Concentration measurements and chemical composition of PM10-2.5 and PM2.5 at a coastal site in Beirut, Lebanon

Abstract

Emission measurements and chemical profiles of PM10-2.5 (coarse) and PM2.5 (fine) in Lebanon are reported for the months of February till May of 2003. A 4 month average of 76 μg m−3 for PM10-2.5 and 40 μg m−3 for PM2.5 compared well with East Mediterranean cities but was higher than most emission measurements reported for the West Mediterranean basin. Using the ATR–FTIR technique, the chemical composition of aerosols was identified. Inorganic ions such as SO42−, NO3−, SiO42−, CO32−, and NH4+, showed higher concentrations of PM2.5 when compared to PM10-2.5. Organic functional groups like aliphatic carbons, alcohols, carbonyls, and organic nitrates were also detected. Higher concentrations of organic species, i.e. aliphatic hydrocarbons and long chains of alcoholic and carboxylic acid substances, were identified in PM2.5 while in PM10-2.5, higher water concentrations were observed. Comparison between the ATR spectra of samples collected on a “regular” and a “sandy” day clearly showed the increase of SiO42− ions and calcium carbonate during the sand storm due to dust loading on the Teflon filters. This study is one of the few works that have reported emission measurements in the Eastern Mediterranean, complementing thereby the large amount of data available in the Western Mediterranean. More importantly, this paper establishes a comparison between the main constituents of PM10-2.5 and PM2.5 using ATR-infrared spectroscopy, for the first time. Understanding the composition of different aerosol size fractions in the atmosphere enables us to better predict detailed chemical environmental variations.