Analysing Temporal Trends in the Ratios of PM2.5/PM10 in the UK

The size of atmospheric Particulate Matter (PM) is important as a determining factor for how long the particle stays in the atmosphere, and where it deposits in the human respiratory tract. Therefore, it is important to analyse PM2.5/PM10 ratios as an indicator of the fine particles and determine how the ratios vary both in space and time. This study uses the most recent 5 years (2010-2014) PM2.5 and PM10 data (mu g m(-3)) from 46 monitoring stations, which are part of the UK Automatic Urban and Rural Network (AURN). In this paper mostly robust statistics, which are not sensitive to non-normal distributions and to extreme values in both tails of the distributions are applied to assess temporal trends in PM2.5, PM10 and their ratios. PM2.5/PM10 ratios demonstrated considerable temporal and spatial variability in the UK and 5 years median ranged from 0.4 to 0.8, resulting in overall median of 0.65. Theil-Sen temporal trend analysis showed that PM2.5/PM10 ratios have increased at several monitoring sites in the UK despite the fact that both PM2.5 and PM10 levels have predominantly decreased. However, trend in PM2.5/PM10 ratios averaged over the 46 monitoring sites was insignificant. Trends in the ratios of PM2.5/PM10 varied during different seasons: spring showed positive significant trend and winter showed negative significant trend, whereas trends in autumn and summer were insignificant. For further investigations: (a) Trends are adjusted for meteorological effect; (b) The emissions of PM10 and PM2.5 (kilotonnes year(-1)) and their ratios from 1990 to 2013 are analysed; (c) Temporal trends of the secondary particles (nitrate and sulphate) are analysed from 2000 to 2014; and (d) The diurnal, weekly and annual cycles in the ratios of PM2.5 and PM10 are analysed.