Sensitivity of Carbonaceous Aerosol Properties to the Implementation of a Dynamic Aging Parameterization in the Regional Climate Model RegCM. Issue 17 (8th September 2021)

• Record Type: Journal Article
• Authors: Ghosh, Sudipta; Riemer, Nicole; Giuliani, Graziano; Giorgi, Filippo; Ganguly, Dilip; Dey, Sagnik
• Is Part Of: Journal of geophysical research. Volume 126:Issue 17(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-09-08
• Subjects: black carbon -- dynamic aging -- regional climate model -- India -- climate -- feedback; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2020JD033613
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: Freshly emitted soot is hydrophobic, but condensation of secondary aerosols and coagulation with other particles modify its hygroscopic optical properties. This conversion is referred to as "aerosol aging." Many climate models represent this aging process with a fixed aging time scale, whereas in reality, it is a dynamic process that depends on environmental conditions. Here, we implement a dynamic aging parameterization scheme in the regional climate model RegCM4 in place of the fixed aging timescale of 1.15 days (∼27.6 h) and examine its impact on the aerosol life cycle over the Indian subcontinent. The conversion from hydrophobic to hydrophilic aerosol is usually lower than 27.6 h over the entire landmass and lower than 10 h over the polluted Indo‐Gangetic Basin (IGB), with seasonal variability. Due to the implementation of the dynamic aging scheme, the column burden and surface mass concentration of carbonaceous aerosols increase during the drier season (December–February) when washout is negligible. The burden is reduced during the wet season (June–September) due to a more efficient washout except over the IGB, where a reduction in precipitation as a result of radiative feedbacks increases the aerosol concentrations. Over the polluted IGB, surface dimming increases due to the dynamic aging scheme, with the top of the atmosphere forcing remaining mostly unchanged. As a result, atmospheric heating increases by at least 1.2 W/m 2 . Our results suggest that climate models should incorporate dynamic aging for a more realistic representation of aerosol simulations, especially in highly polluted regions. Plain Language Summary: To understand the impacts of aerosols on air quality and climate, the models need to have a better representation of aerosol processes. One such example is the representation of soot, emitted from fossil‐fuel and biomass burning. Many climate models consider soot to be hydrophobic and keep its optical properties constant. However, in reality, this is not true. In this work, we implement the transformation of soot properties in the atmosphere in a regional climate model, RegCM. We found that the soot is converted to hygroscopic in only <10 h in the polluted regions of India relative to a fixed 27.6 h. We discuss the implication of incorporation of such transformation in terms of the changes in aerosol loading, mass concentration, and radiative forcing over the Indian Subcontinent. Key Points: Hydrophobic black carbon (BC) is converted to hydrophilic BC in <10 h in the polluted Indo‐Gangetic Plain as opposed to default 27.6 h in RegCM BC concentration increases in the dry season due to the dynamic aging, but reduces in the wet season due to an efficient washout Surface dimming increases due to the implementation of the dynamic aging scheme