Toward Clean Residential Energy: Challenges and Priorities in Research

Integrated Benefits of Synergistically Reducing Air Pollutants and Carbon Dioxide in China

China's advancements in addressing air pollution and reducing CO2 emissions offer valuable lessons for collaborative strategies to achieve diverse environmental objectives. Previous studies have assessed the mutual benefits of climate policies and air pollution control measures on one another, lacking an integrated assessment of the benefits of synergistic control attributed to refined measures. Here, we comprehensively used coupled emission inventory and response models to evaluate the integrated benefits and synergy degrees of various measures in reducing air pollutants and CO2 in China during 2013-2021. Results indicated that the implemented measures yielded integrated benefits value at 6.7 (2.4-12.6) trillion Chinese Yuan. The top five contributors, accounting for 55%, included promoting non-thermal power, implementing end-of-pipe control technologies in power plants and iron and steel industry, replacing residential scattered coal, and saving building energy. Measures demonstrating high synergies and integrated benefits per unit of reduction (e.g., green traffic promotion) yielded low benefits mainly due to their low application, which are expected to gain greater implementation and prioritization in the future. Our findings provide insights into the effectiveness and limitations of strategies aimed at joint control. By ranking these measures based on their benefits and synergy, we offer valuable guidance for policy development in China and other nations with similar needs.

Household fuel and direct carbon emission disparity in rural China

Universal access to clean fuels in household use is one explicit indicator of sustainable development while currently still billions of people rely on solid fuels for daily cooking. Despite of the recognized clean transition trend in general, disparities in household energy mix in different activities (e.g. cooking and heating) and historical trends remain to be elucidated. In this study, we revealed the historical changing trend of the disparity in household cooking and heating activities and associated carbon emissions in rural China. The study found that the poor had higher total direct energy consumption but used less modern energy, especially in cooking activities, in which the poor consumed 60 % more energy than the rich. The disparity in modern household energy use decreased over time, but conversely the disparity in total residential energy consumption increased due to the different energy elasticities as income increases. Though per-capita household CO2 and Black Carbon (BC) emissions were decreasing under switching to modern energies, the disparity in household CO2 and BC deepened over time, and the low-income groups emitted ∼ 10 kg CO2 more compared to the high-income population. Relying solely on spontaneous clean cooking transition had limited impacts in reducing disparities in household energy and carbon emissions, whereas improving access to modern energy had substantial potential to reduce energy consumption and carbon emissions and its disparity. Differentiated energy-related policies to promote high-efficiency modern heating energies affordable for the low-income population should be developed to reduce the disparity, and consequently benefit human health and climate change equally.

Identifying the fundamental drives behind the 10-year evolution of northern China's rural household energy and emission: Implications for 2030 and beyond

Rural household energy, particularly solid fuels, in northern China is thought to be a major source of air pollution. However, there is no complete, systematic, and reliable dataset for northern China's rural areas owing to the diversity of energy types used and the difficulty in acquiring data, particularly for solid fuels. Here we assessed existing progress in estimating solid fuels and proposed a practical route for deriving the information on rural household energy consumption and structure in northern China spanning 2010-2020, with important findings. (i) In 2010, the total rural household energy consumption for northern China was 287.51 million tons standard coal equivalent (TCE), while for 2020, it decreased to 205.14 million TCE, showing a 29 % decrease and an annual down 3.3 % averagely. Among a number of underlying reasons, China's urbanization process, which made the rural population shrink year by year, was primarily responsible. (ii) The share of clean energy in northern rural areas began at 4.2 % in 2010 and grew to 15.6 % in 2020, displaying a sustained improvement in energy structure. Particularly in the second 5 years, the clean energy share of policy priority areas grew by 20.0 percentage points (from 15.0 % in 2010 to 35.0 % in 2020), which is more than 18 percentage points higher than the growth of non-priority areas (from 2.9 % in 2010 to 4.5 % in 2020). Clean air policy, particularly the "two replacements" (replace coal with gas and electricity), in priority areas played a core role in changing the energy structure. (iii) Although both air pollutants and CO₂ are predicted to decrease in 2030, there is a large gap between expected 2030 emissions and hoped 2060 carbon neutrality in northern rural households. It is thus necessary to gradually boost the share of green electricity (non-fossil) and to reverse the trend of "biomass fuel curtailment" in rural residential sector. This calls for the improvement in biomass style (e.g., biomass pellets) and in stove efficiency (e.g., complete combustion).

Advances in technology and utilization of natural resources for achieving carbon neutrality and a sustainable solution to neutral environment

The greatest environmental issue of the twenty-first century is climate change. Human-caused greenhouse gas emissions are increasing the frequency of extreme weather. Carbon dioxide (CO₂) accounts for 80% of human greenhouse gas emissions. However, CO₂ emissions and global temperature have risen steadily from pre-industrial times. Emissions data are crucial for most carbon emission policymaking and goal-setting. Sustainable and carbon-neutral sources must be used to create green energy and fossil-based alternatives to reduce our reliance on fossil fuels. Near-real-time monitoring of carbon emissions is a critical national concern and cutting-edge science. This review article provides an overview of the many carbon accounting systems that are now in use and are based on an annual time frame. The primary emphasis of the study is on the recently created carbon emission and eliminating sources and technology, as well as the current application trends for carbon neutrality. We also propose a framework for the most advanced naturally available carbon neutral accounting sources capable of being implemented on a large scale. Forming relevant data and procedures will help the "carbon neutrality" plan decision-making process. The formation of pertinent data and methodologies will give robust database support to the decision-making process for the "carbon neutrality" plan for the globe. In conclusion, this article offers some opinions, opportunities, challenges and future perspectives related to carbon neutrality and carbon emission monitoring and eliminating resources and technologies.

