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This study reports for the first time a time series analysis of daily urban air pollutant levels (CO, NO, NO2, O3, PM10, and SO2) in Beirut, Lebanon. The study examines data obtained between September 2005 and July 2006, and their descriptive analysis shows long-term variations of daily levels of air pollution concentrations. Strong persistence of these daily levels is identified in the time series using an autocorrelation function, except for SO2. Time series of standardized residual values (SRVs) are also calculated to compare fluctuations of the time series with different levels. Time series plots of the SRVs indicate that NO and NO2 had similar temporal fluctuations. However, NO2 and O3 had opposite temporal fluctuations, attributable to weather conditions and the accumulation of vehicular emissions. The effects of both desert dust storms and airborne particulate matter resulting from the Lebanon War in July 2006 are also discernible in the SRV plots.

While sulfur dioxide (SO 2 ) 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 groundlevel concentration of SO 2 (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 SO 2 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 SO 2 on an annual basis. Highest concentrations were measured in winter time, resulting from low height of the boundary layer and higher emissions of SO 2 (e.g., heating). Cluster analysis revealed two different SO 2 variation patterns over the city (high-and low-level patterns), highlighting the effects of local sources location and wind direction variability on SO 2 distribution. Analysis of seasonal variations pointed out a springtime SO 2 maximum in 2005. Beside local sources, long-range transport can account for an important source of SO 2 in Beirut, explaining around 50% of SO 2 levels within the city.