Long-term trends of primary and secondary NO₂ production in the Athens area. Variation of the NO₂/NOx ratio

• Published in: Atmospheric environment (1994) 2011-12, Vol.45 (38), p.6872-6879
• Main Authors: Mavroidis, I, Chaloulakou, A
• Format: Article
• Language: English
• Subjects: Applied sciences; Athens; atmospheric chemistry; Atmospheric pollution; Automobiles; catalysts; Diesel; Diesel fuels; emissions; European Union; Exact sciences and technology; filters; inventories; issues and policy; monitoring; Nitrogen dioxide; oxidation; ozone; photochemical reactions; Policies; pollutants; Pollution; time series analysis; traffic; Trends; Urban areas
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2010.11.006

This paper examines the contribution of primary and secondary NO₂ production in NOx concentrations and offers a comprehensive analysis of the long-term trends of NOx, NO₂ and O₃ concentrations, as well as of the NO₂/NOx ratio, in the Athens urban conurbation. Long-term pollutant concentration time series show that NO₂ concentrations in Athens have decreased since 1987 but at a slower rate than those of NOx, resulting to an increasing NO₂/NOx concentration ratio. However, this increasing trend is much smaller than those observed in urban areas of other European countries. The possible causes of this trend are examined and especially the interaction with ozone and the amount of direct NO₂ traffic emissions. The results indicate that the increasing NO₂/NOx ratio in the Athens area is mainly attributable to an increased secondary formation of NO₂ through photochemical reactions in the atmosphere. More specifically, two different empirical methodologies were applied to examine the primary NO₂ concentration fraction in Athens, using ambient monitoring data from a kerbside station. Both methods indicate that the primary NO₂ concentration share has not altered significantly between 1998 and 2006. This is mainly attributed to the fact that in the Athens area diesel passenger cars are not allowed and after-treatment technologies such as particle filters and oxidation catalysts are not yet applied in Greece. A probable future penetration of diesel passenger cars in Athens should be combined with inventories of primary NO₂ emissions and with the development of appropriate policies to reduce ambient NO₂ concentrations below the EU limit values.