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.

挥发性有机化合物（VOC）的排放来源很多，对植物适应性，生态相互作用和大气过程（包括光化学和臭氧形成）具有重要意义。森林生态系统是生物VOC的重要来源。我们的目标是在离巴塞罗那市区50公里的地中海森林蒙塞尼自然公园中，通过质子转移反应质谱法（PTR-MS）监测林下冠层VOC的混合比。在夏季最大排放期的六个月内，每2分钟进行一次测量。所有VOC都在白天具有较高的混合比率的diel循环，但随着时间的流逝会有不同的模式。监测的VOC分为生物源，氧化或芳族化合物。此外，一项积极的矩阵分解分析确定了四个排放特征，这些特征归因于光化学VOC的产生，生物源排放，混合VOC排放源和交通排放。即使该生物源是该地点最强的源剖面，我们也发现了人为的气团渗透到森林冠层并改变该地点的生物气团的强烈影响。