Characterizing temporal variability of PM_2.5/PM₁₀ ratio and its relationship with meteorological parameters in Bahrain

Abstract

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 PM_2.5/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 PM_2.5/PM₁₀ ratio was 0.31 suggesting coarse particulates are the dominant source of PM pollution. Both observed and adjusted temporal trend of PM_2.5/PM₁₀ ratios showed significant decrease during the study period. Mean trend analysis of PM_2.5/PM₁₀ ratio also showed that it has decreased in all seasons. Annual cycle of PM_2.5/PM₁₀ ratio showed that the lowest ratio was observed in April while the highest ratio was witnessed in September. Weekly and diurnal trends of PM_2.5/PM₁₀ ratio were investigated using hourly data of PM₁₀ and PM_2.5 recorded in 2012. Temporal variation of PM_2.5/PM₁₀ ratio did not exhibit any distinctive trend on weekly and diurnal analysis. Correlation analysis showed positive association between PM_2.5 and PM₁₀ (r = 0.77) and PM_2.5/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.

Keywords:

• Air pollution
• Arabian Peninsula
• dust events
• particulate matter
• temporal trend
• Theil-Sen estimator

Acknowledgments

The authors are grateful to the Supreme Council for Environment for providing ambient air quality monitoring data. Also, they are thankful to Climate and Observation section in the Meteorological Directorate of Bahrain for providing meteorological data for the study period. We further appreciate valuable comments from anonymous reviewers.

Disclosure statement

No potential conflict of interest was reported by the author(s).