The coronavirus disease 2019 (COVID-19) pandemic has upended almost every facet of academia (1). Almost overnight the system faced a sudden transition to remote teaching and learning, changes in grading systems, and the loss of access to research resources. Additionally, shifts in household labor, childcare, Many women academics will likely bear a greater burden during the coronavirus disease 2019 (COVID-19) pandemic. Academia needs to enact solutions to retain and promote women faculty who already face disparities regarding merit, tenure, and promotion. Image credit: Dave Cutler (artist).
Abstract. Ice-nucleating particles (INPs) are known to affect the amount of ice in mixed-phase clouds, thereby influencing many of their properties. The atmospheric INP concentration changes by orders of magnitude from terrestrial to marine environments, which typically contain much lower concentrations. Many modelling studies use parameterizations for heterogeneous ice nucleation and cloud ice processes that do not account for this difference because they were developed based on INP measurements made predominantly in terrestrial environments without considering the aerosol composition. Errors in the assumed INP concentration will influence the simulated amount of ice in mixed-phase clouds, leading to errors in top-of-atmosphere radiative flux and ultimately the climate sensitivity of the model. Here we develop a global model of INP concentrations relevant for mixed-phase clouds based on laboratory and field measurements of ice nucleation by K-feldspar (an ice-active component of desert dust) and marine organic aerosols (from sea spray). The simulated global distribution of INP concentrations based on these two species agrees much better with currently available ambient measurements than when INP concentrations are assumed to depend only on temperature or particle size. Underestimation of INP concentrations in some terrestrial locations may be due to the neglect of INPs from other terrestrial sources. Our model indicates that, on a monthly average basis, desert dusts dominate the contribution to the INP population over much of the world, but marine organics become increasingly important over remote oceans and they dominate over the Southern Ocean. However, day-to-day variability is important. Because desert dust aerosol tends to be sporadic, marine organic aerosols dominate the INP population on many days per month over much of the mid- and high-latitude Northern Hemisphere. This study advances our understanding of which aerosol species need to be included in order to adequately describe the global and regional distribution of INPs in models, which will guide ice nucleation researchers on where to focus future laboratory and field work.
<p><strong>Abstract.</strong> Ice nucleating particles (INP) are known to affect the amount of ice in mixed-phase clouds, thereby influencing many of their properties. The atmospheric INP concentration changes by orders of magnitude from terrestrial to marine environments, which typically contain much lower concentrations. Many modelling studies use parameterizations for heterogeneous ice nucleation and cloud ice processes that do not account for this difference because they were developed based on measurements predominantly from terrestrial environments. Errors in the assumed INP concentration will influence the simulated amount of ice in mixed-phase clouds, leading to errors in top-of-atmosphere radiative flux and ultimately the climate sensitivity of climate models. Here we develop a global model of INP concentrations relevant for mixed-phase clouds based on laboratory and field measurements of ice nucleation by K-feldspar (an ice-active component of desert dust) and marine organic aerosols (from sea spray). The simulated global distribution of INP concentrations based on these two-species agrees much better with currently available ambient measurements than when INP concentrations are assumed to depend only on temperature or particle size. Underestimation of INP concentrations in some terrestrial locations may be due to neglect of INP from other terrestrial sources. Our model indicates that, on a monthly or yearly average basis, desert dusts dominate the contribution to the INP population over much of the world, but marine organics become increasingly important in the world's remote oceans and can dominate in the Southern Ocean at some time of the year. Furthermore, we show that day-to-day variability is important and since desert dust aerosol tends to be sporadic, marine organics dominate the INP population on many days per month in much of the mid and high latitude northern hemisphere. This study advances our understanding of which aerosol species need to be included in order to adequately describe the global and regional distribution of INP in models, which will guide ice nucleation researchers on where to focus future laboratory and field work.</p>
Abstract. Ice nuclei were measured in immersion-freezing mode in the eastern Mediterranean region using the FRIDGE-TAU (FRankfurt Ice-nuclei Deposition freezinG Experiment, the Tel Aviv University version) chamber. Aerosol particles were sampled during dust storms and on clean and polluted days (e.g., Lag BaOmer). The aerosol immersion-freezing potential was analyzed in the laboratory using a drop-freezing method. Droplets from all the samples were found to freeze between −11.8 • C and −28.9 • C. Immersion-freezing nuclei (FN) concentrations range between 0.16 L −1 and 234 L −1 , while the activated fraction (AF) ranges between 8.7 × 10 −8 and 4.9 × 10 −4 . The median temperature at which the drops from each filter froze was found to be correlated with the corresponding daily average of PM 10 , PM 2.5 and PM 10 -PM 2.5 . A higher correlation value between FN concentrations and PM 10 -PM 2.5 suggests that the larger particles are generally more effective as FN.The measurements were divided into dust storms and "clean" conditions (this is a relative term, because dust particles are always present in the atmosphere is this region) based on the air mass back trajectories and the aerosol mass concentrations (PM 10 ). Droplets containing ambient particles from dust storm days froze at higher temperatures than droplets containing particles from clean days. Statistically significant differences were found between dust storms and clean conditions primarily in terms of the initial temperature at which the first drops froze, the median freezing temperature and the aerosol loading (PM values). FN concentrations and AF values in dust storms were larger by more than a factor of 2 than in the clean conditions. This observation agrees with previous studies showing that some dust particles are almost always present in the atmosphere in this region.Measurements of aerosol particles emitted from wood burning bonfires during a Lag BaOmer holiday showed that although a high concentration of particles was emitted, those particles' effectiveness as FN was relatively poor. The most likely reason for the low FN efficiency is the combination of relatively low fire temperatures and high organic carbon fraction in the aerosols.
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