The meteorological control on the anthropogenic ion content of precipitation at three sites in the UK: The utility of lamb weather types

Daily observations of concentrations of non‐marine sulphate, nitrate, ammonium, and hydrogen ion in precipitation at three sites in the UK (south‐west England, eastern England, southern Scotland) have been used to attribute proportions of the total annual depositions of these ions to various Lamb Weather Types (LWTs). The LWT classification is a convenient description of the daily atmospheric circulation over the British Isles. In terms of affecting the annual character of total annual deposition of the ions, it is Cyclonic, Westerly, and Anticyclonic weather types that play the dominant roles. These roles vary from station to station. Other LWTs can also play important roles, but there is much site‐to‐site and year‐to‐year variation. The patterns of the relationships for each of the stations are explained in terms of the ‘average’ back‐trajectories from each station for precipitation events associated with each of the major LWTs. It is the relative dispositions of these average trajectories with respect to the major pollutant source regions that allows the use of LWTs as simple tools in the interpretation of precipitation composition. There are indications that atmospheric circulation changes may play a part in the variations of precipitation composition over years to decades.