Characterizing Sources of PM2.5 in the Middle Eastern Region

Numerous studies have shown that airborne particulate matter (PM) has a potential to affect climate and hydrological cycles. On local spatial scales and especially in urban environments, aerosol particles deteriorate visibility and have adverse effects on human health, including increased risk of premature mortality, hospital admissions, and higher rates of adverse respiratory health indicators in children. Better understanding of these aerosol effects requires detailed information on how aerosol particles originating from different sources are distributed in the atmosphere and how the chemical and physical properties of the particles vary from location to location.

Most of the studies examining air pollution exposures have been conducted in the U.S. and Western Europe, where standards for emissions and ambient air quality have been largely successful in reducing average outdoor pollution levels.  Regulation of air pollution in the Middle East region is, at best, in its initial stages, with air pollutant concentrations that are typically higher than Europe and North America. High levels of PM pollution are also expected to be substantially higher in this region with limited information about their chemical composition.  To date, no studies have been conducted in the Middle East to examine annual trends of PM2.5 composition across the region.

The Middle East Consortium for Aerosol Research Study (MECARS) was conducted between January through December 2007 to provide data for the investigation of the sources and chemical speciation of fine particulate matter (PM2.5) in Palestine, Jordan and Israel. The 24-h PM2.5 samples (particles with an aerodynamic diameter of 2.5 μm or less) were taken at 6-day intervals at eleven urban and rural sites simultaneously. The concentrations and characteristics of the major components in ambient fine particles were measured and evaluated. Chemical analyses were conducted to characterized particulate elemental composition, water-soluble ions, and organic and elemental carbon. PM2.5 mass concentrations exhibited strong monthly variation across the 11 sites, with the maximum difference occurring in May and November. Seasonal variation of PM2.5 concentrations was significant, with higher concentrations (33.9 μgm−3) in the summer (April–September) months. Spring was clearly impacted by dust storms. Measured species accounted for 87% of the total observed mass. Carbonaceous species were the most abundant components, constituting about 40.9% of the total PM2.5 mass concentrations at the different sites. Crustal components averaged 18.2% of the PM2.5 mass.  Sulphate, ammonium and nitrate were three major ions, accounting for 16.2%, 6.4% and 3.8%, respectively, of the total mass of inorganic water-soluble ions. Across the three countries, the daily average PM2..5 concentration levels were in the 3.0–16.2 μgm−3 range, with an multi-site annual average of 28.5 μgm−3.  All sites were above the U.S. Environmental Pollution Agency annual average limit daily limit (15 μgm−3) for total PM2.5.


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