Concentrations of air pollutants mainly depend on meteorological conditions and pollutant emission levels. Airborne particulate matter (PM2.5 and PM10) concentrations were measured in Riga (Latvia) from the end of April to the end of December 2007. The collected particulate matter was analyzed for the anion, cation and heavy metal content. The seasonal variations of particulate matter concentrations were investigated, together with their relationships with meteorological parameters and other pollutant gases. The maximum daily concentration of PM2.5 and PM10 reached 52.5 g/m3 in June and 83.4 g/m3 in December, respectively.