Formic and acetic acids in coastal North Carolina rainwater

Analyses of rainwater at Wilmington, N.C., for 3 years beginning in October 1987 showed that formic and acetic acids contributed 23 per cent of the acidity. The concentrations of the acids always correlated with each other, but varied with the season and with the origin of the rain. They were highest during local thunderstorms and least in maritime rain. Although the acids were considered primarily natural in origin, concentrations in continental rain were highly correlated with hydrogen ion, nitrate and non-sea salt sulphate, whose origins were principally anthropogenic. This suggested different origins for marine and continental rains. Using the data for formic and acetic acids together with estimates of natural production of nitric and sulphuric acids enabled the background pH of uncontaminated rain to be assessed as 4.9; this agreed with the results of other investigators. There are 43 references.