The chemistry of bulk precipitation at a site in southeast england—II. Relationships between ions and comparison with other sites

Abstract

This paper contains a statistical analysis of bulk precipitation chemistry of rain falling on the Tillingbourne Catchment, Surrey. Over the years 1978–1981, mean volume-weighted concentrations were: pH, 4.15, 70.8 μeq ℓ −1 H +; organic, 2.8 mg ℓ −1; total SO 2− 4, 80.5 μeq ℓ −1; NO − 3, 36.2 μeq ℓ −1; NH + 4, 40.9 μeq ℓ −1; Cl − (2 years) 97.4 μeq ℓ −1, rainfall 1067mm. Compared to other sites in the U.K. and elsewhere receiving acid precipitation in this pH is at the low end of the range, but levels of the other ions are moderate. Similar relations apply to deposition. Ion concentrations are highly correlated, especially total SO 2− 4, NO − 3 and NH + 4. This group is linked more loosely to pH and organic content, while Cl − does not correlate at all with the other ions, implying a totally different source, probably sea salt. H + ions in rain correlate better with NO − 3 than with SO 2− 4 and regression analysis suggests that almost all the NO − 3 is probably associated with nitric acid, whereas only about 57% of the SO 2− 4 is associated with sulphuric acid. Deposition is approximately related to rainfall by a power law relationship in which the exponent of the equation varies between 0.5 and 0.9. However, it is concluded that an adequate estimate of deposition cannot be obtained from rainfall alone.