Winter to spring transition and diurnal variation of VOCs in Finland at an urban background site and a rural site

We measured volatile organic compound (VOC) volume mixing ratios (VMRs) using a quadrupole proton-transfer-reaction mass spectrometer, and investigated the differences between winter and spring VMRs and sources at an urban background site in Helsinki (2006) and a rural site in Hyytiala (2007) utilizing a receptor model EPA Unmix. In Helsinki, VMRs of VOCs were typically higher,and their diurnal variations were more pronounced than at the rural site. At both sites, monoterpenes have anthropogenic influence in winter, while in spring biogenic influence is dominating. At the urban background site, the main aromatic hydrocarbon source was traffic, which also explained most of the oxidated VOCs during the urban winter. At other times and at the rural location most of oxidated VOCs originated mainly from distant sources. At the rural site, traffic and distant sources contributed equally to the aromatics in winter but in spring the distant source dominated.