Rainfall acidity in Northern Britain - exploring the data.

Daily rainfall pH measurements from a site in south Scotland were found to have a bimodal distribution. Similarly, monthly data from a network of bulk rain collectors in northern Britain gave bimodal distributions. Sites with an annual average pH of 4.7 had occasional monthly pH values of pH 4 or less. The annual average pH was a poor indicator of the frequency of such acidic periods, and may not be a good indicator of potential effects. Data from a daily and monthly collector at the same site are compared and the discrepancies discussed. Daily pH measurements gave significantly greater acidities than monthly pH measurements, but these differences were small for months with rain-weighted pH < 5.