EGU23-8498, updated on 22 Apr 2023
https://doi.org/10.5194/egusphere-egu23-8498
EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Representation of Precipitation Phases and a New Parameterization for Below-Cloud Scavenging in Regional Air Quality modelling

Roya Ghahreman, Wanmin Gong, Paul Makar, Alexandru Lupu, Amanda Cole, Kulbir Banwait, Colin Lee, and Ayodeji Akingunola
Roya Ghahreman et al.
  • Environment and Climate Change Canada, North York, Canada (roya.ghahreman@canada.ca)

Below-cloud scavenging is the process of aerosol removal from the atmosphere between cloud-base and the ground by precipitation (e.g. rain or snow), and affects aerosol number/mass concentrations, lifetime and distributions. An accurate representation of precipitation phases is important in treating below-cloud scavenging as the efficiency of aerosol scavenging differs significantly between liquid and solid precipitation. To study cloud processes and precipitation chemistry, we examined representation of below-cloud aerosol scavenging of in the current GEM-MACH model, including a revised approach in precipitation phase partitioning and implementing a new aerosol below-cloud scavenging scheme (from Wang et al., 2014) and comparing with the GEM-MACH’s existing scavenging scheme, based on Slinn (1984). 

Overall, the multi-phase partitioning and Wang et al. (2014) scavenging scheme improve GEM-MACH performance as compared with observations. Including multi-phase approach leads to a decrease on SO42- scavenging and impacts the below-cloud scavenging of SO2 into the aqueous phase. The impact of the new scheme on wet deposition of NO3- and NH4+ varies, with both increases and decreases in wet scavenging, and is more important at specific cloud locations. The two aerosol scavenging rates differ during liquid precipitation in the 0.1-1 µm size range mostly at high precipitation intensity. The two aerosol scavenging schemes diverge for aerosols smaller than 1 µm for solid precipitation at lower intensity (R=0.01 mm/h), while at higher precipitation intensities (R=10 mm/h), the two schemes show larger differences for aerosols larger than 1 µm. The changes on the speciated particles (sulphate, nitrate and ammonium) are consistent with the changes in the wet scavenging, leading to higher modelled concentrations of particulate sulphate in the atmosphere.

How to cite: Ghahreman, R., Gong, W., Makar, P., Lupu, A., Cole, A., Banwait, K., Lee, C., and Akingunola, A.: Representation of Precipitation Phases and a New Parameterization for Below-Cloud Scavenging in Regional Air Quality modelling, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8498, https://doi.org/10.5194/egusphere-egu23-8498, 2023.