LAUSR

Abstract Measurements of inorganic precursor gases (NO, NO2, HONO, NH3, SO2 and HCl) and PM2.5 inorganic water-soluble ions (NO3−, SO42−, NH4+, Cl−, Na+, Mg2+, Ca2+, K+) were performed at a suburban site in northern France for the first time using a MARGA 1S with an hourly time-resolution from August 2015 to July 2016. The observations were compared with other independent methods: HR-ToF-AMS, BAM-1020, SO2 and NH3 gas monitors over shorter time periods. The dominant particulate species were NO3−, SO42− and NH4+, with average annual mass contributions to PM2.5 of 28.0%, 13.1% and 9.9%, respectively. The highest concentrations of SIA were found in spring likely due to increased agricultural emissions of precursor gases. A strong formation of ammonium nitrate (NH4NO3) over nighttime was observed for every season and attributed to the condensation of its gaseous precursors NH3 and HNO3. The partitioning of NH4NO3 between the gas and particulate phases was compared with that obtained with the thermodynamic module ISORROPIA II and generally found to agree well except for HNO3. The local or distant origin of each species was determined by means of Non parametric Wind Regression (NWR) polar plots and Potential Source Contribution Function (PSCF) maps. SIA main origins were regional with significant contributions from Belgium, the Netherlands and western Germany. Additionally, several high PM2.5 episodes that lasted more than 2 days were analyzed, showing some common features.