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1. The driving effects of common atmospheric molecules for formation of clusters: the case of sulfuric acid, nitric acid, hydrochloric acid, ammonia, and dimethylamine

   https://doi.org/10.1039/D3EA00118K  

   Longsworth, Olivia M.; Bready, Conor J.; Joines, Macie S.; Shields, George C. (January 2023, Environmental Science: Atmospheres)

   Secondary aerosols form from gas-phase molecules that create prenucleation complexes, which grow to form aerosols. Understanding how secondary aerosols form in the atmosphere is essential for a better understanding of global warming. 

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2. Divergent global-scale temperature effects from identical aerosols emitted in different regions

   https://doi.org/10.1038/s41467-018-05838-6  

   Persad, Geeta G.; Caldeira, Ken (August 2018, Nature Communications)

   Abstract The distribution of anthropogenic aerosols’ climate effects depends on the geographic distribution of the aerosols themselves. Yet many scientific and policy discussions ignore the role of emission location when evaluating aerosols’ climate impacts. Here, we present new climate model results demonstrating divergent climate responses to a fixed amount and composition of aerosol—emulating China’s present-day emissions—emitted from 8 key geopolitical regions. The aerosols’ global-mean cooling effect is fourteen times greater when emitted from the highest impact emitting region (Western Europe) than from the lowest (India). Further, radiative forcing, a widely used climate response proxy, fails as an effective predictor of global-mean cooling for national-scale aerosol emissions in our simulations; global-mean forcing-to-cooling efficacy differs fivefold depending on emitting region. This suggests that climate accounting should differentiate between aerosols emitted from different countries and that aerosol emissions’ evolving geographic distribution will impact the global-scale magnitude and spatial distribution of climate change. 

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3. Simplified models of aerosol collision and deposition for disease transmission

   https://doi.org/10.1038/s41598-023-48053-0  

   Jung, Sunghwan Sunny (December 2023, Scientific Reports)

   Abstract Fluid-mechanics research has focused primarily on droplets/aerosols being expelled from infected individuals and transmission of well-mixed aerosols indoors. However, aerosol collisions with susceptible hosts earlier in the spread, as well as aerosol deposition in the nasal cavity, have been relatively overlooked. In this paper, two simple fluid models are presented to gain a better understanding of the collision and deposition between a human and aerosols. The first model is based on the impact of turbulent diffusion coefficients and air flow in a room on the collisions between aerosols and humans. Infection rates can be determined based on factors such as air circulation and geometry as an infection zone expands from an infected host. The second model clarifies how aerosols of different sizes adhere to different parts of the respiratory tract. Based on the inhalation rate and the nasal cavity shape, the critical particle size and the deposition location can be determined. Our study offers simple fluid models to understand the effects of geometric factors and air flows on the aerosol transmission and deposition. 

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4. Is Turning Down the Sun a Good Proxy for Stratospheric Sulfate Geoengineering?

   https://doi.org/10.1029/2020JD033952  

   Visioni, Daniele; MacMartin, Douglas G.; Kravitz, Ben (March 2021, Journal of Geophysical Research: Atmospheres)

   Abstract Deliberately blocking out a small portion of the incoming solar radiation would cool the climate. One such approach would be injecting SO₂into the stratosphere, which would produce sulfate aerosols that would remain in the atmosphere for 1–3 years, reflecting part of the incoming shortwave radiation. The cooling produced by the aerosols can offset the warming produced by increased greenhouse gas (GHG) concentrations, but it would also affect the climate differently, leading to residual differences compared to a climate not affected by either. Many climate model simulations of geoengineering have used a uniform reduction of the incoming solar radiation as a proxy for stratospheric aerosols, both because many models are not designed to adequately capture relevant stratospheric aerosol processes, and because a solar reduction has often been assumed to capture the most important differences between how stratospheric aerosols and GHG would affect the climate. Here we show that dimming the sun does not produce the same surface climate effects as simulating aerosols in the stratosphere. By more closely matching the spatial pattern of solar reduction to that of the aerosols, some improvements in this idealized representation are possible, with further improvements if the stratospheric heating produced by the aerosols is included. This is relevant both for our understanding of the physical mechanisms driving the changes observed in stratospheric‐sulfate geoengineering simulations, and in terms of the relevance of impact assessments that use a uniform solar dimming. 

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5. How Volcanic Aerosols Globally Inhibit Precipitation

   https://doi.org/10.1029/2023GL107930  

   McGraw, Zachary; Polvani, Lorenzo_M (June 2024, Geophysical Research Letters)

   Abstract Volcanic aerosols reduce global mean precipitation in the years after major eruptions, yet the mechanisms that produce this response have not been rigorously identified. Volcanic aerosols alter the atmosphere's energy balance, with precipitation changes being one pathway by which the atmosphere acts to return toward equilibrium. By examining the atmosphere's energy budget in climate model simulations using radiative kernels, we explain the global precipitation reduction as largely a consequence of Earth's surface cooling in response to volcanic aerosols reflecting incoming sunlight. These aerosols also directly add energy to the atmosphere by absorbing outgoing longwave radiation, which is a major cause of precipitation decline in the first post‐eruption year. We additionally identify factors limiting the post‐eruption precipitation decline, and provide evidence that our results are robust across climate models. 

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