Dynamics of volatile organic compounds in a western Mediterranean oak forest

Volatile organic compounds (VOCs) are emitted from many sources and have important implications for plant fitness, ecological interactions, and atmospheric processes, including photochemistry and ozone formation. Forest ecosystems are strong sources of biogenic VOCs. We aimed to characterize forest below-canopy VOC mixing ratios, monitored by Proton Transfer Reaction Mass Spectrometry (PTR-MS), at Montseny Natural Park, a Mediterranean forest 50 km from the Barcelona urban area. Measurements were taken every 2 min during six months around the maximum emission period of summer. All VOCs had diel cycles with higher mixing ratios during the day, but different patterns over time. Monitored VOCs were grouped as biogenic, oxygenated, or aromatic compounds. Additionally, a positive matrix factorization analysis identified four emission profiles that were attributed to photochemical VOC production, biogenic emissions, mixed VOC emission sources, and traffic emissions. Even though the biogenic source was the strongest source profile at the site, we found a strong influence of anthropogenic air masses infiltrating the forest canopy and altering the biogenic air masses at the site.AMYS, JP, IF, and JL acknowledge funding provided by the Spanish Government grant PID2019-110521GB-I00, the European Research Council Synergy grant ERC-SyG-2013-610028 IMBALANCE-P, and the Catalan Government grant SGR 2017-1005. AMYS also acknowledges the Spanish Ministry of Education and Science for her Juan de la Cierva-Incorporación grant. We would like to especially thank Joana Barber and Daniel Guinart from the Biosphere Reserve of Montseny Natural Park for allowing us to use the park facilities for the study.Peer reviewe