An approach for determining air pollution monitoring sites Enrique González Ferradás a , Marta Doval Miñarro a, * , Isabel María Morales Terrés a , Francisco José Marzal Martínez b a Department of Chemical Engineering, School of Chemistry, University of Murcia, 30071 Murcia, Spain b Department of Thermal and Fluid Engineering, Technical University of Cartagena, 30203 Cartagena, Murcia, Spain article info Article history: Received 9 November 2009 Received in revised form 29 March 2010 Accepted 31 March 2010 Keywords: Benzene Air pollution monitoring sites abstract EC Directive 2008/50/CE on ambient air quality and cleaner air for Europe specifies the obligations of Member States regarding fixed measurements of atmospheric pollutants in areas where maximum concentration levels exceed the lower assessment threshold. However, indications as to the siting of atmospheric monitoring stations are less precise and sometimes confusing. Campaigns to measure benzene and other volatile organic compounds in Murcia in 2007 and 2008 revealed that the areas where measurements coincided with the mean concentration for the whole city were always practically the same. Consequently, we propose a method for siting atmospheric monitoring stations in cities for which emission sources remain steady throughout the year, as is the case for cities in most southern European countries, where the most important emission source is traffic. The method is particularly useful for towns in which only one fixed measuring point is compulsory and should help local authorities in making correct decisions in this context. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Fixed monitors constitute the way of accomplishing continuous monitoring of atmospheric pollutants. Directive 2008/50/EC (EC Directive, 2008) permits a maximum expanded uncertainty of 15e25% for such methods, depending on the pollutant in question, whereas indicative measurements and modelling techniques have wider margins of error of up to 25e50%. Several measurement methods can be used, alone or in combi- nation, depending on the concentrations of pollutants found in the air of a given zone. Directive 2008/50/EC defines upper and lower assessment thresholds and states that modelling or objective esti- mation techniques, which are less expensive than fixed measure- ments, can be used in areas where concentrations are below the lower threshold. If the concentrations are between the thresholds, monitoring can involve a combination of fixed and indicative measurements and/or modelling techniques, as long as the latter fulfil data quality objectives on maximum permitted uncertainty, in which case the minimum number of fixed measurements stipu- lated in the Annexe V.A of Directive 2008/50/EC can be reduced to half as a function of the population. In areas where the upper threshold is exceeded, evaluation must be carried out using at least the number of fixed measurements shown in mentioned Annexe. Pires et al. (2009) recently used principal component analysis to identify redundant measurements in air quality monitoring networks, focusing mainly on NO 2 ,O 3 and PM 10 in Oporto, Portugal. They concluded that the number of fixed measuring points for NO 2 and O 3 identified by the analysis coincides with that set out in the legislation, whereas two extra fixed measurement stations are needed for PM 10 for proper characterisation of the whole study area. Despite the lack of similar studies for other locations and pollutants, this finding suggests that the legislation in place does not over- estimate the minimum number of obligatory fixed sampling points needed. Although Directive 2008/50/EC is very specific about the number of sampling stations, it has no clear specification regarding the most suitable sites for such stations, stating that sampling points directed at the protection of human health shall be sited in such a way as to provide data on the following: (a) the areas within zones and agglomerations where the highest concentrations occur to which the population is likely to be directly or indirectly exposed for a period which is significant in relation to the averaging period of the limit value(s) and (b) levels in other areas within the zones and agglomerations which are representative of the exposure of the general population. A large number of European cities fall within the first band of population in Annexe V.A of Directive 2008/50/CE (0e249 000 inhabitants), so that they only require one measuring station for * Corresponding author. Tel.: þ34 868 887996; fax: þ34 868 884148. E-mail address: mdoval@um.es (M.D. Miñarro). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2010.03.044 Atmospheric Environment 44 (2010) 2640e2645