AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Chemical Mechanisms Behind the Isoprene Suppression of Biogenic New Particle Formation
SHANHU LEE, Yi You, Janek Uin, Alex Guenther, Joost de Gouw, William Brune, Paul Wennberg, Alex Teng, Tran Nguyen, Jason St. Clair, John Crounse, Pawel Misztal, Gabriel Isaacman, Allen H. Goldstein, Karsten Baumann, Eric Edgerton, Kent State University
Abstract Number: 351 Working Group: Advances in the Physics and Chemistry of New Particle Formation and Growth
Abstract Secondary aerosol formation in forests is a significant source of atmospheric aerosol particles. We have investigated the process of new particle formation in a mixed deciduous forest under anthropogenic influences, during the Southern Oxidant and Aerosol Study (SOAS) in the summer of 2013 in the state of Alabama. Particle size distributions down to approximately 1 nm and concentrations of various gas-phase nucleation precursors such as sulfuric acid, ammonia/amines, isoprene, monoterpenes, and various oxidation products of biogenic VOCs were measured. There was a complete absence of new particle formation during the six weeks of the campaign in June and July. Frequent sub-2 nm cluster formation with peak concentrations in the 10000 particles per cubic centimeter range occurred and they were strongly correlated to sulfuric acid/sulfur dioxide concentrations. However, no subsequent growth of these clusters to larger sizes was observed. Additionally, the measured sub-2 nm cluster concentrations showed a strong difference between day and night (2 to 3 orders of magnitude lower at night), in contrast to the previous reports from the Finnish boreal forest which showed a constant particle pool in the sub-2 nm size range. Several factors, such as high temperatures and high condensation sink can partially explain the lack of the cluster growth, but the conditions should have been favorable for new particle formation on some of the campaign days. Previous chamber experiments, field observations and the comparison of relevant atmospheric conditions from this and other measurement sites (a Michigan deciduous forest and Amazon rain forests), consistently point to high isoprene emissions as the likely reason for the lack of new particle formation in the mixed forest. From these observations, we propose several chemical mechanisms behind the isoprene suppression of biogenic new particle formation.