Valuing the Air Quality Effects of Biochar Reductions on Soil NO Emissions

Effect of humic substances on nitrogen cycling in soil-plant ecosystems: Advances, issues, and future perspectives

Nitrogen (N) cycle is one of the most significant biogeochemical cycles driven by soil microorganisms on the earth. Exogenous humic substances (HS), which include composted-HS and artificial-HS, as a new soil additive, can improve the water retention capacity, cation exchange capacity and soil nutrient utilization, compensating for the decrease of soil HS content caused by soil overutilization. This paper systematically reviewed the contribution of three different sources of HS in the soil-plant system and explained the mechanisms of N transformation through physiological and biochemical pathways. HS convert the living space and living environment of microorganisms by changing the structure and condition of soil. Generally, HS can fix atmospheric and soil N through biotic and abiotic mechanisms, which improved the availability of N. Besides, HS transform the root structure of plants through physiological and biochemical pathways to promote the absorption of inorganic N by plants. The redox properties of HS participate in soil N transformation by altering the electron gain and loss of microorganisms. Moreover, to alleviate the energy crisis and environmental problems caused by N pollution, we also illustrated the mechanisms reducing soil N2O emissions by HS and the application prospects of artificial-HS. Eventually, a combination of indoor simulation and field test, molecular biology and stable isotope techniques are needed to systematically analyze the potential mechanisms of soil N transformation, representing an important step forward for understanding the relevance between remediation of environmental pollution and improvement of the N utilization in soil-plant system.

Evaluation of the Impact of Activated Biochar-Manure Compost Pellet Fertilizer on Volatile Organic Compound Emissions and Heavy Metal Saturation

For this experiment, pelletized activated biochar made of rice hullsor palm bark with swine manure compost was prepared to demonstrate the significant benefits of applying activated biochar-manure compost pellet fertilizer (ABMCP) inmitigating volatile organic compounds (VOCs), odor emission, and heavy metal saturation. Morphology and surface area analysis indicated that the activated rice hull biochar-manure compost pellet (ARP) had a significantly lower surface area, porous volume, and Fe content the activated palm biochar-manure compost pellet (APP). However, the ARP presented great potential to mitigate VOCs and odorant emissions. Our results indicated that the ARP reduced total reduced sulfur (TRS) and volatile fatty acids (VFAs) emissions by 69% and 93%, respectively. Heavy metals such as Pb, As, and Cd were not detected in the leachates fromthe ARP, APP, and swine manure compost. These results suggest that ABMCP can be a potential adsorbent to control VOCs and odorant emissions andpromote sustainable swine manure management and agricultural application.

Integrated Modeling of U.S. Agricultural Soil Emissions of Reactive Nitrogen and Associated Impacts on Air Pollution, Health, and Climate

Agricultural soils are leading sources of reactive nitrogen (Nr) species including nitrogen oxides (NO_x), ammonia (NH₃), and nitrous oxide (N₂O). The propensity of NO_x 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 NO_x 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.

Application of typical artificial carbon materials from biomass in environmental remediation and improvement: A review

Artificial carbon materials (ACMs), notably hydrochar, pyrochar, and artificial humic substances, etc., are considered to be sustainable and eco-friendly materials for environmental remediation and improvement. At present, almost relevant literature mainly focuses on biochar, and it is necessary to systematically summarize and expand studies on ACMs. ACMs are widely used to solve pollution problems in water and soil environments, as well as to remediate and improve soil quality. This review focuses on the following issues: 1. Reveal the synthetic mechanisms and compositional reactions effects of the charring process; 2. Define artificial humus as a novel class of ACMs and discuss the application of environmental remediation and relative enhancement effects; 3. Research the relative mechanisms and significance of ACMs during remediation process, involving removal and fixation of heavy metal ions (HMs)/organic pollutants (OPs), modification of soil physicochemical properties, affecting microbial community effects, and improving fertility for crop growth. Finally, the cost-benefit analysis and security-risk evaluation of ACMs are pointed out.

