Suppression of New Particle Formation by Isoprene in Non-Pristine Mixed Forest Environments

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With support from the Environmental Chemical Sciences Program in the Division of Chemistry at NSF, Shanhu Lee and Bernhard Vogler at the University of Alabama in Huntsville (UAH) and their graduate students will conduct laboratory kinetics studies to investigate chemical mechanisms related to the suppression of new particle formation (NPF) by isoprene, a very important biogenic hydrocarbon, in the atmosphere in forested areas. NPF contributes significantly to global cloud condensation nuclei production, impacting clouds and climate. Recent laboratory studies have demonstrated that isoprene suppresses biogenic new particle formation, but these studies were mostly limited to the conditions that mimic pristine forest conditions. This study focuses on conditions that are closely relevant to the mixed deciduous forests in the United States and include both biogenic terpenes and various pollutants. The scientific findings will be incorporated into outreach programs at UAH to communicate climate and environmental issues to multiple age groups ranging from K-12 to the general public.This project will employ a dual-flow tube system known as the TANGENT (Tandem Aerosol Nucleation and Growth ENvironment Tubes) system developed by the Lee and Vogler team to conduct multi-component nucleation and growth involving terpene-produced HOMs (highly oxygenated organic molecules), sulfuric acid, ammonia, amines, and NOx. The TANGENT system will allow the team to study nucleation and the subsequent growth of new particles independently under controlled experimental conditions. Gas-phase nucleation precursors, aerosol size, and particle-phase chemical composition will be measured with a series of state-of-the art chemical and aerosol instruments. These studies are will represent one of the most comprehensive laboratory observations yet made to study the role of isoprene on nucleation vs. growth of new particles under conditions representative of non-pristine mixed deciduous forests and at a wide range of temperature and relative humidity conditions. This fundamental research is expected to provide new insight into the role of this important biogenic volatile organic compound-isoprene-upon particle formation relevant to cloud condensation and hence climate conditions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.