Analysis of China's PM2.5 and ozone coordinated control strategy based on the observation data from 2015 to 2020.

The coordinated control of PM2.5 and ozone has become the strategic goal of national air pollution control. Considering the gradual decline in PM2.5 concentration and the aggravation of ozone pollution, a better understanding of the coordinated control of PM2.5 and ozone is urgently needed. Here, we collected and sorted air pollutant data for 337 cities from 2015 to 2020 to explore the characteristics of PM2.5 and ozone pollution based on China's five major air pollution regions. The results show that it is necessary to continue to strengthen the emission reduction in PM2.5 and ozone precursors, and control NOx and VOCs while promoting a dramatic emission reduction in PM2.5. The primary method of curbing ozone pollution is to strengthen the emission control of VOCs, with a long-term strategy of achieving substantial emission reductions in NOx, because VOCs and NOx are also precursors to PM2.5; hence, their reductions also contribute to the reduction in PM2.5. Therefore, the implementation of a multipollutant emission reduction control strategy aimed at the prevention and control of PM2.5 and ozone pollution is the only means to realize the coordinated control of PM2.5 and ozone.

A comprehensive investigation on volatile organic compounds (VOCs) in 2018 in Beijing, China: Characteristics, sources and behaviours in response to O3 formation.

Observations of volatile organic compounds (VOCs) are a prerequisite for evaluating the effectiveness of government efforts targeting VOC pollution. Here, based on the one-year online VOC measurement in 2018 in Beijing, systematic analyses and model simulation were conducted to illuminate VOC characteristics, emission sources, regional hotspots and behaviours in response to O3 formation. The observed mean VOC concentration in 2018 was 29.12 ± 17.64 ppbv declined distinctly compared to that in 2015 and 2016. Vehicle exhaust (39.95%), natural gas/liquefied petroleum gas (22.04%) and industrial sources (20.64%) were the main contributors to VOCs in Beijing. Regional transport, mainly from the south-south-east (SSE) and south-south-west (SSW), quantitatively contributed 36.65%-55.06% to VOCs based on our developed method. O3 sensitivity tended to be in the transition regime in summer identified by ground-based and satellite observations. Strong solar radiation along with high temperature and low humidity aggravated O3 pollution that was further intensified by regional transport from southern polluted regions. The model simulation determined that turning off CH3CHO related reactions brought about the most predominantly short-term and long-run O3 reduction, indicating that control policies in VOC species should be tailored, instead of one-size-fits-all. Overall, region-collaborated and active VOC-species-focused strategies on VOC controls are imperative.

Characterization and sources of volatile organic compounds (VOCs) and their related changes during ozone pollution days in 2016 in Beijing, China.

Concentrations of 99 volatile organic compounds (VOCs) were continuously measured online at an urban site in Beijing, China, in January, April, July, and October 2016. Characterization and sources of VOCs and their related changes during days with heavy ozone (O3) pollution were analysed. The total observed concentration of VOCs (TVOCs) was 44.0 ± 28.9 ppbv. The VOC pollution level has decreased in Beijing but remains higher than in other Chinese cities. Alkanes comprised the highest proportion among seven major sampled VOC groups. The concentrations and sources of ambient VOCs showed obvious temporal variations. Six emission sources were identified by the positive matrix factorization (PMF), including biomass burning, coal combustion, gasoline vehicles, diesel vehicles, solvent usage, and biogenic + secondary emissions. The combustion source was the key control factor for VOC reduction in Beijing. From the potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) model, Beijing, Tianjin, Hebei, Shanxi, Inner Mongolia, Shandong, and Henan were identified as major potential source regions of ambient VOCs. O3 formation was sensitive to VOCs in Beijing according to the VOC/NOx ratio (ppbC/ppbv, 8:1 threshold). High- and low-O3 days in July were identified, and high O3 levels were due to both enhanced VOC emission levels and meteorological conditions favourable to the production of O3. These findings provide evidence that the fuel combustion and regional transport have a great impact on concentrations and sources of VOCs in urban Beijing.

Aerosol optical properties under different pollution levels in the Pearl River Delta (PRD) region of China.

To clarify the aerosol hygroscopic growth and optical properties of the Pearl River Delta (PRD) region, integrated observations were conducted in Heshan City of Guangdong Province from October 19 to November 17, 2014. The concentrations and chemical compositions of PM2.5, aerosol optical properties and meteorological parameters were measured. The mean value of PM2.5 increased from less than 35 (excellent) to 35-75 µg/m3 (good) and then to greater than 75 µg/m3 (pollution), corresponding to mean PM2.5 values of 24.9, 51.2, and 93.3 µg/m3, respectively. The aerosol scattering hygroscopic growth factor (f(RH = 80%)) values were 2.0, 2.12, and 2.18 for the excellent, good, and pollution levels, respectively. The atmospheric extinction coefficient (σext) and the absorption coefficient of aerosols (σap) increased, and the single scattering albedo (SSA) decreased from the excellent to the pollution levels. For different air mass sources, under excellent and good levels, the land air mass from northern Heshan had lower f(RH) and σsp values. In addition, the mixed aerosol from the sea and coastal cities had lower f(RH) and showed that the local sources of coastal cities have higher scattering characteristics in pollution periods.

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 PM2.5 pollution. The meteorological parameters, gaseous pollutants and chemical compositions of PM2.5 were measured. The annual average concentration of PM2.5 in Chengdu was 67.44 ±â€¯48.78 µg/m3. The highest seasonal PM2.5 mass concentration occurred in winter with an average of 103.04 ±â€¯66.76 µg/m3, followed by spring, autumn, and summer, and the wind speed had an important impact on the diffusion of PM2.5. The seasonal variation characteristics of chemical components in PM2.5 were analysed. The contribution and chemical conversion ability of secondary aerosols increased with increasing of PM2.5 concentration. Source appointment of positive matrix factorization (PMF) shows that the main sources of PM2.5 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 PM2.5 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 PM2.5, and the unique geographical and topographical factors in Chengdu play important roles in the transport and diffusion of pollutants in this region.

Enhanced photocatalytic reduction activity of uranium(vi) from aqueous solution using the Fe2O3-graphene oxide nanocomposite.

Photocatalytic technologies are a potential solution for remediation of radioactive wastewater, including the reduction of radioactive hexavalent uranium, which is commonly found in wastewater from the nuclear industry. In this study, Fe2O3-graphene oxide composites were synthesized by an easy and scalable impregnation method as a catalyst for the reduction of U(vi). X-ray photoelectron spectroscopy analysis and high-resolution transmission electron microscopy images of this composite clearly showed that the Fe2O3 nanoparticles exist in the layered structure of graphene oxide. The photocatalytic activity of the Fe2O3-graphene oxide composite was evaluated by the reduction of U(vi) to U(iv) in aqueous solution under visible light. The results showed that the photocatalytic process of the Fe2O3-graphene oxide composite was always faster than that of the Fe2O3 nanoparticles. Moreover, the experimental kinetic data for the catalytic process followed a pseudo-first-order model. The stability of the Fe2O3-graphene oxide composites was studied over successive experiments, with the photocatalytic reduction efficiency of U(vi) decreasing to 76.0% after four cycles. Based on these experimental results, the enhanced photocatalytic activity and stability of Fe2O3-graphene oxide composites can be attributed to the improved adsorption properties of U(vi) at GO and the electron transfer from iron oxide to GO.