China is challenged with the simultaneous goals of improving air quality and mitigating climate change. The “Beautiful China” strategy, launched by the Chinese government in 2020, requires that all cities in China attain 35 μg/m
3 or below for annual mean concentration of PM
2.5 (particulate matter with aerodynamic diameter less than 2.5 μm) by 2035. Meanwhile, China adopts a portfolio of low-carbon policies to meet its Nationally Determined Contribution (NDC) pledged in the Paris Agreement. Previous studies demonstrated the cobenefits to air pollution reduction from implementing low-carbon energy policies. Pathways for China to achieve dual targets of both air quality and CO
2 mitigation, however, have not been comprehensively explored. Here, we couple an integrated assessment model and an air quality model to evaluate air quality in China through 2035 under the NDC scenario and an alternative scenario (Co-Benefit Energy [CBE]) with enhanced low-carbon policies. Results indicate that some Chinese cities cannot meet the PM
2.5 target under the NDC scenario by 2035, even with the strictest end-of-pipe controls. Achieving the air quality target would require further reduction in emissions of multiple air pollutants by 6 to 32%, driving additional 22% reduction in CO
2 emissions relative to the NDC scenario. Results show that the incremental health benefit from improved air quality of CBE exceeds 8 times the additional costs of CO
2 mitigation, attributed particularly to the cost-effective reduction in household PM
2.5 exposure. The additional low-carbon energy polices required for China’s air quality targets would lay an important foundation for its deep decarbonization aligned with the 2 °C global temperature target.China is facing serious air pollution problems, particularly for ambient PM
2.5 (particulate matter with aerodynamic diameter less than 2.5 μm) which has harmful effects on human health (
1–
3). To protect human health, strengthened air pollution control policies were recently implemented in China targeting 35 μg⋅m
−3 or less for all cities by 2035 (
4). The Action Plan on Prevention and Control of Air Pollution, released in 2013, has resulted in noticeable reductions in urban ambient PM
2.5 concentrations (
5,
6). In 2018, however, China’s national PM
2.5 standard of 35 μg⋅m
−3 annual average was exceeded in 217 of China’s 338 cities at the prefecture or higher level, not to mention exceedance of the World Health Organization (WHO) guideline (annual mean PM
2.5 concentration <10 μg⋅m
−3). A big challenge for future improvement is that advanced end-of-pipe control technologies have already been widely applied in electric and industrial sectors (
7,
8). For example, over 90% of coal-fired power plants had installed end-of-pipe control technologies by 2018 (
8). Therefore, the potential for further reductions using end-of-pipe control measures might be limited, and implementation of low-carbon energy policies to constrain total energy consumption and promote a transition to clean energy is expected to be an inevitable option for further reducing air pollution (
9).The impacts of climate change on humans and ecosystems have also received considerable attention in China over the past few decades, and strategies for mitigating these impacts have been adopted (
10). In 2016, China officially signed its Nationally Determined Contribution (NDC) in the Paris Commitment, which pledges for CO
2 emissions per unit of GDP in 2030 to fall by 60 to 65% compared to 2005. A big concern arises as to whether China will continue its carbon reduction even under a pessimistic international situation after the US withdrawal from the Paris Agreement in 2019. Previous studies (
11–
18) have suggested that climate mitigation-oriented low-carbon energy policies can result in a reduction in air pollution.Therefore, there is a question as to whether China needs the application of low-carbon energy technologies and fuels to meet its air quality target. Such synergy is important, since many developing countries (e.g., China, India) are currently experiencing serious air pollution problems, and reducing air pollution is typically a more pressing national concern than climate mitigation (
19). This could lead to continuous reductions in CO
2 emissions even under a pessimistic international situation for mitigating climate change.Here, we project future air quality attainment in China through 2035, assess the CO
2 reduction cobenefits associated with attaining the ambient PM
2.5 standards, and evaluate the health and climate impacts associated with air quality attainment-oriented energy policies. We accomplish this by coupling an integrated assessment model [GCAM, the Global Climate Assessment Model (
20)], tuned with a detailed bottom-up emission inventory (
21), and an air quality model [CMAQ, the Community Multiscale Air Quality model (
22)] to evaluate future air quality and CO
2 emissions, and an integrated exposure−response (IER) model to evaluate the health effects due to the long-term ambient O
3 and both ambient and household PM
2.5 exposures in China. This integrated approach captures the nonlinearities among energy, emissions, concentrations, and health, thus allowing us to assess the cobenefits of air quality attainment on protecting health and mitigating CO
2 in an internally consistent framework.This study investigates future emissions of air pollutants and CO
2 in China under three future pathways with different considerations of two energy scenarios and two end-of-pipe control levels (). We first designed the NDC−current legislation (CLE) pathway to represent the CO
2 intensity reduction targets outlined by China’s NDC to meet the Paris Commitment (
23), with CLE level of end-of-pipe controls. This pathway represents the current ongoing energy policies and end-of-pipe control measures to be conducted in China following CLE. For the purpose of air quality attainment, we first designed the NDC−maximum feasible reduction (MFR) pathway to represent the same ongoing energy policies as the NDC−CLE scenario, but with MFR level realized by end-of-pipe controls. Additionally, to achieve the air quality attainment in 2035, we also introduce the CBE−MFR pathway, in which low-carbon energy policies beyond the NDC requirements are implemented (i.e., the cobenefit energy scenario [CBE]) with the MFR level of end-of-pipe controls.
