Modeling Of Atmospheric Chemistry.pdf [HOT]

[Brianna Mccomas]

<div>SCOR (Scientific Committee on Oceanic Research) Working Group 167 (Reducing Uncertainty in Soluble aerosol Trace Element Deposition, RUSTED), appointed in October 2022, brings together experts from the atmospheric chemistry, ocean biogeochemistry, and modelling communities. Aiming to reduce uncertainties in soluble aerosol trace element deposition, RUSTED will quantitatively assess different aerosol leaching schemes; formulate standard operating procedures (SOPs) for frequently used aerosol leaching schemes; and develop a user-friendly, open-access database of aerosol trace element data which includes advice on the use of the data in Earth system models.</div><div></div><div></div><div>The American Meteorological Society/Environmental Protection Agency Regulatory Model Improvement Committee (AERMIC) was formed to introduce state-of-the-art modeling concepts into the EPA's air quality models. Through AERMIC, a modeling system, AERMOD, was introduced that incorporated air dispersion based on planetary boundary layer turbulence structure and scaling concepts, including treatment of both surface and elevated sources, and both simple and complex terrain. As of December 9, 2006, AERMOD is fully promulgated as a replacement to ISC3, in accordance with Appendix W (PDF)(54 pp, 761 K, 01-17-2017).</div><div></div><div></div><div></div><div></div><div></div><div>Modeling Of Atmospheric Chemistry.pdf</div><div></div><div>DOWNLOAD: https://t.co/jtsjlfT2zE </div><div></div><div></div><div>There are two input data processors that are regulatory components of the AERMOD modeling system: AERMET, a meteorological data preprocessor that incorporates air dispersion based on planetary boundary layer turbulence structure and scaling concepts, and AERMAP, a terrain data preprocessor that incorporates complex terrain using USGS Digital Elevation Data. Other non-regulatory components of this system include: AERSCREEN, a screening version of AERMOD; AERSURFACE, a surface characteristics preprocessor, and BPIPPRIM, a multi-building dimensions program incorporating the GEP technical procedures for PRIME applications.</div><div></div><div></div><div>For the current atmospheric conditions, reactive chlorine species originate from heterogenous reactions on sea-salt aerosols and other tropospheric aerosols, coal- and biomass-burning, and industrial activities13,14,15. Chlorine-containing species undergo photochemical reactions that produce chlorine atoms; the chlorine atom provides a direct sink towards CH4 (Eq. 2) and depletes O3 (Eq. 3; a critical source of tropospheric OH), therefore increasing CH4 loss via (Eq. 2) (Cl) but reducing CH4 loss via Eq. (1) (OH) (further details in Supplementary Text S1). A recent study showed that for present-day halogen abundance, chlorine together with iodine and bromine chemistry in the atmosphere decreases global CH4 loss, thus increasing CH4 lifetime, concentration, and radiative forcing16. However, the potential impacts of a significantly larger atmospheric chlorine burden on atmospheric composition, radiative forcing, and surface temperature remain unexplored.</div><div></div><div></div><div>This paper quantifies the globally averaged impact of additional chlorine emissions as a potential climate intervention technique. A homogeneous addition of chlorine species over all ocean surfaces may not be feasible in this respect but is chosen here as a pragmatic starting point. We consider a multitude of cases with different chlorine emissions but omit regional analysis to show a synthesis of the global impacts on atmospheric chemistry and climate. This includes analyzing the global change in atmospheric composition, both the intended change to CH4 and the unintended changes to other atmospheric constituents (mainly to OH, tropospheric O3, sulfate aerosol, stratospheric O3, and stratospheric water vapor), and determining the associated radiative forcing and surface temperature response to these changes. Additionally, we indicate the possible environmental impacts due to the addition of chlorine, including the impacts on air quality and ocean acidification. We identify several uncertainties in our modeling results. Finally, we propose an agenda for future research on this potential climate mitigation methodology.</div><div></div><div></div><div>The addition of chlorine modifies the global integrated burden of key short-lived climate forcers (SLCF; CH4, tropospheric O3, stratospheric H2O, and sulfate aerosol) (Fig. 3). The atmospheric CH4 burden is reduced by 20%, 45%, and 70% by year 2050 in the S630, S1250, and S1880 scenarios, respectively (Fig. 3). By the year 2050, the additional chlorine emissions also lead to lower tropospheric O3 by 25%, 40%, and 51%, and a reduction in stratospheric H2O by 21%, 34%, and 47%, respectively, for the three mitigation scenarios, as compared to RCP8.5. Lastly, the change in tropospheric OH results in decreased secondary sulfate aerosol production, mainly as a result of less SO2 conversion into H2SO4. Sulfate aerosol decreases by about 10% for all the mitigation scenarios compared to the RCP8.5 by mid-century. Other secondary aerosol types, such as secondary organic aerosol, change negligibly due to compensating effects between increased Cl atom and reduced OH. It is noteworthy that the chlorine-mediated relative change to all SLCFs stabilizes after about 15 years (the late 2030s) suggesting that the atmospheric system stabilizes at a new steady state after the chlorine additions (Fig. 3).