Abstract
The paper highlights the contribution of the road traffic to PM2.5 air pollution, taking in consideration the atmospheric parameters. But, despite other studies, temperature and relative humidity are considered as moderating variable. The concentration of particulate matter is also influenced by local geography, urban structure, and streets shape. The case study was done in Bucharest, in an open area. The PM2.5 air concentration time series is proved stationary, an autoregressive model with two lags being tested. While the main effects of road traffic and humidity are significant, temperature has not a significant direct effect. But both moderators show interactive effects. The conditional effects are getting down with increase in temperature and humidity, due to changes in air dynamics and precipitation phenomena.