# Air Pollution, Greenhouse Gases & Climate

Shaojie Song, Athanasios Nenes, Meng Gao, Yuzhong Zhang, Pengfei Liu, Jingyuan Shao, Dechao Ye, Weiqi Xu, Lu Lei, Yele Sun, Baoxian Liu, Shuxiao Wang, and Michael B. McElroy. 2019. “Thermodynamic modeling suggests declines in water uptake and acidity of inorganic aerosols in Beijing winter haze events during 2014/2015–2018/2019.” Environmental Science & Technology Letters, 6, Pp. 752-760. Publisher's VersionAbstract
During recent years, aggressive air pollution mitigation measures in northern China have resulted in considerable changes in gas and aerosol chemical composition. But it is unclear whether aerosol water content and acidity respond to these changes. The two parameters have been shown to affect heterogeneous production of winter haze aerosols. Here, we performed thermodynamic equilibrium modeling using chemical and meteorological data observed in urban Beijing for four recent winter seasons and quantified the changes in the mass growth factor and pH of inorganic aerosols. We focused on high relative humidity (>60%) conditions when submicron particles have been shown to be in the liquid state. From 2014/2015 to 2018/2019, the modeled mass growth factor decreased by about 9%–17% due to changes in aerosol compositions (more nitrate and less sulfate and chloride), and the modeled pH increased by about 0.3–0.4 unit mainly due to rising ammonia. A buffer equation is derived from semivolatile ammonia partitioning, which helps understand the sensitivity of pH to meteorological and chemical variables. The findings provide implications for evaluating the potential chemical feedback in secondary aerosol production and the effectiveness of ammonia control as a measure to alleviate winter haze.
S.J. Song, M. Gao, W.Q. Xu, Y.L. Sun, D.R. Worsnop, J.T. Jayne, Y.Z. Zhang, L. Zhu, M. Li, Z. Zhou, C.L. Cheng, Y.B. Lv, Y. Wang, W. Peng, X.B. Xu, N. Lin, Y.X. Wang, S.X. Wang, J. W. Munger, D. Jacob, and M.B. McElroy. 2019. “Possible heterogeneous hydroxymethanesulfonate (HMS) chemistry in northern China winter haze and implications for rapid sulfate formation.” Atmospheric Chemistry and Physics, 19, Pp. 1357-1371. Publisher's VersionAbstract
The chemical mechanisms responsible for rapid sulfate production, an important driver of winter haze formation in northern China, remain unclear. Here, we propose a potentially important heterogeneous hydroxymethanesulfonate (HMS) chemical mechanism. Through analyzing field measurements with aerosol mass spectrometry, we show evidence for a possible significant existence in haze aerosols of organosulfur primarily as HMS, misidentified as sulfate in previous observations. We estimate that HMS can account for up to about one-third of the sulfate concentrations unexplained by current air quality models. Heterogeneous production of HMS by SO2 and formaldehyde is favored under northern China winter haze conditions due to high aerosol water content, moderately acidic pH values, high gaseous precursor levels, and low temperature. These analyses identify an unappreciated importance of formaldehyde in secondary aerosol formation and call for more research on sources and on the chemistry of formaldehyde in northern China winter.
Haikun Wang, Xi Lu, Yu Deng, Yaoguang Sun, Chris P. Nielsen, Yifan Liu, Ge Zhu, Maoliang Bu, Jun Bi, and Michael B. McElroy. 2019. “China’s CO2 peak before 2030 implied from diverse characteristics and growth of cities.” Nature Sustainability, 2, Pp. 748–754. Publisher's VersionAbstract

China pledges to peak CO2 emissions by 2030 or sooner under the Paris Agreement to limit global warming to 2 °C or less by the end of the century. By examining CO2 emissions from 50 Chinese cities over the period 2000–2016, we found a close relationship between per capita emissions and per capita gross domestic product (GDP) for individual cities, following the environmental Kuznets curve, despite diverse trajectories for CO2 emissions across the cities. Results show that carbon emissions peak for most cities at a per capita GDP (in 2011 purchasing power parity) of around US$21,000 (80% confidence interval: US$19,000 to 22,000). Applying a Monte Carlo approach to simulate the peak of per capita emissions using a Kuznets function based on China’s historical emissions, we project that emissions for China should peak at 13–16 GtCO2 yr−1 between 2021 and 2025, approximately 5–10 yr ahead of the current Paris target of 2030. We show that the challenges faced by individual types of Chinese cities in realizing low-carbon development differ significantly depending on economic structure, urban form and geographical location.

2019 Nov 14

# Driving and the Built Environment: Is Transit-Oriented Development Effective in Shanghai?

3:30pm to 4:45pm

## Location:

Pierce 100F, 29 Oxford Street, Cambridge

A Harvard-China Project Research Seminar with Faan Chen, Postdoctoral Fellow, Harvard-China Project, Paulson School of Engineering and Applied Sciences, Harvard University

Abstract: The rapid growth of cities such as Shanghai in China has presented many transportation, land use and climate change challenges for local government officials, planning and transit practitioners and property...