Role of Peer Effects in China's Energy Transition: Evidence from Rural Beijing

China's efforts to encourage energy transition from coal to cleaner methods of space heating have gained great achievement. However, not all progress met expectations; that is, some households still rely on solid fuel. Sociocultural factors provide one plausible explanation. While existing studies have examined and quantified the socioeconomic factors, little attention has been paid to the peer effects that are often critical in the Chinese cultural context. This study first presents household energy consumption patterns using household-level data on the coal-switching program in rural Beijing. It shows that the coal-switching program did not completely eliminate the use of solid fuel for space heating as expected. To explore the underlying determinants, we apply an econometric model of the forces driving energy transition, focusing on peer effects. The results confirm that the coal-switching program significantly reduces the use of solid fuel. Moreover, it reveals that the peer effect, measured by the average village-level solid fuel use rate, matters for households' fuel choices. We also find that the peer effect varies with different income levels and policies. These findings provide new evidence and insights for future policy design.

Using the carbon balance method based on fuel-weighted average concentrations to estimate emissions from household coal-fired heating stoves

In China, household coal burning accounts for a large proportion of primary fine particulate matter (PM_2.5), black carbon (BC), organic carbon (OC), polycyclic aromatic hydrocarbons (PAHs) and carbon monoxide (CO) emissions. Previous field investigations generally measured short-term emissions from heating coal stoves, which did not provide a full characterization of the actual conditions in most cases, or resulted in large uncertainties in the calculated emission factors (EFs). In this study, we propose a sampling design using a chimney partial-capture dilution system in the field measurement of household coal-fired heating stoves emissions during selected periods within the different burn phases and then using the carbon balance method (CBM) based on fuel-weighted average concentrations (FWAC) from the different burn phases to quantify emissions. We evaluated this proposed methodology by comparing the results with a laboratory total-capture dilution-tunnel system. Statistical analysis indicated that emissions measured during the selected burn cycle periods using the dilution sampling system can generally represent emissions at different burn phases; however, different dilution ratios can affect EFs for PM_2.5 and OC. EFs of air pollutants derived by CBM with FWAC are more representative of the actual emissions than simple average concentration (SAC) and time-weighted average concentrations (TWAC). In the field application, to quantify FWAC, it is suggested to determine the ratio of power in the jth burn phase (P_j) to that in the high power phase (P_H) of the stove, i.e., P_j/P_H values with the calorimeter. If measured P_j/P_H values are not available, the recommended value in this study is also suggested.

Dynamic Evolution and Covariant Response Mechanism of Volatile Organic Compounds and Residual Functional Groups during the Online Pyrolysis of Coal and Biomass Fuels

Volatile organic compound (VOC) emissions from pyrolysis of widely used biomass are expected to increase significantly under the carbon neutrality target. However, the dynamic emissions and evolution mechanism of biomass-VOCs remain unclear, hindered by complex reactions and offline measurements. Here, we propose a novel covariant evolution mechanism to interpret the emission heterogeneities, sequential temperature responses, and evolved correlations of both VOCs and residual functional groups (RFGs) during corn straw (CS), wood pellet (WP), and semibituminous coal (SBC) pyrolysis. An innovative combination of online thermogravimetric-Fourier transform infrared-gas chromatography/mass spectrometry and two dimensional-correlation spectroscopy was applied. The relative percentages of CS/WP-VOCs were higher than those of SBC-VOCs, and most VOCs tended to have relatively small carbon skeletons as the average carbon oxidation state increased. With the temperature increased from low to high during CS/WP pyrolysis, the primary sequential response of VOCs (acids → phenols/esters → alcohols/ethers/aldehydes/ketones → hydrocarbons/aromatics) corresponded to the RFG response (hydroxyl groups → -CH₃/-CH₂-/-CH groups → aliphatic ethers and conjugated ketones). Compared with the relative regularity for CS/WP responses, the gas-solid products from SBC pyrolysis exhibited complex temperature-dependent responses and high oxidation-induced variability. These insights provide favorable strategies for the online monitoring system to facilitate priority removal of coal and biomass fuels-VOCs.

Real-World Emission Characteristics of Environmentally Persistent Free Radicals in PM2.5 from Residential Solid Fuel Combustion

Environmentally persistent free radicals (EPFRs) can induce reactive oxygen species, causing adverse health impacts, and residential fuel (biomass and coal) combustion is believed to be an important emission source for EPFRs; however, the residential emission characteristics of EPFRs are rarely studied in the real world. Here, we conducted a field campaign evaluating the presence and characteristics of EPFRs generated from residential biomass and coal burning in rural China. The emission factors (EFs) of EPFRs (with units of 10²⁰ spins·kg^-1) in PM_2.5 from the combustion of crop residues (3.97 ± 0.47) were significantly higher than those from firewood (2.06 ± 0.19) and coal (2.13 ± 0.33) (p < 0.05). The EPFRs from residential solid fuel combustion were carbon-centered free radicals adjacent to oxygen atoms. The fuel type was a primary factor controlling EPFR discharge, explaining 68% of the variation in EPFR EFs. The emissions from biomass burning had higher EPFRs per particle than those from coal combustion. EPFRs had stronger relationships with carbonaceous components than with other incomplete combustion products. The EPFRs from biomass burning were mostly generated during the pyrolysis of fuels, while the EPFRs generated from coal combustion were mainly associated with refractory organic compounds. This study provides valuable information for evaluating the fates of EPFRs, promoting a better understanding of the health impacts of air pollution.