AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Impact of Improved Representation of Aerosol Mixing State on Air-Quality-Weather Interactions
ROBIN STEVENS, Ashu Dastoor, Environment and Climate Change Canada
Abstract Number: 209 Working Group: Aerosols, Clouds and Climate
Abstract Aerosol chemical mixing-state, or the degree to which aerosol is internally- or externally-mixed, is important for both aerosol hygroscopic and radiative properties (Riemer et al. 2019; Stevens et al. 2019). Internal mixing of hydrophilic and hydrophobic species can allow the hydrophobic species to act as cloud condensation nuclei and to be more-efficiently removed by wet deposition. When internally-mixed, weakly-absorbing species act a lens on strongly-absorbing species (e.g. black carbon). This enhances absorption, compared to the case where the weakly- and strongly-absorbing species are externally-mixed. In the real atmosphere, aerosol is neither fully-externally-mixed nor fully-internally-mixed.
We implement a more-detailed representation of the aerosol mixing-state in the GEM-MACH air quality model with online air-quality-weather interactions. Our approach was inspired by MOSAIC-MIX (Ching et al. 2016): We independently account for both changes in hygroscopicity and black carbon mass fraction, as aerosol hygroscopic properties and radiative properties do not necessarily co-vary. The air-quality-weather interactions in GEM-MACH include aerosol-radiation interactions and changes in cloud droplet activation based on cloud condensation nuclei concentrations. We perform a case study focused on biomass-burning over North America to evaluate the results with the new representation of aerosol mixing state, both against the original size-resolved internally-mixed assumption and against observations. We investigate the interactions between the representation of aerosol mixing state and air-quality-weather interactions.
References: [1] Ching, J., et al. (2016). J. Geophys. Res. Atmos., doi:10.1002/2015JD024323. [2] Riemer, N., et al. (2019). Rev. Geophys., doi:10.1029/2018RG000615. [3] Stevens, R. and Dastoor, A. (2019). Atmosphere, doi:10.3390/atmos10040168.