Characterizing temporal variability of PM2.5/PM10 ratio and its relationship with meteorological parameters in Bahrain

The Kingdom of Bahrain is ranked in the top 10 most urban ambient air polluted countries in the world due to high particulate matter (PM) concentrations. The main objective of this article is to analyze comprehensively long-term temporal (annual, seasonal, and monthly) trends of PM2.5/PM10 ratios using PM data collected simultaneously from five governorates in Bahrain over six years (2006-2012) by employing state-of-the-art Theil-Sen approach. Results showed the calculated mean PM2.5/PM10 ratio was 0.31 suggesting coarse particulates are the dominant source of PM pollution. Both observed and adjusted temporal trend of PM2.5/PM10 ratios showed significant decrease during the study period. Mean trend analysis of PM2.5/PM10 ratio also showed that it has decreased in all seasons. Annual cycle of PM2.5/PM10 ratio showed that the lowest ratio was observed in April while the highest ratio was witnessed in September. Weekly and diurnal trends of PM2.5/PM10 ratio were investigated using hourly data of PM10 and PM2.5 recorded in 2012. Temporal variation of PM2.5/PM10 ratio did not exhibit any distinctive trend on weekly and diurnal analysis. Correlation analysis showed positive association between PM2.5 and PM10 (r=0.77) and PM2.5/PM10 ratio exhibited negative association with temperature and wind speed suggesting PM10 concentrations increase in high ambient temperatures and windy days. Bivariate polar plot analysis of PM data together with meteorological parameters demonstrated that sources of PM are primarily located in the west and north-west direction thus identifying surrounding deserts as major contributors to PM pollution.