New particle formation at a peri-urban agricultural site br

New Particle Formation (NPF) is a major source of ultrafine particles that affect both air quality and climate. Despiteemissions from agricultural activities having a strong potential to lead to NPF, little is known about NPF within agri-cultural environments. The aim of the present study was to investigate the occurrence of NPF events at an agriculturalsite, and any potential relationship between agricultural emissions and NPF events. Afield campaign was conductedfor 3 months at the FR-Gri-ICOS site (France), at an experimental farm 25 km west of Paris city centre.16 NPF events have been identified from the analysis of particle number size distributions; 8 during the daytime, and 8during the night-time. High solar radiation and ozone mixing ratios were observed during the days NPF occurred, sug-gesting photochemistry plays a key role in daytime NPF. These events were also associated with higher levels of VOCssuch as isoprene, methanol, or toluene compared to non-event days. However, ammonia levels were lower during day-time NPF events, contributing to the hypothesis that daytime NPF events were not related to agricultural activities.On the other hand, temperature and ozone were lower during the nights when NPF events were observed, whereasrelative humidity was higher. During these nights, higher concentrations of NO2and ammonia were observed. As aresult, agricultural activities, in particular the spreading of fertiliser on surrounding crops, are suspected to contributeto night-time NPF events.Finally, all the identified NPF events were also observed at SIRTA monitoring station 20 km from the FR-Gri ICOS site,showing that both night-time and daytime NPF events were regional processes. We hypothesise that night-time NPFmay be related to fertiliser spreading over a regional scale, as opposed to the local activities at the farm. To our knowl-edge, this is thefirst time night-time NPF has been observed in the agricultural context