</div><div></div><div></div><div>It is important to note that the pH of aerosols is not specifically calculated in CESM. The effect on the pH of aerosols of any of the proposed methods of increasing the reactive chlorine burden in the atmosphere, whether through directly emitting reactive chlorine, adding a substance that activates chlorine in aerosols, producing new SSA from the ocean, or any other method, is not clear. Pye et al.28 review the current state of atmospheric acidity and found that even drastic changes in sulfur dioxide and nitrogen oxide emissions across the US and Canada did not have a proportional effect on aerosol pH; on the other hand, clouds and fog exhibit a higher sensitivity to such changes. Further investigation is necessary for a more accurate analysis of the acidity change resulting from additional chlorine emissions.</div><div></div><div></div><div>Many questions need to be addressed in future studies to better understand the impacts of adding chlorine to reduce methane. We identify the following research questions as the most important to focus on: (1) How will future emission pathways change the impact of added chlorine? (2) What are the impacts of increased chlorine emissions on air quality? (3) What are the long-term ecosystem effects of additional chlorine emissions on acid deposition over land and ocean? (4) What is the environmental footprint (e.g., energy cost, CO2 emissions, etc.) of the production, transportation, and deployment stage necessary to increase the atmospheric chlorine burden? (5) Multi-model intercomparison studies should be conducted to investigate the impacts of various increased tropospheric chlorine burdens on atmospheric composition, climate, and the Earth system. (6) If the positive environmental effects overweight the negative environmental effects, how could we generate, transport, and release the quantity of chlorine studied here? (7) Where, how much, and when should chlorine emissions occur for maximum impact on climate and minimum environmental damage? An important part of future studies will be considerations of environmental justice.</div><div></div><div></div><div></div><div></div><div></div><div></div><div>We first conducted a 60-year spin-up (1960 to 2020) to ensure a stabilized atmospheric CH4 burden. From 2020 onward, we conducted a series of sensitivity cases with various emissions scenarios of additional molecular chlorine from the ocean surface worldwide. The emission flux of molecular chlorine is constant (in the unit of molecule/m2/s, therefore favoring total emissions in the tropical regions) on overall oceanic surfaces and during the entire simulation period (starting from 2020), without imposing any diurnal cycle. In this conceptual study, we do not link our modeling setup to any specific climate intervention technique method (e.g., via spraying iron salts or marine cloud brightening via sea-salt aerosol injection). Instead, we adopt a simple model setup to emit Cl2 over the global oceanic surface and quantify the global impacts of the increased chlorine burden on atmospheric composition and climate systems. We have taken the following considerations into account when assuming the additional chlorine is emitted over the ocean surface, instead of in the free troposphere or over land: (1) to allow a feasible emission method that does not require aircraft; (2) to reduce the energy cost and associated CO2 emissions required to emit chlorine; (3) to make full use of sea-salt aerosol, a natural chloride-containing atmospheric species prevalent in the marine boundary layer; (4) to reduce the potentially harmful effects on humans (over land); (5) to reduce the injected amount of chlorine to the stratosphere.</div><div></div><div></div><div>Table S1 in the supplement shows the setup of the standard simulations and sensitivity cases. The names of the sensitivity cases are defined as the added molecular chlorine flux. The difference in various species between RCP8.5 and the sensitivity cases represent the impact of these additional chlorine sources on atmospheric composition. Two more scenarios under the RCP6.0 case were also added to show a possible range of the additional molecular chlorine impacts under different climate scenarios.</div><div></div><div></div><div>Management strategies for controlling anthropogenic mercury emissions require understanding how ecosystems will respond to changes in atmospheric mercury deposition. Process-based mathematical models are valuable tools for informing such decisions, because measurement data often are sparse and cannot be extrapolated to investigate the environmental impacts of different policy options. Here, we bring together previously developed and evaluated modeling frameworks for watersheds, water bodies, and food web bioaccumulation of mercury. We use these models to investigate the timescales required for mercury levels in predatory fish to change in response to altered mercury inputs. We model declines in water, sediment, and fish mercury concentrations across five ecosystems spanning a range of physical and biological conditions, including a farm pond, a seepage lake, a stratified lake, a drainage lake, and a coastal plain river. Results illustrate that temporal lags are longest for watershed-dominated systems (like the coastal plain river) and shortest for shallow water bodies (like the seepage lake) that receive most of their mercury from deposition directly to the water surface. All ecosystems showed responses in two phases: A relatively rapid initial decline in mercury concentrations (20-60% of steady-state values) over one to three decades, followed by a slower descent lasting for decades to centuries. Response times are variable across ecosystem types and are highly affected by sediment burial rates and active layer depths in systems not dominated by watershed inputs. Additional research concerning watershed processes driving mercury dynamics and empirical data regarding sediment dynamics in freshwater bodies are critical for improving the predictive capability of process-based mercury models used to inform regulatory decisions.</div><div></div><div> dd2b598166</div>