Long term observations of PM2.5 and precursor gases using high temporal resolution measurements provide valuable information to understand the nature and variability of sources, secondary aerosol formation processes, fate and evolution of these complex pollutants. For the first time in the densely-populated region of the North of France, regularly exposed to high PM episodes, a 1-year campaign was conducted in a rural village (433 inh.), 90 km NE of Paris, in 2018. VOCs, inorganic precursor gases and PM2.5 speciation were measured hourly, along with local weather parameters (Table 1). Methods Chemical composition, ionic balance, mass closure of the PM2.5 and statistical analysis were performed to validate the database and determine the levels and main correlations of the measured species. Time variability profiles at hourly, weekly, seasonal and annual scales were compared to a comparable 1-year long campaign done in 2015-2016 at a suburban site of Douai (40,736 inh) in the same region by Roig et al. (2019). A seasonal source apportionment analysis was performed by Positive Matrix Factorization (PMF), in order to detect source contributions to the regional loading of PM2.5. The geographical origin of the pollutants and source factors was determined by Non-parametric Wind Regression and 72h backward air mass trajectories analysis using Concentration Field (CF) and Potential Source Contribution Function (PSCF) methods. Main findings While PM2.5 concentrations are slightly lower at the rural site than at the suburban one (Figure 1), their chemical composition is similarly dominated by Secondary Inorganic Aerosols (SIA, mainly NH4NO3 and (NH4)2SO4) accounting for more than 50 %, regardless of the season, in accordance with other studies (Putaud et al,. 2010). However, the relative distribution of particulate sulfate and nitrate vary. The hourly variability of SIA is similar at both sites, despite of differences for precursor gases (e.g. SO2 and HONO) suggesting changes in the strength of local sources (industries and traffic), and possible additional sources related to soil HONO (Su et al., 2011). Differences on the levels of NH3 and NOx between sites point out to different chemical regimes, locally governing the atmospheric chemistry. These results confirm a strong regional background of SIA from distant sources. The highest PM2.5 concentrations are due to transboundary processes occurring mostly during winter and spring as highlighted in CF and PSCF maps (Figure 2). This study confirms the usefulness of long-term high-resolution observations from different site typologies