Spatial Variations of Acid Precipitation in Southern California

Abstract

Wet-precipitation-only samplers were used to collect acid precipitation at nine sites in the Los Angeles basin of southern California during the 1978-1979 hydrologic year. Concentrations of the major cations (H⁺, NH₄⁺, Na⁺, K⁺, Ca²⁺, and Mg²⁺) and the major anions (Cl⁻, NO₃⁻, and SO₄²⁻) as well as trace species were determined. The relative importances of natural and anthropogenic sources were calculated by a chemical balance. Variations of sea salt, soil dust, NNH₄⁺, SO₄²⁻, and NO₃⁻ contributions agreed with source distributions, scavenging, and advection patterns. The nitrate to non-sea-salt sulfate equivalent ratio varied from 0.4 near coastal stationary sources to 2.8 in rural mountain areas with a precipitation-weighted average ratio of 1.1. Equilibrium models are used to relate the chemical composition of rain water with P_(SO₂), P_(NH₃), P_(NO₂), P_(NO), and P_(HNO₃) during precipitation. Mass-balance calculations indicate that less than 2% of the anthropogenic emissions of NO_x and SO_x in southern California are locally scavenged on an annual basis.

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