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Ying Wang, Bin Chen, Chenghe Guan, and Bo Zhang. 2019. “Evolution of methane emissions in global supply chains during 2000-2012.” Resources, Conservation and Recycling, 150, 104414. Publisher's VersionAbstract
Reduction of methane emissions (CH4) plays an important role in addressing global climate change. Most previous studies have focused on the direct CH4 emissions of economies, but overlooked the upstream CH4 emissions along global supply chains induced by the final consumption of economies. Using a global multi-regional input-output analysis, this study aims to explore the evolution of CH4 emissions embodied in international trade and final consumption in major economies during 2000–2012. The results show that China, the EU, USA, India and Brazil were the top five economies with high volumes of consumption-based CH4 emissions from 2000 to 2012. In particular, China’s consumption-based CH4 emissions showed an observable growth trend, while the EU, the USA and Japan showed a downward trend. It’s estimated that growing amounts of CH4 emissions (i.e., the volume increase from 77.1 Mt in 2000 to 95.9 Mt in 2012) were transferred globally via international trade, primarily as exports from China, Russia and other large developing economies to consumers in major developed economies. Russia–EU, China–USA and China–EU formed the main bilateral trading pairs of embodied emission flows. Further analysis found that per capita consumption-based CH4 emissions was closely related to their per capita GDP. Quantifying the CH4 emissions embodied in trade and final demand of major economies can provide important basis for understanding economy-wide emission drivers to design global and regional CH4 reduction scheme from a consumer perspective.
Wenjie Tian, Xudong Wu, Rong Ma, and Bo Zhang. 2019. “Quantifying global CH4 and N2O footprints.” Journal of Environmental Management, 251, 109566. Publisher's VersionAbstract
This study aims to quantify global CH4 and N2O footprints in 2012 in terms of 181 economies and 20 world regions based on the official national emission accounts from the UNFCCC database and the global multi-region input-output accounts from the EORA database. Global total CH4 and N2O emissions increased by 15.0% in 2012 compared to 1990, mainly driven by increasing demands of agricultural and energy products. Mainland China, Western Europe, the USA, Southeast Asia and Sub-Saharan Africa were identified as the largest five CH4 footprint contributors (55.6% of the global total), while Mainland China, the USA, Western Europe, Brazil and Sub-Saharan Africa as the largest N2O footprint contributors (59.2% of the global total). In most developed economies, the CH4 and N2O footprints were much higher than their emissions on the production side, but opposite picture is observed in emerging economies. 36.4% and 24.8% of the global CH4 and N2O emissions in 2012 were associated with international trade, respectively. Substantial energy-related CH4 and agricultural CH4 and N2O emissions were transferred from developed countries to developing countries. Several nations within Kyoto targets have reduced their CH4 and N2O emissions significantly between 1990 and 2012, but the generally-believed success is challenged when viewing from the consumption side. Mainland China, Southeast Asia, Sub-Saharan Africa, Brazil, Middle East and India witnessed prominent increase of CH4 and N2O footprints in the same period. The structure and spatial patterns of global CH4 and N2O footprints shed light on the role of consumption-side actions and international cooperation for future non-CO2 GHG emission reduction.
2019 Oct 24

# Characteristics and Mixing State of Haze Pollution in China

3:30pm to 4:45pm

## Location:

Pierce 100F, 29 Oxford Street, Cambridge

A China Project Research Seminar with Fengkui Duan, Associate Professor, School of Environment, Tsinghua University, China.

She earned her PhD in Environmental Science and Engineering from Tsinghua University. Her research concerns air pollution and its control, focusing on...

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2019 Oct 03

# Social Costs of Air Pollution in China

3:30pm to 4:45pm

## Location:

Pierce 100F, 29 Oxford Street, Cambridge

A China Project Research Seminar with Siqi ZHENG, the Samuel Tak Lee Associate Professor of Real Estate Development and Entrepreneurship in the MIT Department of Urban Studies and Planning, and the Faculty Director, MIT China Future City Lab....

# China May be on Track to Meet its CO2 Emissions Goals Early

August 13, 2019

Study finds that as cities become wealthier, per capita emissions drop

China, the world’s largest carbon emitter today, may be on track to meet its emission goals up to a decade early, according to a recent study on the cover of Nature Sustainability led by researchers from Nanjing University in Nanjing, China, and Harvard University.

The research focuses the relationship between urban economic growth and CO2 emissions. Fifty cities...

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Peter Sherman, Meng Gao, Shaojie Song, Patrick Ohiomoba, Alex Archibald, and Michael B. McElroy. 2019. “The influence of dynamics and emissions changes on China’s wintertime haze.” Journal of Applied Meteorology and Climatology, 58, Pp. 1603-1611. Publisher's VersionAbstract

Haze days induced by aerosol pollution in North and East China have posed a persistent and growing problem over the past few decades. These events are particularly threatening to densely-populated cities such as Beijing. While the sources of this pollution are predominantly anthropogenic, natural climate variations may also play a role in allowing for atmospheric conditions conducive to formation of severe haze episodes over populated areas. Here, an investigation is conducted into the effects of changes in global dynamics and emissions on air quality in China’s polluted regions using 35 simulations developed from the Community Earth Systems Model Large Ensemble (CESM LENS) run over the period 1920-2100. It is shown that internal variability significantly modulates aerosol optical depth (AOD) over China; it takes roughly a decade for the forced response to balance the effects from internal variability even in China’s most polluted regions. Random forest regressions are used to accurately model (R2 > 0.9) wintertime AOD using just climate oscillations, the month of the year and emissions. How different phases of each oscillation affect aerosol loading are projected using these regressions. AOD responses are identified for each oscillation, with particularly strong responses from El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). As ENSO can be projected a few months in advance and improvements in linear inverse modelling (LIM) may yield a similar predictability for the PDO, results of this study offer opportunities to improve the predictability of China’s severe wintertime haze events, and to inform policy options that could mitigate subsequent health impacts.

2019 Jun 01

# CCICED Annual Meeting

Sat Jun 1 (All day) to Wed Jun 5 (All day)

## Location:

Hangzhou International Expo Center, Zhejiang Province, China

China Project faculty chair, Michael McElroy, who has been appointed to the China Council for International Cooperation on Environment and Development (CCICED) for a 5-year term, and Executive Director, Chris Nielsen, will be participating in the ...