Visibility trends in the UK 1950–1997

Visibility data have been examined for eight UK Meteorological Office surface network sites. Trends from 1950 to 1997 have been constructed using four different statistical methods; ridit analysis, cumulative percentiles, frequency of “very good” visibility and annual and seasonal means. Improvements in visibility have been experienced at the majority of the sites studied. Major improvements can be observed at many of the sites after 1973 and this is attributed to changes in personal behaviour, fuel use and vehicle fleet efficiency during the 1970s and especially after the 1973 oil crisis. Improvements in visibility at the Scottish sites studied are much less than at the other sites due to their locations in less populated and less polluted areas. Aldergrove, near Belfast in Northern Ireland, has also experienced less improvement in the visibility distance than the other sites.