Intraurban variability of PM10 and PM2.5 in an Eastern Mediterranean city

The results of the first large scale chemical characterization of PM10 and PM2.5 at three different sites in the urban city of Beirut, Lebanon, are presented. Between May 2009 and April 2010 a total of 304 PM10 and PM2.5 samples were collected by sampling every sixth day at three different sites in Beirut. Observed mass concentrations varied between 19.7 and 521.2 μg m− 3 for PM10 and between 8.4 and 72.2 μg m− 3 for PM2.5, respectively. Inorganic concentrations accounted for 29.7–35.6 μg m− 3 and 46.0–53.5 μg m− 3 of the total mass of PM10 and PM2.5, respectively. Intra-city temporal and spatial variations were assessed based on the study of three factors: correlation coefficients (R) for PM and chemical components, coefficient of divergence (CODs), and source apportionment using positive matrix factorization (PMF). Based on R and COD of PM concentrations, the three sites appear homogeneous. However, when individual elements were compared, heterogeneity among sites was found. This latter was attributed to the variability in the percent contribution of biogenic and local anthropogenic source factors such as traffic related sources and dust resuspension. Other factors included the proximity to the Mediterranean sea, the population density and the topographical structure of the city. Hence, despite its small size (20.8 km2), one PM monitoring site does not reflect an accurate PM level in Beirut.

Research highlights
► High PM mass concentrations were observed over three monitoring sites in Beirut.
► PMs are both local and regional in nature.
► Overall PM10 and PM2.5 mass concentrations were relatively homogeneous.
► Heterogeneity of PM chemical composition was attributed to various physical and chemical factors.