Different heating systems in Riga (urban central heating system managed by municipal enterprise "Rigas Siltums", different medium power local boilers, which belongs to different institutions, as well as boilers in private houses) are responsible for SO₂ pollution in the city.

Presently, sulphur dioxide concentrations are mostly connected with the heating season, therefore highest pollution is in the Winter (see Figure 4).

Inventory of SO₂ emissions includes only larger sources (with heating power more than 0.2 MW), therefore modelling of SO₂ dispersion from stationary sources and comparison with the measured background values allows us to estimate the share in SO₂ concentrations from private houses, medium power boiler houses, as well as ships and tankers moving in Daugava River in the Passenger and Industrial ports.