Statistical approach for the characterization of NO2 concentrations in Beirut.
Résumé
Measurement of ambient NO2 concentrations using diffusion tube samplers is widespread in many countries. Results from a program of measuring ground-level concentration of NO2 at 20 urban sites within the city of Beirut are presented. In addition, two curbside sites were implemented at different heights. Two-week sampling period measurements were performed over 41 periods for all sites. A study of the sites' behaviors was conducted using principal component analysis and agglomerative hierarchical clustering. Firstly, results indicate that urban sites are equivalent, and one global class is identified. Any further monitoring of the nitrogen dioxide concentration can be conducted by decreasing the number of urban sites. Secondly, nitrogen dioxide concentration levels present a seasonal variation, as expected. Maximum average concentration of 178 μg m − 3 was observed during winter (December 2005) and a minimum concentration of 17 μg m − 3 was observed during summer (May 2006). The annual average concentration measured in 2005 is 67 μg m − 3, while the recommended value from the World Health Organization is 40 μg m − 3.