Table 1.Design of future projection of air pollutant and CO
2 emissions
Pathway | Energy scenario | End-of-pipe control levels |
(1) NDC−CLE | Baseline scenario which considers only CO2 intensity reduction to meet the Paris Commitment* | CLE† |
(2) NDC−MFR | Same as energy scenario in NDC−CLE. | MFR‡ |
(3) CBE−MFR | Cobenefit energy scenario with implementation of low carbon policies related to energy conservation (e.g., improvement of energy efficiency)§ | MFR‡ |
Open in a separate window*The NDC scenario refers to the CLE of energy policies and plans conducted in China. Such an NDC scenario has a relatively conservative CO
2 target, as it only requires a peak in CO
2 emissions before 2030 and this has already been implemented in current Chinese plans. Following Fawcett et al. (
23), we set the CO
2 emissions to peak in 2030 at about 12 Gt (excluding agriculture and land use) and decrease by 4.5% every 5 y after 2030.
†At the CLE level, we assume that only the currently existing control policies are in place, including the Three-Year Action Plan for Winning the Blue Sky War from 2018 to 2020 and the 13th Five-Year Plan during 2015–2020. For example, the ultralow emission standard will be applied for all existing coal-fired units nationwide, and newly built coal-fired units in eastern China will be required to have emission rates equivalent to those of gas-fired units (
SI Appendix, Text S6). Furthermore, the ultralow emission standard will be implemented for key industries, including iron and steel, cement, plate glass, coking, nonferrous metal, and bricks (
SI Appendix, Text S7). Strengthened emission standards are also applied to the transportation sector, reducing total emissions from the transport fleet despite growing travel demand (
SI Appendix, Text S8). Advanced, low-emissions stoves will replace traditional household coal and biomass heating and cooking stoves in the commercial and household sector (
SI Appendix, Text S9).
‡At the MFR level, all of the feasible control policies will be applied to realize the maximal application of end-of-pipe controls. For example, desulfurization and denitrification efficiencies in coal-fired power plants reach their highest levels (99.0% and 91.5%, respectively) (
SI Appendix, Text S6); maximal application rates of advanced desulfurization, denitrification, and dedusting technologies are also applied in the industrial sector (
SI Appendix, Text S7); and advanced stoves with low emissions are fully adopted to replace traditional bulk coal and biomass use in the buildings (
SI Appendix, Text S9).
§The CBE scenario is designed for air quality attainment only, with no further constraints from the long-term climate goals (i.e., to meet the 2 °C global temperature target set out by Paris Agreement).Both energy scenarios are projected under the same future socioeconomic assumptions (
SI Appendix, Text S1), and their assumptions about low-carbon energy policies for the industry, building (i.e., residential and commercial), transportation, and electric sectors are detailed in
SI Appendix, Texts S2–S5, respectively. As presented in , the total energy uses in NDC and CBE in 2035 are estimated to be 150 and 126 exajoules (EJ), respectively. These values represent increases of 24% and 4%, respectively, from 2015, driven by the future growth of the economy and population (
SI Appendix, Fig. S1). The total CO
2 emissions in NDC and CBE are estimated as 11.3 and 8.8 Gt, respectively, in 2035. Two levels of end-of-pipe control are applied to the electricity, industry, transportation, and building and non−energy-related sectors, which are detailed in
SI Appendix, Texts S6–S9. The emission factors for PM
2.5, NOx (in terms of NO
2), and SO
2 have been greatly reduced with the application of end-of-pipe controls in 2035, compared to 2015 (). Note that the removal efficiencies of control technologies are less than 50% for domestic and agricultural sectors, which are difficult to control. The challenge to reducing the future emissions includes the continuous growth of activities (), as well as limited reduction potentials of end-of-pipe control measures (). For example, the end-of-pipe controls cannot be feasibly applied to domestic stoves. There are still over 200,000 industrial boilers which cannot be well controlled because current available end-of-pipe control techniques for small boilers have relatively lower SO
2 and NOx removal efficiency compared with power plants. In addition, the NMVOCs (nonmethane volatile organic compounds) and NH
3 emissions are very hard to control by current available end-of-pipe control technologies.
Open in a separate windowThe energy consumption in units of exajoules (EJ) and CO
2 emissions of two energy scenarios (
A) and emission factors in two end-of-pipe control levels (
B) compared with that in 2015.
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