Introduction and purpose: Carbon monoxide (CO) and particulate matter (PM 2.5) are among the most important environmental pollutants arising from different sources, such as vehicle exhaust, industrial process, and secondary pollutants. These pollutants lead to increased pulmonary vascular diseases and decreased vision. Moreover, they damage the plants, animals, and objects. The aim of this study was to investigate the concentration trend of these pollutants in Mashhad, Iran, during 2016.

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... : In this study, the data of the Air Quality Control Company were used to assess the concentration of CO and PM 2.5. In addition, the meteorological data, such as wind velocity and temperature, were extracted. Results: According to the monthly average CO concentration, CO had the highest and lowest concentration levels in December and May, respectively. Furthermore, regarding PM 2.5 , the maximum and minimum concentration values were observed in May and January, respectively. In 58.3% of the cases, the PM 2.5 concentration was higher than the standard values. The results of the statistical test revealed that the concentration of CO and PM 2.5 had a significant relationship with temperature and relative humidity. However, no significant relationship was observed between wind velocity and concentration of the pollutants. Conclusion: The results of the study showed that the summer and fall had the highest level of pollution. Furthermore, the pollutant concentration was higher than the standard values in most of the cases. Given that high concentration of pollutants affects the public health, the awareness of air quality at different periods and variations of air pollutant concentration can have an important role in urban health management.