Abstract
There is a high interest in quantifying temporal trends of air pollutant concentrations as they serve to assess the effects of emission control strategies. In this paper temporal trends (1997-2012) in air pollutant concentrations in the City of Makkah, near the Holy Mosque, have been assessed with the help of Theil-Sen approach and changepoint analysis, which are applicable to both normal and non-normal distributed data and are therefore preferred over classic parametric statistics. Trend analysis of nitrogen oxides (NOx), nitric oxide (NO), nitrogen dioxide (NO2), carbon monoxide (CO), sulphur dioxide (SO2), particulate matter with aerodynamic diameter of 10 micron or less (PM10) and ozone (O-3) was performed, not only at mean concentrations but also at several selected quantiles (minimum, first quartile, median, third quartile and maximum). Trends were positive in SO2, NO2, PM10 and ozone and negative in CO and NO concentrations. NOx (negative) and NO2 (positive) trends were predominantly nonsignificant, however other pollutants showed mostly significant trends. Trends vary at various metrics suggesting different behaviour of air pollutants at various quantiles of the distributions. Changepoint analysis was performed, which provides further insight into the temporal trends and highlights the points when the trends have changed significantly. Potential factors responsible for the observed temporal trends are discussed. Further work on source apportionment of various emission sources and spatial variability of air pollutants is required to provide further insight into the causes behind the trends of air pollutants and help better manage air pollutant levels in Makkah and elsewhere in the country. (C) 2013 Elsevier Ltd. All rights reserved.