Granted that causing welfare increases in urban areas, industrial Revolution has started to exhaust and destroy the environment terribly. Consequently, importance of the environmental protection was started to be recognized as one of the principle concerns of the latter half of the 20th century, and has dominated political agenda at the beginning of third millennium. However there is an increasing recognition of the need to protect environment, losses and degradations have continued in all over the world. One reason is that economic values of environment do not take part in the economic decision processes; as a result, a number of methods were improved to value environmental goods to integrate inside the economic decision process in the developing world. Contingent Valuation approach (CVA) is one of those approaches that are used to integrate the benefits of public goods and services such as forests, water, air etc. into economical decision process By using cross-section data of Mashhad which were gathered through a survey research in 2005-2006, and applying contingent valuation approach and Heckit model this study has tried to determine economical value of air pollution 30 Percent improvement and effective factors on people WTP. Results showed that 30 percent improvement of air pollution quality total value in high-polluted region equals 7134146560 Rials per month and in middle-polluted region equals 5242428950 Rials per month. Therefore according to citizens’ mentality, value of 30 percent improvement of Mashhad air pollution state equals 12376575510 Rials per month. Based on results of this study, in decision-making stage, education level, age, kind of settlement region, sex and having child are significant variables on citizens\\\' WTP for air pollution reduction. In addition education level, sex, age, household income, having child and having car are effective factors on people willingness to pay in administrating stage.

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