4 research outputs found

    Can Switching from Coal to Shale Gas Bring Net Carbon Reductions to China?

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    To increase energy security and reduce emissions of air pollutants and CO<sub>2</sub> from coal use, China is attempting to duplicate the rapid development of shale gas that has taken place in the United States. This work builds a framework to estimate the lifecycle greenhouse gas (GHG) emissions from China’s shale gas system and compares them with GHG emissions from coal used in the power, residential, and industrial sectors. We find the mean lifecycle carbon footprint of shale gas is about 30–50% lower than that of coal in all sectors under both 20 year and 100 year global warming potentials (GWP<sub>20</sub> and GWP<sub>100</sub>). However, primarily due to large uncertainties in methane leakage, the upper bound estimate of the lifecycle carbon footprint of shale gas in China could be approximately 15–60% higher than that of coal across sectors under GWP<sub>20</sub>. To ensure net GHG emission reductions when switching from coal to shale gas, we estimate the breakeven methane leakage rates to be approximately 6.0%, 7.7%, and 4.2% in the power, residential, and industrial sectors, respectively, under GWP<sub>20</sub>. We find shale gas in China has a good chance of delivering air quality and climate cobenefits, particularly when used in the residential sector, with proper methane leakage control

    Global Methane Emissions from Pit Latrines

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    Pit latrines are an important form of decentralized wastewater management, providing hygienic and low-cost sanitation for approximately one-quarter of the global population. Latrines are also major sources of the greenhouse gas methane (CH<sub>4</sub>) from the anaerobic decomposition of organic matter in pits. In this study, we develop a spatially explicit approach to account for local hydrological control over the anaerobic condition of latrines and use this analysis to derive a set of country-specific emissions factors and to estimate global pit latrine CH<sub>4</sub> emissions. Between 2000 and 2015 we project global emissions to fall from 5.2 to 3.8 Tg y<sup>–1</sup>, or from ∼2% to ∼1% of global anthropogenic CH<sub>4</sub> emissions, due largely to urbanization in China. Two and a half billion people still lack improved sanitation services, however, and progress toward universal access to improved sanitation will likely drive future growth in pit latrine emissions. We discuss modeling results in the context of sustainable water, sanitation, and hygiene development and consider appropriate technologies to ensure hygienic sanitation while limiting CH<sub>4</sub> emissions. We show that low-CH<sub>4</sub> on-site alternatives like composting toilets may be price competitive with other CH<sub>4</sub> mitigation measures in organic waste sectors, with marginal abatement costs ranging from 57 to 944 /toncarbondioxideequivalents(CO<sub>2</sub>e)inAfricaand46to97/ton carbon dioxide equivalents (CO<sub>2</sub>e) in Africa and 46 to 97 /ton CO<sub>2</sub>e in Asia

    Long-Lived Species Enhance Summertime Attribution of North American Ozone to Upwind Sources

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    Ground-level ozone (O<sub>3</sub>), harmful to most living things, is produced from both domestic and foreign emissions of anthropogenic precursors. Previous estimates of the linkage from distant sources rely on the sensitivity approach (i.e., modeling the change of ozone concentrations that result from modifying precursor emissions) as well as the tagging approach (i.e., tracking ozone produced from specific O<sub>3</sub> precursors emitted from one region). Here, for the first time, we tag all O<sub>3</sub> precursors (i.e., nitrogen oxides (NO<sub><i>x</i></sub>), carbon monoxide (CO), and volatile organic compounds (VOCs)) from East Asia and explicitly track their physicochemical evolution without perturbing the nonlinear O<sub>3</sub> chemistry. We show that, even in summer, when intercontinental influence on ozone has typically been found to be weakest, nearly 3 parts per billion by volume (ppbv) seasonal average surface O<sub>3</sub> over North America can be attributed to East Asian anthropogenic emissions, compared with 0.7 ppbv using the sensitivity approach and 0.5 ppbv by tagging reactive nitrogen oxides. Considering the acute effects of O<sub>3</sub> exposure, approximately 670 cardiovascular and 300 respiratory premature mortalities within North America could be attributed to East Asia. CO and longer-lived VOCs, largely overlooked in previous studies, extend the influence of regional ozone precursors emissions and, thus, greatly enhance O<sub>3</sub> attribution to source region

    Vehicle Emissions as an Important Urban Ammonia Source in the United States and China

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    Ammoniated aerosols are important for urban air quality, but emissions of the key precursor NH<sub>3</sub> are not well quantified. Mobile laboratory observations are used to characterize fleet-integrated NH<sub>3</sub> emissions in six cities in the U.S. and China. Vehicle NH<sub>3</sub>:CO<sub>2</sub> emission ratios in the U.S. are similar between cities (0.33–0.40 ppbv/ppmv, 15% uncertainty) despite differences in fleet composition, climate, and fuel composition. While Beijing, China has a comparable emission ratio (0.36 ppbv/ppmv) to the U.S. cities, less developed Chinese cities show higher emission ratios (0.44 and 0.55 ppbv/ppmv). If the vehicle CO<sub>2</sub> inventories are accurate, NH<sub>3</sub> emissions from U.S. vehicles (0.26 ± 0.07 Tg/yr) are more than twice those of the National Emission Inventory (0.12 Tg/yr), while Chinese NH<sub>3</sub> vehicle emissions (0.09 ± 0.02 Tg/yr) are similar to a bottom-up inventory. Vehicle NH<sub>3</sub> emissions are greater than agricultural emissions in counties containing near half of the U.S. population and require reconsideration in urban air quality models due to their colocation with other aerosol precursors and the uncertainties regarding NH<sub>3</sub> losses from upwind agricultural sources. Ammonia emissions in developing cities are especially important because of their high emission ratios and rapid motorizations
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