Impact of aerosol number concentration on precipitation under different precipitation rates

Abstract

Mainly by modifying the number concentration and size of cloud droplets, the dynamic and thermodynamic effects of aerosols are important in the formation of precipitation, but so far different and occasionally opposite responses of precipitation to aerosol concentration have been noted. By conducting two numerical experiments with different aerosol concentrations, the impact of aerosol number concentration on precipitation under different precipitation rates is examined. To this end, the Weather Research and Forecasting (WRF) model with a two‐moment aerosol‐aware bulk microphysical scheme was applied. Results indicate that mainly through redistribution of precipitation both spatially and temporarily, more hygroscopic aerosols in the atmosphere could potentially reduce light precipitation events, but increase heavy precipitation events. In regions with a high precipitation rate (> 1 mm/hr), an ample influx of water vapour exists. Thus, cloud droplets have no need to compete for water vapour in order to grow, which results in an enhancement of precipitation under the polluted atmosphere. On the other hand, less efficient autoconversion processes and/or increased cloud‐top evaporation may contribute to the decrease in light (< 0.6 mm/hr) to moderate (0.6–1 mm/hr) precipitation under the polluted atmosphere. A delay in the onset of precipitation is identified in the polluted experiment, which leads to a significant increase in precipitation rate, primarily due to more freezing of cloud droplets and extra release of latent heat of freezing, which invigorates cloud developments, while intensification of secondary clouds by aerosols might have also partly contributed.

Human-driven greenhouse gas and aerosol emissions cause distinct regional impacts on extreme fire weather

“…Interestingly, biomass burning aerosols have an opposite effect to industrial aerosols in some regions. For example, the Amazon region experiences an increase in extreme fire-weather risk in the early 21st century due to biomass burning, possibly linked to inhibited cloud formation, which reduces low-intensity precipitation and increases temperatures 33 , 34 . These findings establish a more nuanced characterization of the anthropogenic impact on extreme fire-weather risk to inform mitigation and adaptation strategies.…”

Adsorptive and Coagulative Removal of Trace Metals from Water Using Surface Modified Sawdust-Based Cellulose Nanocrystals

“…Control experiments were first conducted to confirm the precipitation of these metals before introducing the coagulant. It is reported that the rate of precipitation increased with an increase in dissolution rate as the solution became more concentrated [31]. Therefore, little or no reduction in the concentration of Cu and Pb were observed in the acidic medium up to pH 7.20; however, the removal efficiencies obtained from pH 7.20 to 10 might be due to dual mechanisms suggested to be precipitation and adsorption in Figure 5a,b.…”

On the contribution of fast and slow responses to precipitation changes caused by aerosol perturbations

“…ARC is the difference of shortwave (SW) and longwave (LW) fluxes between the top of the atmosphere (TOA) and the surface. ARC has significant impacts on global hydrological sensitivity (Allen and Ingram, 2002), while changes in the energy transport term (δH ) are essential in determining the spatial pattern of precipitation response (Muller and O'Gorman, 2011). Dagan et al (2019) further demonstrated that whether precipitation responses are more correlated with changes in Q or H depends on the latitude considered.…”

“…An energetic perspective provides an alternative approach to examine aerosol effects on precipitation, which is referred to as a "top-down" approach. For global scales, in equilibrium, latent heat released from rainfall should be energetically balanced by atmospheric radiative cooling together with surface energy fluxes (Allen and Ingram, 2002;Andrews et al, 2010). Climate forcers, such as greenhouse gases (GHGs) and aerosols, which affect the energy budget, can modify the hydrological responses (Kvalevåg et al, 2013;Stephens and Hu, 2010).…”