Levels and indoor–outdoor relationships of PM10 and soluble inorganic ions in Beirut, Lebanon

PM10, which is considered among the major indoor and outdoor pollutants, was measured in several residential homes and corresponding outdoor environments in the Great Beirut area over the summer and winter seasons of 2005. Few studies on PM10 levels indoors in Beirut are restricted to short-term periods in public places. In this study, 78 PM10 samples were collected on Teflon filters using an active sampler at a flow rate of 5 L/min. PM10 mass concentrations were determined by gravimetric analysis, and inorganic chemical speciation was carried out using ion chromatography. Outdoors, PM10 elevated mass concentrations correlated well with high traffic density. The observed high intra-site temporal variation (minimum of 34 and a maximum of 120 μg/m3) was attributed to the dynamic air masses passing over the Eastern Mediterranean region. Indoors, PM10 levels were highly affected by outdoor levels, but were enhanced over those of outdoors when smoking activities were recorded. In winter, the overall average outdoor concentration dropped by 19%, whereas the average indoor concentration increased by 50% over the ones calculated for the summer. Ventilation and air exchange rates were found to be approximately equal to unity during summer since most doors and windows remain open. This rate drops to almost half during winter. As for particulate ions namely nitrates and sulfates, the former showed concentrations that are higher than the values reported in the region in both winter and summer seasons, suggesting high emissions from local vehicles. However, SO42− average concentrations were comparable to values reported in other studies conducted in Eastern Mediterranean sites. Soluble particulate nitrates and sulfates exhibited similar indoor and outdoor levels in non-smoking homes (IO ~ 1), but in smoking homes the drop in nitrate concentrations reached around 70%, indicating a high anionic reactivity with tobacco smokes.