Background and purpose: Because of the high traffic flow in the city center in Sari, a walk through survey indicated that the PM2.5 concentrations are likely to be higher than the standards. This study was carried out to determine the level of PM2.5 at the streets' curbsides in the city center in Sari.

Materials and Methods: In this cross-sectional study the PM2.5 concentrations were measured in 185 monitoring stations at the curbsides of four main streets in the Sari city  entre. 5550 10-s samples were collected using a real time particle monitor. A questionnaire was used to record air pollution related information and data were analyzed by descriptive statistic and ANOVA tests.

Results: Mean of PM2.5 concentration was 83μgm-3 and it was two times more than the national one and EPA recommended 24- hour standard (35μgm-3). This study showed that mean of PM2.5 concentration at the street during traffic rush hours in the morning and evening were higher than those measured in the afternoon.

Conclusion: Because of the high concentration of PM2.5 in the Sari’s city centre that resulted in this study, the 24- hour PM2.5 concentrations are likely to be higher than standards in some days in the city centre in Sari. Therefore, monitoring and control of air pollution are recommended in this city.