Potentials, Limitations, Co-Benefits, and Trade-Offs of Biochar Applications to Soils for Climate Change Mitigation

Biochar is one of the most affordable negative emission technologies (NET) at hand for future large-scale deployment of carbon dioxide removal (CDR), which is typically found essential to stabilizing global temperature rise at relatively low levels. Biochar has also attracted attention as a soil amendment capable of improving yield and soil quality and of reducing soil greenhouse gas (GHG) emissions. In this work, we review the literature on biochar production potential and its effects on climate, food security, ecosystems, and toxicity. We identify three key factors that are largely affecting the environmental performance of biochar application to agricultural soils: (1) production condition during pyrolysis, (2) soil conditions and background climate, and (3) field management of biochar. Biochar production using only forest or crop residues can achieve up to 10% of the required CDR for 1.5 ∘ C pathways and about 25% for 2 ∘ C pathways; the consideration of dedicated crops as biochar feedstocks increases the CDR potential up to 15–35% and 35–50%, respectively. A quantitative review of life-cycle assessment (LCA) studies of biochar systems shows that the total climate change assessment of biochar ranges between a net emission of 0.04 tCO 2 eq and a net reduction of 1.67 tCO 2 eq per tonnes feedstock. The wide range of values is due to different assumptions in the LCA studies, such as type of feedstock, biochar stability in soils, soil emissions, substitution effects, and methodological issues. Potential trade-offs between climate mitigation and other environmental impact categories include particulate matter, acidification, and eutrophication and mostly depend on the background energy system considered and on whether residues or dedicated feedstocks are used for biochar production. Overall, our review finds that biochar in soils presents relatively low risks in terms of negative environmental impacts and can improve soil quality and that decisions regarding feedstock mix and pyrolysis conditions can be optimized to maximize climate benefits and to reduce trade-offs under different soil conditions. However, more knowledge on the fate of biochar in freshwater systems and as black carbon emissions is required, as they represent potential negative consequences for climate and toxicity. Biochar systems also interact with the climate through many complex mechanisms (i.e., surface albedo, black carbon emissions from soils, etc.) or with water bodies through leaching of nutrients. These effects are complex and the lack of simplified metrics and approaches prevents their routine inclusion in environmental assessment studies. Specific emission factors produced from more sophisticated climate and ecosystem models are instrumental to increasing the resolution and accuracy of environmental sustainability analysis of biochar systems and can ultimately improve the characterization of the heterogeneities of varying local conditions and combinations of type feedstock, conversion process, soil conditions, and application practice.

Air quality and health benefits from potential coal power plant closures in Texas

As power production from renewable energy and natural gas grows, closures of some coal-fired power plants in Texas become increasingly likely. In this study, the potential effects of such closures on air quality and human health were analyzed by linking a regional photochemical model with a health impacts assessment tool. The impacts varied significantly across 13 of the state's largest coal-fired power plants, sometimes by more than an order of magnitude, even after normalizing by generation. While some power plants had negligible impacts on concentrations at important monitors, average impacts up to 0.5 parts per billion (ppb) and 0.2 µg/m³ and maximum impacts up to 3.3 ppb and 0.9 µg/m³ were seen for ozone and fine particulate matter (PM_2.5), respectively. Individual power plants impacted average visibility by up to 0.25 deciviews in Class I Areas. Health impacts arose mostly from PM_2.5 and were an order of magnitude higher for plants that lack scrubbers for SO₂. Rankings of health impacts were largely consistent across the base model results and two reduced form models. Carbon dioxide emissions were relatively uniform, ranging from 1.00 to 1.26 short tons/MWh, and can be monetized based on a social cost of carbon. Despite all of these unpaid externalities, estimated direct costs of each power plant exceeded wholesale power prices in 2016. Implications: While their CO₂ emission rates are fairly similar, sharply different NO_x and SO₂ emission rates and spatial factors cause coal-fired power plants to vary by an order of magnitude in their impacts on ozone, particulate matter, and associated health and visibility outcomes. On a monetized basis, the air pollution health impacts often exceed the value of the electricity generated and are of similar magnitude to climate impacts. This suggests that both air pollution and climate should be considered if externalities are used to inform decision making about power-plant dispatch and retirement.