modeling of co and nox produced by vehicles in mashhad, 2012

background: in large cities, the share of vehicles in air pollutants emissions is nearly 70% that is mainly due to use of fossil fuels. environmental simulation has many advantages such as accuracy and speed of modeling. present study was conducted to create a model of air pollution [carbon monoxide (co) and nitrogen oxides (nox)] from vehicles in fifty following years, in mashhad. methods: according to the collected data from license plate, traffic and transportation organizations, modeling of co and nox was performed by stella software. hence, five strategies, including reduction in the number of imported vehicles and the proportion of distance traveled by vehicles, increase in the number of junked vehicles, application of euro 4 standards instead of euro 3 and a combination of their application, were applied in the model. results: in the current condition, co and nox concentrations are 27,894 and 2,121, and after 50 years they would be 26,227,930 and 2,070,011 ton/year, respectively. applying the aforementioned strategies, their concentrations were declined approximately (35% and 35%), (50% and 50%), (16% and 16%), (7% and 47%) and (75% and 85%), correspondingly. conclusion: developed model showed that if the present condition remains stable, air quality will be more and more undesirable in the 50 following years. however, application of the second method, reduction of the distance traveled, was the most effective strategy in reducing the amounts of ones, so it will be better that this strategy is considered in the administrative policies. nevertheless, as far as possible all of them ought to be taken advantage of.