排放

排放清单是空气质量模拟与分析的重要数据输入。哈佛大学中国项目从清华大学招收了一批博士后研究员来开发自下而上的排放清单，以便研究排放趋势、不确定度和防控政策。这项工作目前正由当年这批博士后中的赵瑜和王海鲲（两位现任南京大学环境学院教授）领衔在中国开展，从城市到全国尺度改善并应用排放清单，以达成多项研究目标。

如果没有相关化学物质的准确排放数据及其空间分布的具体信息，就不可能对大气浓度和通量进行准确模拟。这是开展可观测验证的模拟实验以进行污染防控方案分析的重要一环。一般而言，中国各省区的每种化学物质排放都是基于活动水平(能源消费水平或者工业生产水平)、排放因子、以及排放控制技术的去除效率来计算的。排放因子表述为每单位燃料燃烧后排出污染物的质量，或者在进行排放控制之前每单位工业生产排放污染物的质量。

同时为本大气排放研究项目做出贡献的学者还包括：哈佛大学中国项目访问学者王书肖教授(清华大学)和杨晴教授(华中科技大学)。本项大气排放研究项目，同其他关于大气化学模拟和大气实地观测研究项目一起，是哈佛大学中国项目中国大气排放控制与能源政策综合成本效益评估工作中的核心元素。

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声明：此处援引的部分论文出自美国国家科学基金会(NSF)ATM-1019134号或ATM-0635548号基金赞助项目(被引用论文中已注明)。这些论文中表达的任何观点、结论或建议均为作者本人观点，不代表美国国家科学基金会(NSF)的立场。

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Yu Zhao, Yutong Wang, Yiming Liu, Yueqi Jiang, Bo Zheng, Jia Xing, Yang Liu, Shuai Wang, and Chris Nielsen. 2023. “Sustained emission reductions have restrained the ozone pollution over China.” Nature Geoscience. Publisher's Version Abstract

Near-surface ozone pollution, associated with complex responses to changing precursor emissions and meteorological conditions, has become one of the biggest challenges in China’s air quality management. Here, we present the spatiotemporal evolution of ozone concentrations from 2010 to 2021 using measurements of the national air quality monitoring network. We evaluate the effectiveness of the national air pollution control programme, including Phase 1 (2013–2017) and Phase 2 (2018–2021), in reducing the ozone level over China, using an optimized machine learning approach, high-resolution emission estimates and an improved air quality model. We find that while emission changes in Phase 1 increased the ozone level over the five highly developed regions, further reductions of nitrogen oxide emissions in Phase 2 have generally constrained the ozone pollution. The changing effect of emission controls on ozone pollution is due to the shift in the prevailing regime for ozone formation and the weakened effects of aerosol declines, as emission reductions continue. We further find that current emission controls have been more effective in rural locales in four of the five regions, and more effective in summer than winter. Therefore, further control of ozone pollution should consider these regional and seasonal variations to identify the most important precursors for the pollution.

Xi Yang, Chris P. Nielsen, Shaojie Song, and Michael B. McElroy. 2022. “Breaking the “hard-to-abate” bottleneck in China’s path to carbon neutrality with clean hydrogen.” Nature Energy. Publisher's Version Abstract

Countries such as China are facing a bottleneck in their paths to carbon neutrality: abating emissions in heavy industries and heavy-duty transport. There are few in-depth studies of the prospective role for clean hydrogen in these ‘hard-to-abate’ (HTA) sectors. Here we carry out an integrated dynamic least-cost modelling analysis. Results show that, first, clean hydrogen can be both a major energy carrier and feedstock that can significantly reduce carbon emissions of heavy industry. It can also fuel up to 50% of China’s heavy-duty truck and bus fleets by 2060 and significant shares of shipping. Second, a realistic clean hydrogen scenario that reaches 65.7 Mt of production in 2060 could avoid US$1.72 trillion of new investment compared with a no-hydrogen scenario. This study provides evidence of the value of clean hydrogen in HTA sectors for China and countries facing similar challenges in reducing emissions to achieve net-zero goals.

Peter Sherman, Haiyang Lin, and Michael B. McElroy. 2022. “Projected global demand for air conditioning associated with extreme heat and implications for electricity grids in poorer countries.” Energy and Buildings. Publisher's Version Abstract

Human-induced climate change will increase surface temperatures globally over the next several decades. Climate models project that global mean surface temperature could increase by over 2˚C by 2050 relative to the preindustrial period, with even greater changes at the regional level. These temperature changes have clear and pertinent implications for extremes, and consequentially, heat-induced health issues for people living in particularly hot climates. Here, we study future projections in the demand for AC globally in the 2050s associated with extreme heat events. To do this, we employ an ensemble of CMIP6 models under high and low emissions scenarios. We find that the increasing frequency of extreme temperatures will cause a significant portion of the global population to be exposed to conditions that require cooling. This issue will be especially pervasive in poor countries such as India and Indonesia, which at present lack the AC units required to handle rapidly growing populations and increased frequencies of extreme temperatures. The electricity needed for cooling in these countries could reach as high as 75% of the current total annual electricity demand, which could place serious strain on the electricity grid infrastructure during peak cooling hours. We conclude that demand for cooling in the future will pose a significant challenge for poorer countries whose people will require AC units to handle extreme temperatures. In some countries, the grid infrastructure is insufficient at present to meet projected AC demands, and this need must be considered in future power systems planning.

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