10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Quantifying Errors in CCN Concentration and Aerosol Optical Properties Caused by a Non-Interactive Coarse Mode Using a Particle-Resolved Aerosol Model
JESSICA GASPARIK, Nicole Riemer, Jeffrey H. Curtis, University of Illinois at Urbana-Champaign
Abstract Number: 932 Working Group: Aerosol Modeling
Abstract Coarse mode aerosols are generally considered to be particles of primary origins (e.g., dust, sea salt, pollen, small pieces of rubber from automobile tires) with diameters greater than ~2 μm. They are emitted into the atmosphere through mechanical processes and have a lifetime on the order of hours to days. Although this is a relatively short lifetime, many coarse mode particles still have sufficient opportunities to interact with finer mode aerosol particles (including Aitken, and accumulation modes) by coagulation, or provide surface area where secondary aerosol material can condense on, causing changes in the distribution of aerosol number mass. However, in many global models the coarse mode is treated as non-interactive, meaning they do not consider coagulation of coarse mode particles with the rest of the distribution and interaction with the gas phase. While this reduces computational cost, it may introduce significant error in predictions of the size distribution, cloud condensation nuclei (CCN) concentrations, and aerosol optical properties. The objective of this study is to assess the interactions between the coarse mode with other particle size ranges and determine the conditions where it is acceptable to treat the coarse mode as non-interactive.
For this study, we used a particle resolved model, PartMC-MOSAIC coupled with the WRF model. The model resolves the aerosol composition on a per-particle level in a Eulerian single-column domain and couples the aerosol and gas-phase chemistry with the meteorology. We constructed a suite of scenarios representative of a large urban area and simulated the evolution of aerosols of different emission types due to coagulation, condensation of secondary aerosol, and vertical mixing within the column. We varied the emissions of coarse mode and finer modes, particularly from combustion sources along with the vertical mixing by turbulent diffusion within the column. In each scenario, we compared the aerosol properties when the coarse mode is treated as interactive versus non-interactive, with respect to time and height. Based on this error, we identified conditions when it is acceptable to consider the coarse mode as non-interactive.