Emissions variation in urban areas resulting from the introduction of natural gas vehicles: Application to Barcelona and Madrid Greater Areas (Spain) María Gonçalves a , Pedro Jiménez-Guerrero b , José M. Baldasano a,b, ⁎ a Environmental Modelling Laboratory, Technical University of Catalonia, Avda. Diagonal 647, Edificio H, Oficina 10.23, 08028 Barcelona, Spain b Barcelona Supercomputing Center – Centro Nacional de Supercomputación (BSC-CNS), Earth Sciences Department, Jordi Girona 29, Edificio Nexus II, 08034 Barcelona, Spain abstract article info Article history: Received 10 September 2008 Received in revised form 11 December 2008 Accepted 19 January 2009 Available online 5 March 2009 Keywords: Emissions Alternative fuels Urban pollution Natural gas vehicles Air quality management On-road traffic is the major contributor to pollutant emissions in urban areas. Nowadays different emission abatement strategies are being tested in order to improve urban air quality (e.g. the European Commission currently promotes the use of natural gas as an alternative fuel). Several feasible scenarios regarding the introduction of natural gas vehicles (NGV) are studied in the two main cities of Spain (Barcelona and Madrid) by using the HERMES emission model. The most suitable emission factors to NGV are selected among those available in the literature. The account of emissions in the base case scenario estimated for a typical summertime polluted day of the year 2004 reflects that in Barcelona 86% of primary pollutants come from on-road traffic compared to 93% in Madrid, because of the heavier industrial activity in the former. The introduction of NGV in urban zones would have a positive effect on emissions, whose extent largely depends on the substituted fleets and the conurbation characteristics. Maximum reductions in NO x emissions in Madrid are attributed to the substitution of 10% of the oldest diesel and petrol cars, while in Barcelona the change of 50% of the oldest commercial light vehicles becomes more effective. PM 2.5 and SO 2 emissions can be significatively reduced with the introduction of NGV instead of the oldest commercial light vehicles. The substitution of conventional fuels by natural gas must reach around 4% to achieve significative reductions in traffic emissions (larger than 5%). This work focuses on air quality issues, therefore GHG emissions are not included, nevertheless this kind of associated impact has to be considered by the decision makers. Assessing the efficacy of environmental improvement strategies entails a realistic design of emission scenarios and their evaluation. The detailed emission account provides a fundamental basis for the air quality modelling and its comparison among scenarios. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Atmospheric pollution is the environmental factor with the largest impact on human health in Europe and is responsible for the largest number of diseases related to the environment (EEA, 2005a). Tropospheric ozone and particulate matter affect the human health (EC, 2005; WHO, 2004). Specifically fine particles (diameter less than 2.5 μm) are associated with increased mortality (EEA, 2005b; Pope and Dockery, 2006). The largest contributions to the emissions of atmospheric pollutants in urban areas, where 80% dwellers in Europe live, come from the transportation sector, especially from on-road transport (Chin, 1996; Cirillo et al., 1996; Palmgren et al., 1996, 1999; Costa and Baldasano, 1996; Oduyemi and Dadvison, 1998; Colvile et al., 2001; Crabbe et al., 1999; Ghose et al., 2004). Technological improvements and emissions control legislation led to unitary emissions reduction by vehicle; nevertheless the increase of the vehicles number makes these efforts insufficient to accomplish the more and more restrictive air quality standards. Moreover in some cases the new technologies increase specific pollutant emissions; e.g. oxidation catalyst systems or particulate filters lead to an increase in NO 2 emissions (Carslaw et al., 2007). As well as a source of local pollution, urban activities contribute to transboundary pollution and the increase of greenhouse gases (GHG) concentration (Fenger, 1999; Baldasano et al., 2003). For all these reasons it is fundamental to evaluate the most suitable strategies for reducing the contribution of traffic emissions to air pollution in urban areas. Currently these strategies are mainly addressed to: (1) the reduction of km travelled (minimization of the number of vehicles and/or the distance travelled per vehicle); and (2) the reduction of unitary emissions by vehicle. The strategies to reduce the km travelled include public transport improvement, both from the infrastructural and service point of view; parking places restriction; roads construction to allow the easy flow of high occupation vehicles (taxis, buses or private cars with a high occupation rate); or the enhancement of mopeds and cycle roads. Also the introduction of taxes to use urban infrastructures contributes to a Science of the Total Environment 407 (2009) 3269–3281 ⁎ Corresponding author. Environmental Modelling Laboratory, Technical University of Catalonia, Avda. Diagonal 647, Edificio H, Oficina 10.23, 08028 Barcelona, Spain. Tel.: +34 934137719; fax: +34 934137721. E-mail address: jose.baldasano@bsc.es (J.M. Baldasano). 0048-9697/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2009.01.039 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv