We honor here Professor David Mauzerall, a pioneer in the fields of photochemistry and photobiology of porphyrins and chlorophylls in vitro and in vivo, on the occasion of his 95th birthday. Throughout his career at The Rockefeller University, he refined our understanding of how chlorophyll converts light energy into chemical energy. He exploited top-of-the-line laser technology in developing photoacoustics and a variety of other innovative experimental approaches. His experimental work and conceptual insights contributed greatly to our understanding of photosynthesis and the possible role of photosynthesis in the origin of life. His contributions include many landmark single-authored and collaborative papers, and his legacy includes the training of others who have become authorities themselves. After providing a brief description of his research accomplishments, we include tributes from several of his coworkers and his daughters highlighting their valuable experiences with David Mauzerall on this milestone birthday.

Hard-to-abate sectors emitted ~30% of global CO2 emissions in 2018. As the world’s largest producer of chemicals and steel, China’s mitigation efforts in these sectors are crucial. Here we examine the greenhouse gas mitigation and costs of co-producing steel and chemicals in China by extracting H2 and CO from steelmaking off-gas for chemical production and using a customized optimization model with a life-cycle assessment. Without carbon pricing, co-production reduces greenhouse gas emissions by 36 MtCO2eq yr−1 (−7%) and costs by 1.5 billion CNY per year (−1%) relative to independent production. A carbon price of 350 CNY per tCO2 enhances emissions and cost reductions to 113 MtCO2eq yr−1 (−22%) and 25.5 billion CNY per year (−10%), respectively. Furthermore, 60% of total emissions and cost reductions can be achieved via 24% of connections, ~50% of which are in Hebei, Henan, Shanxi and Shandong provinces. This study demonstrates the cost-effectiveness of using co-production to mitigate these hard-to-abate emissions and the importance of targeting critical connections to obtain the majority of reductions. Achieving a net-zero future requires that hard-to-abate sectors be addressed. Co-production offers an opportunity to mitigate chemical and steel sector emissions by extracting H2 and CO from steelmaking off-gas and using them for chemical syntheses. The authors examine carbon mitigation and costs of co-producing chemicals and steel in China.

Clean hydrogen has the potential to serve as an energy carrier and feedstock in decarbonizing energy systems, especially in "hard-to-abate" sectors. Although many countries have implemented policies to promote electrolytic hydrogen development, the impact of these measures on costs of production and greenhouse gas emissions remains unclear. Our study conducts an integrated analysis of provincial levelized costs and life cycle greenhouse gas emissions for all hydrogen production types in China. We find that subsidies are critical to accelerate low carbon electrolytic hydrogen development. Subsidies on renewable-based hydrogen provide cost-effective carbon dioxide equivalent (CO2e) emission reductions. However, subsidies on grid-based hydrogen increase CO2e emissions even compared with coal-based hydrogen because grid electricity in China still relies heavily on coal power and likely will beyond 2030. In fact, CO2e emissions from grid-based hydrogen may increase further if China continues to approve new coal power plants. The levelized costs of renewable energy-based electrolytic hydrogen vary among provinces. Transporting renewable-based hydrogen through pipelines from low- to high-cost production regions reduces the national average levelized cost of renewables-based hydrogen but may increase the risk of hydrogen leakage and the resulting indirect warming effects. Our findings emphasize that policy and economic support for nonfossil electrolytic hydrogen is critical to avoid an increase in CO2e emissions as hydrogen use rises during a clean energy transition.

Improving air quality amid rapid industrialization and population growth is a huge challenge for India. To tackle this challenge, the Indian government implemented the National Clean Air Programme (NCAP) to reduce ambient concentrations of particulate matter with diameters less than 2.5 mu m (PM2.5) and 10 mu m (PM10) in hundreds of non-attainment cities that failed to meet the national ambient air quality standards. Here we evaluate the efficacy of the NCAP using data from the national air quality monitoring network combined with regional model simulations. Our results show an 8.8% yr(-1) decrease in annual PM2.5 pollution in the six non-attainment cities with continuous air pollution monitoring since 2017. Four of these six cities achieved over 20% reductions in PM2.5 pollution by 2022 relative to 2017, thereby meeting the NCAP target. However, we find that similar to 30% of the annual PM2.5 air quality improvements, and approximately half of the reductions during the heavily polluted winter months, can be attributed to favourable meteorological conditions that are unlikely to persist as the climate warms. Meanwhile, in 2022, annual PM2.5 levels in 44 out of 57 non-attainment cities with continuous monitors still failed to meet air quality standards. This work highlights the need for substantial additional mitigation measures beyond current NCAP policies to improve air quality in India.

Secondary inorganic aerosols play an important role in air pollution and climate change, and their formation modulates the atmospheric deposition of reactive nitrogen (including oxidized and reduced nitrogen), thus impacting the nitrogen cycle. Large-scale and long-term analyses of secondary inorganic aerosol formation based on model simulations have substantial uncertainties. Here we improve constraints on secondary inorganic aerosol formation using decade-long in situ observations of aerosol composition and gaseous precursors from multiple monitoring networks across the United States. We reveal a shift in the secondary inorganic aerosol formation regime in the rural United States between 2011 and 2020, making rural areas less sensitive to changes in ammonia concentrations and shortening the effective atmospheric lifetime of reduced forms of reactive nitrogen. This leads to potential increases in reactive nitrogen deposition near ammonia emission hotspots, with ecosystem impacts warranting further investigation. Ammonia (NH3), a critical but not directly regulated precursor of fine particulate matter in the United States, has been increasingly scrutinized to improve air quality. Our findings, however, show that controlling NH3 became significantly less effective for mitigating fine particulate matter in the rural United States. We highlight the need for more collocated aerosol and precursor observations for better characterization of secondary inorganic aerosols formation in urban areas. Chemical regimes of atmospheric secondary inorganic aerosol formation in rural areas of the United States shifted from NH3-sensitive to NH3-insensitive between 2011 and 2020, according to analyses of long-term observational data on aerosol composition and gaseous precursors.

Severe PM2.5 pollution threatens public health in India. Atmospheric stagnation traps emitted pollutants, worsening their health impacts. Global warming is anticipated to alter future stagnation patterns, impacting the effectiveness of air quality policies. Here, we develop a region-specific index that characterizes meteorological conditions driving stagnation and associated PM2.5 increases. Applying this index to an ensemble of climate models and global warming scenarios, we find that future stagnation changes result from both global CO2-driven circulation changes and local aerosol-driven meteorological responses. By 2100, we project an increase in winter stagnation in the Indo-Gangetic Plain (IGP) of 7 +/- 3 days that leads to an increase in PM2.5 of similar to 7ug/m(3) in a high-warming and high-aerosol scenario. However, annual stagnation occurrences decrease across most of India. Thus, stringent air quality regulations in the IGP during winters will be critical to reduce surface PM2.5 concentrations as climate warms. Such regulations will directly improve air quality while reducing future stagnation occurrences, providing additional air quality benefits.

Transport is a major contributor to carbon emissions and air pollution in China. Ongoing urbanization provides a unique opportunity for Chinese cities to abate emissions by reducing transport demand via compact urban development (CUD). Here we systematically evaluate the implications of CUD for climate, energy use, air quality and human health in 2050 China under various scenarios of alternative energy vehicle (AEV) deployment and power decarbonization. We find that, with low AEV penetration and carbon intensive power (57% coal + gas), ambitious CUD policy reduces on-road transport CO2 and NOx emissions by 97 Mt (8%) and 95 kt (7%), respectively, and avoids 25,000 premature deaths from ambient air pollution in 2050. CUD delivers less climate and air quality co-benefits as AEV penetration increases and their energy sources decarbonize, but continues to reduce vehicle energy use (up to 10%). With 100% AEV penetration, ambitious CUD policy still avoids 5,800 premature deaths by reducing non-exhaust vehicle emissions and upstream emissions. Our analysis demonstrates that CUD policy would provide considerable environmental and economic benefits in China. Rapid urbanization poses several challenges but can offer opportunities for cities to become more sustainable by, for example, reducing transport demand and its associated emissions. This study shows how this can be achieved and quantifies the co-benefits for climate, energy use, air quality and human health.

China’s clean heating policy since 2017 has notably improved air quality. However, the share of non-fossil sources in China’s urban district heating systems remain low, and many new coal-fired combined heat and power plants are being built. Strategic choices for district heating technologies are necessary for China to reach peak carbon emissions by 2030 and achieve carbon neutrality by 2060. Here we find that replacing polluting coal technologies with new and improved coal-fired combined heat and power plants will lead to substantial carbon lock-in and hinder decommissioning of associated coal-fired electricity generation. Expanding the use of industrial waste heat and air/ground-source heat pumps can avoid the need for new combined heat and power construction and reduce carbon emissions by 26% from 2020 to 2030. Our findings indicate the importance of the government’s recent proposals to decarbonize district heating. China’s continuing reliance on coal in district heating risks considerable carbon lock-in and hinders decommissioning of coal-fired electricity generation. This work outlines how the government can achieve its proposal to decarbonize district heating.

Battery storage is critical for integrating variable renewable generation, yet how the location, scale, and timing of storage deployment affect system costs and carbon dioxide (CO 2 ) emissions is uncertain. We improve a power system model, SWITCH-China, to examine three nationally uniform battery deployment strategies (Renewable-connected, Grid-connected, and Demand-side) and a heterogeneous battery deployment strategy where each province is allowed to utilize any of the three battery strategies. Here, we find that the heterogeneous strategy always provides the lowest system costs among all four strategies, where provinces with abundant renewable resources dominantly adopt Renewable-connected batteries while those with limited renewables dominantly adopt Demand-side batteries. However, which strategy achieves the lowest CO 2 emissions depends on carbon prices. The Renewable-connected strategy achieves the lowest CO 2 emissions when carbon prices are relatively low, and the heterogeneous strategy results in the lowest CO 2 emissions only at extremely high carbon prices.

Vehicle electrification is critical to enabling countries to develop more sustainably. Wider electric vehicle (EV) adoption relies on the deployment of EV charging stations (EVCSs). However, the local benefits associated with offering more charging opportunities to nearby residents remain unexplored. Here we provide empirical evidence on the impacts of proximate EVCSs on housing prices in California. We apply a hedonic property value approach using the EVCS data combined with about 14 million housing transaction records during 1993–2021. Our results show that access to charging infrastructure can be capitalized into property values. The average price premium for houses with EVCSs within 1 km is about 3.3% (or US$17,212) compared with homes without proximate EVCSs. The largest effect is a 5.8% increase for houses with EVCSs within 0.4–0.5 km compared with houses without proximate EVCSs. We find different results across neighbourhoods with diverse socio-demographic characteristics. Proximity to EVCSs increases traffic flows by 0.3–0.5% and lowers particulate matter (PM 2.5 ) emissions level by 1.3–2.2%. The increased property value after EVCS installation can incentivize the private real estate sector to expand the availability of charging services. More information on the housing price premium should be provided to facilitate the deployment of this sustainable infrastructure.

The development of urban transportation is affected by city population size, wealth, urban typology, the built environment, and fuel price, and has significant implications for urban sustainability. We analyze data of 297 Chinese cities between 2017 and 2019 using both simple regressions to examine the relationships between metrics of public and private transportation and city size, and multiple regressions to examine the impacts of the above urban factors on public transit use and private vehicle number. Both public transit use and private vehicle number scale super-linearly with population and sub-linearly with gross regional product. We find that the impacts of population size, city wealth, the built environment, and fuel price on transportation vary across city groups (industrial, mixed-economy, and commercial cities). We find that the relationships between urban transportation metrics and their factors extracted from intra-city variations over time are different from those derived from pooling data of multiple cities over time, indicating the importance of choosing appropriate analyses to inform local policymaking. A key finding is that to reduce private vehicle ownership, enhancing land use diversity, increasing rail transit, and expanding taxi fleets are more effective than increasing density in already dense Chinese cities. Our findings improve understanding of the drivers of public and private transportation in urban China which are needed to promote sustainable growth of Chinese cities.

Industrial parks are emerging priorities for carbon mitigation. Here we analyze air quality, human health, and freshwater conservation co-benefits of decarbonizing the energy supply of 850 China's industrial parks. We examine a clean energy transition including early retirement of coal-fired facilities and subsequent replacement with grid electricity and onsite energy alternatives (municipal solid waste-to-energy, rooftop photovoltaic, and distributed wind power). We find that such a transition would reduce greenhouse gas emissions by 41% (equal to 7% of 2014 national CO2 equivalent emissions); emissions of SO2 by 41%, NOx by 32%, and PM2.5 by 43% and freshwater consumption by 20%, relative to a 2030 baseline scenario. Based on modeled air pollutant concentrations, we estimate such a clean energy transition will result in ∼42,000 avoided premature deaths annually due to reduced ambient PM2.5 and ozone exposure. Costs and benefits are monetized including technical costs of changes in equipment and energy use and societal benefits resulting from improvements in human health and reductions of climate impacts. We find that decarbonizing industrial parks brings annual economic benefits of US$30-156 billion in 2030. A clean energy transition in China's industrial parks thus provides both environmental and economic benefits.

The United Kingdom government's National Atmospheric Emissions Inventory, used to provide UK greenhouse gas emission data to the United Nations Framework Convention on Climate Change, underestimates UK emissions from upstream oil and gas activities by approximately 80%.

Dietary shifts from staples toward meats, fruits, and vegetables increase environmental impacts. Excessive red meat intake and micro-nutrient deficiencies also raise health concerns. Previous research examined environmental and health consequences of alternative diets but overlooked impacts on air pollution and land use change. Here we examine implications of four potential Chinese dietary shifts on ammonia and particulate matter (PM2.5) air pollution, greenhouse gas (GHG) emissions, carbon storage loss associated with land-use change, water use, and human health. We show that a diet that replaces red meat with soy benefits the environment and avoids 57,000 PM2.5-related premature deaths annually. Dietary health benefits, however, appear larger with adoption of the Chinese Dietary Guideline (CDG) and EAT-Lancet diets, which prevent over one million premature deaths annually. However, both diets increase water use and GHGs. CDG also increases land use change, but EAT-Lancet reduces it by cutting dairy and red meat. Complex benefits and trade-offs of dietary shifts emphasize the need for further improvements in agricultural management to enable larger health-environment co-benefits.

China is now one of the world’s largest financiers and investors in the global electric power sector. While a number of important qualitative analyses have examined the determinants of Chinese energy finance, this paper deploys new data to perform the first econometric analysis to examine the determinants of Chinese overseas financing for electric power plants. Drawing on that earlier work, we examine a number of ‘push factors’ –incentives in China that facilitate investment abroad—and ‘pull factors’ –incentives in recipient countries that facilitate Chinese investment into their country. On the push side, we find that domestic overcapacity in China plays a key role in facilitating China’s development finance in these plants. On the pull side, we find that the size of local demand for new power projects and the resource potential for electric power in recipient countries are significantly correlated with the size of Chinese financing. We also find existing Chinese involvement in past power projects likely facilitates new Chinese overseas financing.

In 2017, the Chinese government launched a clean heating campaign that replaced millions of rural coal stoves with various clean heaters. The clean heating program contributed to remarkable improvements in air quality. However, the benefits of reducing heating demand by improving building envelope efficiency were not sufficiently considered. This study provides a needed quantitative assessment of potential energy-savings, costs, greenhouse gas emission reductions, and adoption strategies for improving building envelope efficiency in Chinese rural residential buildings. We find that different strategies must be employed in existing and new buildings to achieve desired outcomes. For existing buildings, to encourage easy and beneficial building retrofits (e.g., air sealing, efficient windows), current fuel subsidies should be replaced with retrofit subsidies. Building retrofits can reduce the size and hence capital costs of new clean heaters. They can also reduce operating costs, hence reducing the likelihood of backsliding to coal. For new construction, whole-home insulation and heat pumps would best avoid carbon lock-in. These efficient technologies have high upfront costs but decrease heating costs and significantly reduce carbon emissions relative to current policies. Hence, subsidies and policies that encourage improvements in building envelopes as well as the uptake of clean and efficient heaters are critical.

