of scavenging coefficients is that the ratios of the mean value of λ^1/2 to its standard deviation cluster around the value 2.4; this property may limit the choice of stochastic models which describe the scavenging process. The mean value of the sulfate scavenging coefficient is 1.0 × 10^-4 s^-1. A trend analysis of the relationship between the scavenging coefficients and rainfall rate indicates that the sulfate scavenging coefficient is virtually invariant for rainfall rates ≤ 5 mm h^-1.