Identifying and Zoning the Nitrogen Dioxide Hotspots in Mashhad

Nitrogen dioxide is one of the standard pollutants that in addition to adverse health effects, is also a prerequisite for the formation of hazardous atmospheric compounds. Based on 84 monthly maps, which are drawn from the maximum number of air quality stations and the longest possible statistical period, four seasonal maps of NO2 distribution were prepared for Mashhad city. Then, using Getis–Ord-Gi index, the hot spots of this pollutant were identified on seasonal maps. Using hierarchical cluster analysis, homogeneous NO2 areas of Mashhad were identified. According to the results, the spatial pattern of the formation of hotspots is similar in all seasons and covers most of the eastern and northeastern regions of Mashhad. Moreover, in terms of the concentration of pollutants, Mashhad can be divided into three homogeneous zones or areas. Region 1 with moderate concentration covers 24% of the city area in the southern and southwestern of the city. Zone 2 with the lowest concentration that covers 50% of the city area corresponds to the western half of Mashhad and is located in this zone, and finally Zone 3 with high concentration, mainly includes the eastern and northeastern parts of Mashhad.High population density compared to other regions, lack of infrastructure, urban transport network, old motor vehicles and proximity to the suburbs of production and industrial units may be reasons for high concentration of NO2 formation in this region. The results of this study can be used as a source of specialized information for developing programs for monitoring, reducing and controling NO2 pollutants in Mashhad.