Browsing by Author "Luo, Lina"

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    Agroecosystem modeling of reactive nitrogen emissions from U.S. agricultural soils with carbon amendments
    (Springer Nature, 2023) Luo, Lina; Cohan, Daniel S.; Masiello, Caroline A.; Lychuk, Taras E.; Gao, Xiaodong
    Fertilizer-intensive agriculture is a leading source of reactive nitrogen (Nr) emissions that damage climate, air quality, and human health. Biochar has long been studied as a soil amendment, but its influence on Nr emissions remains insufficiently characterized. More recently, the pyrolysis of light hydrocarbons has been suggested as a source of hydrogen fuel, resulting in a solid zero-valent carbon (ZVC) byproduct whose impact on soil emissions has yet to be tested. We incorporate carbon amendment algorithms into an agroecosystem model to simulate emission changes in the year following the application of biochar or ZVC to the US. fertilized soils. Our simulations predicted that the impacts of biochar amendments on Nr emissions would vary widely (− 17% to + 27% under 5 ton ha−1 applications, − 38% to + 18% under 20 ton ha−1 applications) and depend mostly on how nitrification is affected. Low-dose biochar application (5 ton ha−1) stimulated emissions of all three nitrogen species in 75% of simulated agricultural areas, while high-dose applications (20 ton ha−1) mitigated emissions in 76% of simulated areas. Applying zero-valent carbon at 20 ton ha−1 exhibited similar effects on nitrogen emissions as biochar applications at 5 ton ha−1. Biochar amendments are most likely to mitigate emissions if applied at high rates in acidic soils (pH < 5.84) with low organic carbon (< 55.9 kg C ha−1) and inorganic nitrogen (< 101.5 kg N ha−1) content. Our simulations could inform where the application of carbon amendments would most likely mitigate Nr emissions and their associated adverse impacts.
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    Integrated Modeling of Agricultural Reactive Nitrogen in the United States: Emissions, Impacts, and Mitigation Strategies
    (2023-08-10) Luo, Lina; Cohan, Daniel S
    Fertilizer-intensive agriculture is a leading source of reactive nitrogen (Nr) emissions, including nitric oxide (NO), nitrous acid (HONO), and ammonia (NH3), that damage air quality, climate, and human health. As air pollutants, NO and NH3 contribute to the formation of ozone (O3) and particulate matter (PM), with impacts that depend on spatiotemporally variable atmospheric conditions. However, N2O, as a potent greenhouse gas, has climate impacts that are independent of when and where it is emitted. Additionally, the impacts of control strategies on Nr emissions vary widely and may introduce trade-off effects. Therefore, there is a strong need for a comprehensive assessment that considers the emissions, impacts, and mitigation strategies for Nr. I established an integrated assessment framework that connects a process-based agroecosystem model with reduced-complexity air quality and health models, along with the social cost of greenhouse gas. This framework enables us to consistently estimate Nr emissions, spatially track their contributions to air pollution, jointly quantify the associated damages using monetized damages as the metric, and assess the efficacy of control strategies. I applied this framework to investigate Nr emissions from U.S. croplands, their associated adverse impacts, and their responses to two mitigation strategies: carbon amendments and nitrification inhibitors (NIs). This study revealed that the Nr emissions are highest in regions with intensive fertilizer use. NH3 is the most damaging, especially in densely populated regions. Impacts of carbon amendments on Nr emissions would vary widely, with net effects depending mostly on how nitrification is affected. Biochar amendments are most likely to mitigate emissions if applied at high rates in acidic soils with low organic carbon and inorganic nitrogen content. Adding NIs to fertilizers can mitigate N2O and NO emissions but inadvertently stimulate NH3 emissions. Impacts of NIs are largest in regions with moderate soil temperatures. Net impacts of NIs would be negative across most regions as the health harms from NH3 stimulation outweigh the benefits of N2O and NO mitigation. This study provides valuable insights into Nr emissions mitigation. However, the current agroecosystem model, enhanced with carbon amendments and NIs algorithms, needs more field measurements for further evaluation and refinement.
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    Integrated Modeling of U.S. Agricultural Soil Emissions of Reactive Nitrogen and Associated Impacts on Air Pollution, Health, and Climate
    (American Chemical Society, 2022) Luo, Lina; Ran, Limei; Rasool, Quazi Z.; Cohan, Daniel S.
    Agricultural soils are leading sources of reactive nitrogen (Nr) species including nitrogen oxides (NOx), ammonia (NH3), and nitrous oxide (N2O). The propensity of NOx and NH3 to generate ozone and fine particulate matter and associated impacts on health are highly variable, whereas the climate impacts of long-lived N2O are independent of emission timing and location. However, these impacts have rarely been compared on a spatially resolved monetized basis. In this study, we update the nitrogen scheme in an agroecosystem model to simulate the Nr emissions from fertilized soils across the contiguous United States. We then apply a reduced-form air pollution health effect model to assess air quality impacts from NOx and NH3 and a social cost of N2O to assess the climate impacts. Assuming an $8.2 million value of a statistical life and a $13,100/ton social cost of N2O, the air quality impacts are a factor of ∼7 to 15 times as large as the climate impacts in heavily populated coastal regions, whereas the ratios are closer to 2.5 in sparsely populated regions. Our results show that air pollution, health, and climate should be considered jointly in future assessments of how farming practices affect Nr emissions.