Monitoring Acid Rain

The simplest way to monitor the acidity of acid rain (from wet deposition) is to collect rain samples and to measure the pH of the water. Since 1987, such monitoring of acid rain has taken place in and around Greater Manchester in the UK, the Greater Manchester Acid Deposition Survey (GMADS). Rain collectors have been sited in Greater Manchester following strict criteria. The collectors must be 100m away from small point sources (such as domestic chimneys), 100m from small mobile sources (road traffic), 1km from major roads, 5km from large surface works, and 10km from large point sources (such as power stations).

Across the UK, the Acid Deposition Monitoring Network monitors the composition and acidity of precipitation at 32 sites to provide an accurate measurement of pollutant deposition in rain and snow to assist in implementing a critical loads approach to environmental protection. All precipitation samples are analysed for conductivity, pH, sulphate, nitrate and chloride concentration, and a variety of metal ions (ammonium, sodium, calcium, potassium, and magnesium). Combining these measurements of acid deposition with the estimated critical loads in the form of maps can highlight those areas where the tolerance to acidity is being exceeded, and where damage from acidification is most likely to be found.