Investigating the impacts of entrainment on nucleation scavenging of black carbon particles through particle-resolved simulations

black carbon;entrainment;cloud physics;PartMC-MOSAIC

Jones, Amanda ; Riemer ; Nicole

关键词: black carbon;    entrainment;    cloud physics;    PartMC-MOSAIC;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/49492/Amanda_Jones.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Aerosol particles have the ability to alter our climate by direct and indirect effects. Black carbon is a unique aerosol in that along with scattering, it can also absorb solar radiation, which heats the atmosphere and contributes to a positive radiative forcing. The optical and cloud condensation nuclei properties of the aerosol depend on the per-particle chemical species composition, or mixing state. Challenges arise in determining black carbon climate effects because the mixing state changes during the particles’ transport in the atmosphere. By condensation of semi-volatile substances, coagulation, and photochemical processes, termed aging, the mixing state of the particles change can further change. During the aging processes, initially hydrophobic black carbon become hydophilic, and can then act as cloud condensation nuclei. Under a high supersaturation, the particles can form cloud droplets, altering the cloud albedo and radiative forcing. To characterize the radiative effects of black carbon, knowledge of condensational growth and activation are important. In determining the particle evolution, it is necessary to consider entrainment of dry air into a cloud in order to achieve the cloud droplet spectra.In our current research, we used the particle-resolved model PartMC-MOSAIC, which has the ability to track the individual size and composition of thousands of particles through the aging processes of condensation, coagulation, and chemistry. Through PartMC-MOSAIC, an urban plume scenario was simulated and an aged particle population was determined every hour. Then, the particle populations were used as input into a particle-resolved cloud parcel model. Previously, the cloud parcel was assumed to be adiabatic. In this work, we tested the cloud parcel model capability with entrainment implemented through a homogeneousapproach.We presented three cases in this work. Case 1 used idealized temperature, pressure,and total specific humidity profiles to extend the study by Ching et al. (2012) to include entrainment. Case 2 used idealized total specific humidity profiles and less idealized temperature and pressure profiles, constructed from 3-D cloud resolving data. Finally, Case 3 used composition-averaged particle populations initialize the cloud parcel and we used Case 2 as a reference case to compare the results.For Case 1, entrainment caused a decrease in the cloud droplet number concentration (CDNC) and the liquid water content (LWC) according to the amount of entrainment. In Case 2, the CDNC and LWC followed the same pattern as Case 1 when using T2 profiles, while the CDNC was higher than the no entrainment case for the scenarios with T1 profiles. The size distribution broadened and shifted towards smaller sizes. In Case 3, a large overes- timation in the black carbon nucleation scavenged mass fraction, f_BC and a small difference in the cloud droplet fraction, f_N was seen for all plume hours in the compostition averaged case compared to the reference case. Entrainment altered f_BC and f_N for scenarios using T1 profiles.