SO2 in Beirut : air quality implication and effects of local emissions and long range transport
Résumé
While sulfur dioxide (SO2) emissions have been dramatically restricted in the past few decades, some cities in developing countries still encounter high pollution levels. This makes it essential to implement an air quality monitoring network in these sensitive regions. Results from a program of measuring ground-level concentration of SO2 (from December 2004 till July 2006) at 22 curbside and background sites within the city of Beirut (Lebanon) are presented for the first time. Four-week sampling period measurements were made over 20 periods for all sites by passive sampling. Low SO2 concentrations were observed (3.1 parts per billion on average for the whole period). This value is among the lowest observed in urban areas worldwide. Thus, Beirut is not polluted by SO2 on an annual basis. Highest concentrations were measured in winter time, resulting from low height of the boundary layer and higher emissions of SO2 (e.g., heating). Cluster analysis revealed two different SO2 variation patterns over the city (high- and low-level patterns), highlighting the effects of local sources location and wind direction variability on SO2 distribution. Analysis of seasonal variations pointed out a springtime SO2 maximum in 2005. Beside local sources, long-range transport can account for an important source of SO2 in Beirut, explaining around 50% of SO2 levels within the city.