Analysing PM2.5 and its Association with PM10 and Meteorology in the Arid Climate of Makkah, Saudi Arabia

Atmospheric Particulate Matter (PM) is considered one of the most critical air pollutants in terms of its detrimental health impacts, environmental degradations and visibility. Particles size, their chemical composition and atmospheric levels are important factors for determining their adverse health impacts. In this paper various aspects of PM2.5 are analysed including PM2.5/PM10 ratios and association with meteorological parameters using data collected from January 2014 to September 2015 in Makkah Saudi Arabia. During the study period, mean PM2.5/PM10 ratio was found to be 0.64, whereas median and maximum ratios were 0.69 and 0.99, respectively. Diurnal, weekly and annual cycles of PM10, PM2.5 and their ratios were analysed, which demonstrated considerable variations during various hours of the day, days of the week and months of the year. PM2.5/PM10 ratios were lower in summer (June and July) and higher in winter (November and December), likewise the ratios were lower during afternoon and higher in the morning and evening. As expected, there was a positive correlation between PM10 and PM2.5 (r = 0.51) and both PM10 and PM2.5 showed negative association with relative humidity and positive with wind speed and temperature. Furthermore, PM2.5/PM10 ratios were lower (< 0.45) at lower relative humidity (< 16%) and higher (> 0.70) at higher relative humidity (35-90%), indicating a shift towards high PM2.5 concentrations at higher relative humidity. Polar plots showed lowest ratios at high wind speed (> 3 m s-1) blowing from west and southwest direction in summer, and highest ratios at low wind speed (< 2 m s(-1)) in winter. Polar plots were successfully applied to show the interaction between various meteorological parameters and PM2.5/PM10 ratios. Further work on source apportionment and receptor modelling of PM is required to help develop air quality index and prepare an effective air quality plan for Makkah.