Measure-Specific Effectiveness of Air Pollution Control on China's Atmospheric Mercury Concentration and Deposition during 2013-2017

Air pollutant emissions from coal-fired power plants in China over the past two decades

China is the largest coal producer and consumer in the world, and coal-fired power plants are among its major sources of air pollutants. The Chinese government has implemented various stringent measures to reduce air pollutant emissions over the past two decades. National statistical data, emission inventories, and satellite observations indicate that air pollutant emissions from coal-fired power plants have been effectively controlled. Field measurements at coal-fired power plants can provide valuable information about the long-term trend of air pollutant emissions and the driving factors. In this study, we evaluated air pollutant emissions from 401 units at 308 coal-fired power plants. An appreciable reduction in air pollutant concentrations and emission factors from coal-fired power plants in China is observed over the past two decades. The drivers for this trend from the perspective of policy making, application of removal technologies, tightening of emission standards, technological improvement, monitoring systems, and economic measures are discussed. Currently, concentrations of typical air pollutants from coal-fired power plants in China are lower than those in Japan, Germany, and the US. This can be attributed to the policies and lenient emission standards for power plants in these countries. The technological improvement of air pollution control devices is the key factor that has led to reductions in air pollutant emissions in China. China has built the largest system of clean coal-fired power plants in the world.

Enhanced H-abstraction contribution for oxidation of xylenes via mineral particles: Implications for particulate matter formation and human health

Xylenes are important aromatic hydrocarbons having broad industrial emissions and profound implication to air quality and human health. Generally, homogeneous atmospheric oxidation of xylenes is initiated by hydroxyl radical (OH) resulting in minor H-abstraction and major OH-addition pathways. However, the effect of mineral particles on the homogeneous atmospheric oxidation mechanism of xylenes is still not well understood. In the present study, the heterogeneous atmospheric oxidation of xylenes on mineral particles (TiO₂) is examined in detail. Both the experimental data and theoretical calculations are combined to achieve the feast. The experimental results detected a major H-abstraction (≥87.18%) and minor OH-addition (≤12.82%) pathways for the OH-initiated heterogeneous oxidation of three xylenes on TiO₂ under ultraviolet (UV) irradiation. Theoretical calculations demonstrated favorable H-abstraction on methyl group of xylenes by surface OH with large exothermic energies, because of the reason that their methyl group rather than the phenyl ring is more occupied by TiO₂ via hydrogen bonding. Furthermore, the particle monitor and acute risk assessment results indicated that the H-abstraction products significantly enhance the formation of particulate matter and health risk to human beings. Taken together, these results indicate that the atmospheric oxidation mechanism of xylenes is altered in the presence of mineral particles, highlighting the necessity to re-evaluate its implication in the environment and human health.

Atomically Dispersed Manganese on a Carbon-Based Material for the Capture of Gaseous Mercury: Mechanisms and Environmental Applications

A novel, atomically dispersed carbon-based sorbent was synthesized by anchoring manganese atoms with N atoms for the capture of gaseous elemental Hg (Hg⁰). Oxygen atoms were also introduced into the synthesis process to adjust the oxidizing ability of the Mn atoms. High-valence Mn (Mn⁴⁺) anchored by the O and N atoms (Mn-O/N-C) in the carbon-based materials provided more exposed active sites. The mercury removal efficiency of the composite exceeded 99%. The composite with a Mn loading of 0.9 wt % exhibited high affinity for Hg⁰, and the capacity for Hg⁰ adsorption within 275 min at room temperature reached 16.95 mg·g^-1. The Mn utilization was ∼56.61%, which is much larger than that of reported Mn-based oxide sorbents. The atomic-level distribution of Mn was well evidenced by aberration-corrected high-angle annular darkfield scanning transmission electron microscopy. Density functional theory calculations were conducted to evaluate the energy for adsorption of Hg⁰ on Mn-O/N-C. The results indicated that the amount of N and O atoms in the Mn coordination environment determined the Hg⁰ adsorption energy, and the presence of five optimized Mn adsorption structures in Mn-O/N-C was confirmed by Hg temperature-programmed desorption analysis. These materials may be utilized for mercury removal from disposal sites with high concentrations of mercury, broken mercury-containing lamps, or mercurial thermometers. The strategy of atomic dispersion during synthesis of the materials and adjusting the oxidizing ability in the single-atom strategy may be helpful for the development of environmentally benign functional materials.

Investigating the characteristics and source analyses of PM2.5 seasonal variations in Chengdu, Southwest China

In 2015, comprehensive observations were carried out in Chengdu, Sichuan Province, China, to elucidate the seasonal variation characteristics of the concentrations, chemical compositions, and the sources of PM_2.5 pollution. The meteorological parameters, gaseous pollutants and chemical compositions of PM_2.5 were measured. The annual average concentration of PM_2.5 in Chengdu was 67.44 ± 48.78 μg/m³. The highest seasonal PM_2.5 mass concentration occurred in winter with an average of 103.04 ± 66.76 μg/m³, followed by spring, autumn, and summer, and the wind speed had an important impact on the diffusion of PM_2.5. The seasonal variation characteristics of chemical components in PM_2.5 were analysed. The contribution and chemical conversion ability of secondary aerosols increased with increasing of PM_2.5 concentration. Source appointment of positive matrix factorization (PMF) shows that the main sources of PM_2.5 were secondary aerosols, coal combustion, biomass burning, vehicle emissions, dust and industrial sources, which have more obvious seasonal differences than other sources, and secondary aerosols and coal combustion were the major sources. Conditional probability function (CPF) analysis showed that the local sources of high PM_2.5 concentrations were mainly from the eastern and southeastern areas of Chengdu. Potential source contribution function (PSCF), concentration weighted trajectory (CWT) and backward trajectory cluster analyses indicated that the southern, southeast and eastern parts of the Sichuan Basin were the most likely potential sources of PM_2.5, and the unique geographical and topographical factors in Chengdu play important roles in the transport and diffusion of pollutants in this region.

Mercury Benefits of Climate Policy in China: Addressing the Paris Agreement and the Minamata Convention Simultaneously

National commitments under the Paris Agreement on climate change interact with other global environmental objectives, such as those of the Minamata Convention on Mercury. We assess how mercury emissions and deposition reductions from national climate policy in China under the Paris Agreement could contribute to the country's commitments under the Minamata Convention. We examine emissions under climate policy scenarios developed using a computable general equilibrium model of China's economy, end-of-pipe control scenarios that meet China's commitments under the Minamata Convention, and these policies in combination, and evaluate deposition using a global atmospheric transport model. We find climate policy in China can provide mercury benefits when implemented with Minamata policy, achieving in the year 2030 approximately 5% additional reduction in mercury emissions and deposition in China when climate policy achieves a 5% reduction per year in carbon intensity (CO₂ emissions 9.7 Gt in 2030). This corresponds to 63 Mg additional mercury emissions reductions in 2030 when implemented with Minamata Convention policy, compared to Minamata policy implemented alone. Climate policy provides emissions reductions in sectors not considered under the Minamata Convention, such as residential combustion. This changes the combination of sectors that contribute to emissions reductions.