AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Nucleation and Growth Under High Oh Conditions: Using an Oxidation Flow Reactor and the Tomas Box Model to Learn About Chemistry, Nucleation, and Growth Potential of Ambient Pine-Forest Air
ANNA HODSHIRE, Brett Palm, Jose-Luis Jimenez, Qijing Bian, Jeffrey R. Pierce, Pedro Campuzano-Jost, Douglas Day, Zhe Peng, Amber Ortega, James Hunter, Eben Cross, Jesse Kroll, Lisa Kaser, Werner Jud, Thomas Karl, Armin Hansel, Colorado State University
Abstract Number: 59 Working Group: Regional and Global Air Quality and Climate Modeling
Abstract Volatile organic compounds (VOCs) and semivolatile and intermediate-volatility organic compounds (S/IVOCs) can undergo oxidative aging to form lower-volatility compounds that can then participate in secondary organic aerosol (SOA) formation. Recent studies have shown that a portion of SOA species are major contributors to nucleation and growth in many regions of the atmosphere. The majority of studies on SOA formation have focused on determining the SOA potential of single SOA-precursor VOC (e.g. α-pinene) rather than ambient mixtures of VOCs and S/IVOCs; furthermore, many of these studies have used “smog” chambers, which are highly susceptible to losses of both particles and vapors to the walls. The oxidation flow reactor (OFR) was developed in order to both study the SOA potential of ambient air and minimize wall losses by using a short residence time. OFRs can simulate high and variable oxidant concentrations, with the aim of simulating days to weeks of atmospheric aging in ~2-4 minutes. OFR studies to date have focused on aerosol mass and aging. In this presentation, we discuss the nucleation, growth, and size-distribution dynamics from an OFR deployed at the 2011 BEACHON-RoMBAS campaign in a ponderosa pine forest of Colorado, USA. This is, to our knowledge, the first time particle size distributions have been examined from an OFR study. We show that in order to model the evolving distributions, gas-phase fragmentation of the lowest-volatility species, heterogeneous chemistry, and diffusion limitations at larger particle sizes must be considered along with nucleation, condensation, and coagulation. We explore the parameter spaces of the rate constants of nucleation, OH oxidation, gas-phase fragmentation, heterogeneous chemistry, and diffusion limitations in order to determine what set(s) of parameters are best able to simulate the OFR size distributions.