Impact of aging mechanism on model simulated carbonaceous aerosols
1Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, MI 49931, USA
2Atmospheric Science Program, Department of Geological and Mining Engineering and Sciences, Department of Civil and Environmental Engineering, Michigan Technological University, Houghton, MI 49931, USA
3Earth System Observations, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
4Michigan Tech Research Institute, Michigan Technological University, Ann Arbor, MI 48105, USA
Abstract. Carbonaceous aerosols that include organic carbon and black carbon, have significant implications for both climate and air quality. In the current global climate or chemical transport models, a simplified hydrophobic to hydrophilic conversion lifetime for carbonaceous aerosol (τ) is generally assumed, which is usually around 1 day. Based on results from recent chamber studies, we implemented a new detailed aging mechanism for carbonaceous aerosols in a chemical transport model (GEOS-Chem) where τ is affected by local conditions such as O3 concentration and humidity. The simulated τ exhibits large spatial and temporal variation with the global average calculated to be 4.3 days. The longest τ (up to 40 days for the Amazon forests) are found in the tropical areas, reflecting the low ozone concentration and high humidity there. The conversion lifetime generally decreases with altitude due to increases in ozone concentration and decreases in water vapor concentration. The updated aging mechanism has significant implications for model simulations of carbonaceous aerosols and improves the comparison to observations of carbonaceous aerosols. The strongest effects are found for the tropical regions and upper troposphere where the model simulated concentrations of black carbon and organic carbon increase by up to 0.16 μg C m−3 and 0.67 μg C m−3, respectively. This updated aging mechanism also leads to increases in model calculated global burden of black carbon and organic carbon by 31% and 17%, respectively. In addition, sensitivity studies show that the estimated continental outflow of carbonaceous aerosols would significantly increase with the updated aging mechanism.