Ozone as secondary air pollutant is formed from nitrogen oxides and hydrocarbons in the presence of UV radiation (sun). Both polluting agents, NO₂ and O₃, are connected with typical concentration relation (see Figure 7). In the central part of the city high ozone concentrations are observed in the afternoon and early morning hours. Higher ozone concentrations in Riga are measured during Spring and Summer (see Figure 8).

Highest ozone concentrations in Riga are measured by background stations at Kengarags and Imanta regions (data of State Hydrometeorological Agency).