Study of chemical characteristics of particulate matter concentrations in Riyadh, Saudi Arabia

Particulate matter samples were collected from several locations during September 2011 and September 2012 in Riyadh, Saudi Arabia. In addition to determining particulate matter (as PM10) concentrations, the samples were analyzed for several metals and ions. PM concentration was approximately 3 times higher than the Country’s ambient air quality standards respectively. Metals and ions contributed to about 21.5% and 16.2% of the PM concentrations respectively. Summer vs. winter comparison showed that PM concentrations were approximately 84% higher in summer and the crustal matter species such as Fe, Mn, Ti, Ca+2, Mg+2 increased several folds in summer, primarily attributed to dust storms. The weekdays PM concentrations were 17% more than the weekend concentrations, indicating weekday activities contribute to the concentrations. The dust storms lead to over 200% increase in the PM and some elements primarily Al, Fe, Mg and Ca. Spatial comparison at industrial and residential locations revealed about 60% increase in PM concentrations and substantial increase in Zn, Mn, B, Mg, Fe, and Al and the ions K+, SO4--, and Cl- at industrial locations. Bivariate correlations among the metals and ions demonstrated that strong correlation existed between Al, Fe, Mg, K and Mn suggesting a common origin for these species i.e. the crustal mineral aerosols. The correlations among cations and anions implied the presence of compounds in the atmosphere such as CaSO4, (NH4)2SO4, KCl, KSO4, and also to some extent MgSO4. An investigation of ionic ratios revealed that ratios SO4-2/NO3-, Ca+2/K+, and Ca+2/Na+ could be possible indicators to identify scenarios industrial over residential locations, storm days over no storm days and summer over winter periods respectively.