VOLATILE ORGANIC COMPOUND EMISSIONS AND SECONDARY ORGANIC AEROSOLS FORMATION DURING CLEARCUTTING OF A BOREAL FOREST AT NORUNDA, SWEDEN

Abstract

Emissions of biogenic volatile organic compounds (BVOCs) from boreal forest are a significant source to the global carbon emissions budget. Clearcutting, which is the most used method during forest harvesting in Sweden, can potentially lead to increased emissions of BVOC and subsequently SOA formation. In this study, we conducted observations of BVOCs oxidation products before and during an active clearcut at Norunda, Sweden, using a Filter Inlet for Gases and Aerosols (FIGAERO) coupled to a Chemical Ionization Mass Spectrometer (CIMS). We compared the oxidation products in both gas- and particle phases to their precursor VOCs. We found that during clearcutting, monoterpenes and sesquiterpenes had high temporary spikes and the averaged concentration increased by a factor of 2.8 and 3.0 respectively, while isoprene did not have spikes and averaged concentration decreased by half. The high temporary spikes in total VOCs concentration during the clearcut may have caused changes in how precursor VOCs are oxidised and that diurnal patterns changed during the clearcut. The oxidised compounds were further grouped into monoterpene-, isoprene- and sesquiterpene oxidation products based on the number of carbon atoms that they contained. All three groups showed an increased ratio during the clearcut, in both gas and particle phases, indicating an overall enhancement of their contribution to particle formation. Finally, implications that clearcutting can have on climate were discussed.