Correction December 2019
A mapping error that affected the underlying ammonia concentration data was detected in December 2019, after the original publication of this dataset August 2019. See Trends Report 2019. The error affected the 2014-2016 mean, but not previous dates. Correcting the error made only a small change in the reported exceedances. At UK and country levels, the biggest change was in Northern Ireland, where the area exceeding the 1 µg m-3 limit was originally calculated as 71.3%. After correction, this area was 70.7 %. However, it does make more difference at some specific locations. The Critical Level exceedance data presented here were corrected and updated on 13th December 2019, and supersede the previously published dataset.