The aim of the study was to analyse relationship between PM2.5 and PM10 concentrations, traffic density and meteorological factors during the week with regular traffic regime and first week of COVID-19 lockdown in Novi Sad, Serbia. During the study period, which included working days and weekends, traffic emission contributions to PM were also determined. Obtained results have shown higher PM, pressure and emission contribution values, lower temperature, relative humidity values, and lower traffic counts for all vehicle categories during the COVID-19 week. A positive correlation was detected only during the first week, between PM2.5 and passenger vehicles and lightweight trucks, as well as between PM10 and all categories of vehicles. Background PM2.5 and PM10 concentrations were moderately correlated to total traffic during the first week as well. Very strong and moderate positive correlation was detected between PM2.5 and PM10 concentrations and temperature during COVID-19 week. The PM concentrations increased during COVID-19 week, but total traffic decreased by 31% on work-days and 42% on weekends, proving the impact of lockdown measures on traffic regime and intensity. Since relationship between PM2.5 and PM10 with different vehicle categories was confirmed only during first week, and PM and emission contribution concentrations were higher during COVID-19 week, a secondary emission source of PM was strongly indicated. Very strong and strong positive correlations of PM2.5 and PM10 with temperature during COVID-19 week have confirmed lower temperature impact on PM concentrations and, consequently, increased impact of heating, as an emission source, due to lockdown measures and people staying at their homes.