Examining some potential actions in mitigating gaseous emissions from vehicles, case study: Tehran Madjid Delkash 1 & Hussein M. Mir 2 Received: 10 January 2016 /Accepted: 21 March 2016 # Springer Science+Business Media Dordrecht 2016 Abstract Pollutant emission from vehicles is known as a ma- jor air pollution source in metropolitan areas. Efficiency of several solutions was quantified and compared to introduce the best solution for decreasing greenhouse gases and air pol- lutant emissions: (1) inspection and maintenance (I/M) of ve- hicles, (2) restriction of air conditioner usage, (3) injecting better quality fuel (removing sulfur), and (4) replacing older vehicles with new ones were modeled by International Vehicle Emissions (IVE) model as potential solutions. Restricting air conditioner usage makes an insignificant contribution in pol- lutants’ emission. The idle inspection/ maintenance system can reduce carbon monoxide (CO) and methane (CH 4 ) emis- sion by about 10.7 and 3.8 %, respectively. The loaded I/M system reduces nitrogen oxides (NO x ), CO, volatile organic carbon (VOC), and CH 4 emission by 8.6, 11.5, 3.4, and 7.6 %, respectively. Effect of I/M programs depends on the types of vehicles and target pollutants needed to be reduced. Sulfur emission into the atmosphere would be reduced remarkably (about 98 %) if its concentration was reduced in fuels. Substitution of old vehicles with new vehicles makes a notice- able contribution in improving air quality (about 53 % reduc- tions in CO, 52 % in VOC, and 58 % in CH 4 emission for light-duty vehicles). Analytical hierarchy process (AHP) was utilized to identify the most feasible solution for reducing air pollution. Fuel quality improvement and replacing old cars with newer ones are the most tangible solutions, respectively. This paper demonstrates that each policy has its own impact on emission and we can apply each of them in cases in which the pollutants concentrations are high. Keywords Air Pollution . Greenhouse gas . Decision making . International Vehicle Emission Model . Urban policies Introduction The increasing number of vehicles all around the world is ex- acerbating the ambient air quality (Guttikunda et al. 2015; Fujita et al. 2015; Hassanvand et al. 2015). Understanding the types and concentrations of hazardous pollutants emitted into the atmosphere is vital for public health considerations (Baldauf et al. 2009; Youssefi and Waring 2015). Evidence demonstrates that there is a close relationship between exposure to air pollu- tion and some diseases such as stroke, heart disease, and myo- cardial infarction (Grahame and Schlesinger 2010; Ayala et al. 2012; Youssefi and Waring 2012, 2014). The United Nations reported that more than 600 million people encounter danger- ous air pollution caused by traffic (Cacciola et al. 2002). The Iranian health ministry stated air pollution kills over 3500 peo- ple in Tehran annually (Samaras 1999). Scientists and gover- nors have paid significant attention to the vehicles’ pollutant impact on climate change and environmental degradation as a global issue (Ndetto and Matzarakis 2015). Different approaches have been employed to estimate pol- lutant emissions from mobile sources in megacities. Using other countries’ emission factors to estimate emissions from a certain region is the simplest approach that might have high uncertainties. This approach is popular for countries without essential data to localize emission estimation models. The US * Madjid Delkash delkash@udel.edu 1 Department of Civil and Environmental Engineering, University of Delaware, Newark, DE, USA 2 Department of Civil Engineering, Sharif University of Technology, Tehran, Iran Air Qual Atmos Health DOI 10.1007/s11869-016-0400-9