Sesquiterpene emissions from loblolly pine and their potential contribution to biogenic aerosol formation in the Southeastern US

Sesquiterpene (SQT) and montoterpene (MT) emissions from loblolly pine (Pinus taeda L.) were studied by branch enclosure experiments at Duke Forest in Chapel Hill, NC. Four SQT (β-caryophyllene, α-bergamotene, α-humulene, β-farnesene), five MT (α-pinene, β-pinene, β-myrcene, β-phellandrene, limonene), and the oxygenated MT linalool were identified. Emission rates of both compound classes increased exponentially with temperature, albeit SQT temperature coefficients (0.12–0.18 K−1) were higher than for MT (0.068–0.15 K−1), resulting in an increased contribution of SQT to the overall biogenic volatile organic compound (BVOC) flux during warm temperature conditions. The highly correlated variables of light and temperature conditions preclude a rigorous characterization of their individual roles in driving these emissions. However, the observations indicate that there may be both temperature-only and temperature/light-dependent components contributing to SQT emission variations. When normalized to 30 °C using the best-fit temperature algorithm, total SQT basal emission rate was 450 ng g−1 h−1. The potential contribution of SQT from all pine trees (based on the loblolly pine emission factors) to secondary, biogenic organic aerosol in 12 southeastern US states was estimated to be 7×106 kg for the month of September which constitutes an appreciable portion of the overall PM 2.5 emission budget.