Another notable finding is the pollutant that dominates the AQI value at each site. During the winter, in the street canyon, the dominant pollutant is the NOx, in the urban square the PM10 and in the urban park the O3. During the summer, under typical summer climatic conditions, at all sites the dominant pollutant is the PM10, but in high solar radiation conditions the O3 becomes the dominant pollutant. Elevated O3 levels result by photochemical reaction of volatile organic compounds (VOCs) like isoprene and monomers panes, which can contribute to the formation of secondary such as (O3), under high solar radiation and temperature values (Donovan et al., 2005)