Symbiotic infrastructure systems facilitate deep decarbonization and efficient water use more than independent improvements in each type of infrastructure. Here we analyse strategies for bridging the coal power and wastewater treatment sectors in China by using sludge and reclaimed water from municipal wastewater treatment as alternative fuels and water sources for coal power generation. We develop a geodatabase covering ~2,400 coal-fired power plants and ~4,200 municipal wastewater treatment plants and conduct an integrated analysis using a customized optimization algorithm and life-cycle assessment. Such infrastructure symbiosis annually offers greenhouse gas (GHG) mitigation of 8.6 Mt CO 2 equivalent, equal to 29% and 0.28% of GHG emissions from the wastewater treatment and coal power sectors, respectively. The symbiosis annually conserves 3.0 billion m 3 of freshwater, equal to 62% of freshwater consumption by the coal power sector, and provides annual cost savings of 7.5 (3.4–12) billion CNY. Hebei, Shandong, Henan, Jiangsu, Zhejiang, Anhui and Guangdong contribute ~50% of GHG mitigation and ~60% of both freshwater conservation and cost savings due to the proximity of coal power and wastewater treatment plants. Approximately 80% of carbon, water and economic benefits can be achieved via 32% and 44% of all the plant-level linkages for sludge co-combustion and water reuse, respectively. Infrastructure symbiosis provides promising opportunities for both environmental and economic benefits. Policies to boost the establishment of energy–water infrastructure symbiosis would cost-effectively facilitate the achievement of China’s climate and water targets.

Worldwide efforts to switch away from coal have increased the reliance on natural gas imports for countries with inadequate domestic production. In preparing for potential gas import disruptions, there have been limited attempts to quantify the environmental and human health impacts of different options and incorporate them into decision-making. Here, we analyze the air pollution, human health, carbon emissions, and water consumption impacts under a set of planning strategies to prepare for potentially fully disrupted natural gas imports in China. We find that, with China's current natural gas storage capacity, compensating for natural gas import disruptions using domestic fossil fuels (with the current average combustion technology) could lead up to 23,300 (95% CI: 22,100-24,500) excess premature deaths from air pollution, along with increased carbon emissions and aggravated water stress. Improving energy efficiency, more progressive electrification and decarbonization, cleaner fossil combustion, and expanding natural gas storage capacity can significantly reduce the number of excess premature deaths and may offer opportunities to reduce negative carbon and water impacts simultaneously. Our results highlight the importance for China to increase the domestic storage capacity in the short term, and more importantly, to promote a clean energy transition to avoid potentially substantial environmental consequences under intensifying geopolitical uncertainties in China. Therefore, mitigating potential negative environmental impacts related to insecure natural gas supply provides additional incentives for China to facilitate a clean and efficient energy system transition.

Launched among growing concerns about air pollution in India, the National Clean Air Program (NCAP) 2019 aims to reduce PM2.5 concentrations by 20-30% by 2024, relative to 2017. This analysis is an overview of air pollution levels in India in the five years prior to implementation of the NCAP program and provides a baseline to evaluate its future success. We analyze ground observations from 2015 – 2019, of five criteria pollutants – PM10, PM2.5, SO2, NO2 and O3. We use data retrieved from the continuous and manual monitors across India to calculate annual average concentrations, seasonal cycles and monthly variability of these five pollutants in northern and southern India (divided at 23.5 oN). We find that northern India has (7%-129%) higher average concentrations of all pollutants compared with southern India, except for SO2 where the concentrations are similar. Particulate pollution dominates the pollution mix with virtually all sites in the northern region failing to meet the annual average PM10 and PM2.5 national ambient air quality standards (NAAQS) (of 60 g/m3 and 40 g/m3, respectively) while some sites in southern India meet the standard. Although inter-annual variability exists, no significant trend of these pollutant concentrations was observed over the five-year period. We also conduct case studies in five cities included in the US State Department Air-Now PM2.5 network - Delhi, Kolkata, Mumbai, Hyderabad and Chennai and include continuous monitoring data. We find the annual average PM10 and PM2.5 NAAQS concentrations to be frequently exceeded in these cities with highest concentrations found in Delhi, followed by Kolkata. SO2 concentrations, however, generally meet the NAAQS standard in all the five cities. NO2 NAAQS are exceeded in Delhi, Kolkata and Hyderabad in winter whereas O3 only occasionally exceeds NAAQS in Delhi. Our work creates a framework that can be used in future research to evaluate the success of the NCAP air pollution mitigation program.