Assessing volatile organic compound sources in a boreal forest using positive matrix factorization (PMF)

Ambient volatile organic compound (VOC) concentrations including individual monoterpenoids, sesquiterpenes (SQTs), isoprene, 2-methyl-3-buten-1-ol (MBO), methacrolein (MACR), C5-C10 aldehydes, benzene and toluene were measured in a coniferous forest in Hyytia center dot la center dot, southern Finland, in April-November 2016 with 1-2 h time resolution. Positive matrix factorization (PMF) was used to resolve the major sources which were responsible for the observed ambient VOC concentrations. The most reliable results were obtained with a 10 factor solution including four anthropogenic and six biogenic sources. Three of the biogenic factors were induced by light. They were either light dependent emissions or products of photochemical reactions. Three factors appeared to be temperature dependent emissions. Biogenic emissions were clearly the most important source of the measured VOCs, but the contribution from a local sawmill was also significant. About half of the monoterpenes (MTs) could be appointed to Scots pine emissions, but the influence from the activities at a near-by sawmill and Norway spruce emissions were also found. In the case of some individual MTs (e.g. limonene), spruce emissions dominated. Spruce emissions were also mainly responsible for ambient SQTs, aldehydes, and isoprene. For anthropogenic compounds, benzene and toluene, background, and local activities were the main sources. PMF was useful in resolving the sources of ambient VOCs.