Evaluation of secondary organic aerosol (SOA) sources, growth, and sinks
Authors
Alma Hodzic — National Center for Atmospheric Research (NCAR)
Christoph Knote — Atmospheric Chemistry Division
Jose-Luis Jimenez — University of Colorado
Sasha Madronich — National Center for Atmospheric Research (NCAR)
Julia Lee-Taylor — National Center for Atmospheric Research (NCAR)
Sunil Baidar — University of Colorado, Boulder
Jerome D Fast — Pacific Northwest National Laboratory
Brett Palm — University of Colorado
Rainer Volkamer — University of Colorado
Category
Aerosol Properties
Description
The scientific understanding of processes involved in the formation, chemical ageing, and removal of secondary organic aerosol (SOA) is still very limited. Here we summarize the results of three regional and explicit-chemistry modeling studies of (1) SOA formation and regional growth over a pine forest in Colorado, (2) contribution of glyoxal to SOA formation in California (Carbonaceous Aerosols and Radiative Effects Study [CARES], California Nexus [CalNex]), (3) the effect of dry deposition of gases on SOA formation (Megacity Initiative: Local and Global Research Observations [MILAGRO], Mexico City).(1) The SOA formation and regional growth from biogenic precursors is of particular interest given their abundance in the atmosphere and has been investigated in 2011 in a pine forest using the Weather Research and Forecasting Chemistry (WRF-Chem) model and Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A). We have quantified the relative contribution of different biogenic precursors to SOA, and investigated the relative contribution of OH, O3 and NO3 chemistry to SOA mass and in situ SOA formation. We show that the optically active regional SOA is substantial due to the large area covered by forests as the SOA formation continues for several days in the background forest air. We investigate whether the simplified SOA parameterizations used in 3D models can capture this growth.
(2) The dominant fraction of SOA is thought to be formed via gas-phase oxidation of precursors, but recent laboratory and field studies suggest that aqueous and heterogeneous chemistry within the particle (e.g., from glyoxal) play an important role. In our study we investigate the regional contribution and variability of glyoxal to SOA formation using WRF-Chem that has been extended to include an updated description of the formation of glyoxal and its SOA. We find that Los Angeles is a hotspot for SOA from glyoxal and that a photochemically controlled pathway dominates. The improved model identifies a hot spot of glyoxal SOA in the southeastern US, and provides a useful tool for selection of locations for future studies.
(3) The dry deposition removal of organic compounds and its impact on SOA mass is currently poorly understood and represented in chemistry-climate models. The main reason for this omission is that current models use simplified SOA mechanisms, therefore losing information on other important properties of individual molecules that are needed to calculate dry deposition. Here, we apply GECKO-A to estimate the influence of dry deposition of gases on SOA concentrations downwind of Mexico City. We show that dry deposition of oxidized gases is not an efficient sink for SOA, as it removes <5% of SOA within the city's boundary layer and ~15% downwind.