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Background The design of highly active non-noble metal oxidation reduction catalysts (ORR) for microbial fuel cell (MFC) has always been a challenge. The aim of this study is to develop a highly active low cost cobalt-based ORR catalyst for MFCs cathode. Method Herein, a series of highly active nitrogen doped Co3O4-ZIF/Zn-T catalysts with different calcination temperatures (T) were prepared using bimetallic Co/Zn leaf blade structure Co-ZIF/Zn-67 as template. The Co3O4-ZIF/Zn-T catalysts were characterized by various methods, and the effect of T on the structure and ORR performance of MFC catalyst were studied. Significant findings The results showed that the Co3O4-ZIF/Zn-T derived from bimetallic Co/Zn leaf blade structure Co-ZIF/Zn-67 template exhibited better ORR performance than Co3O4-ZIF-400 derived from the dodecahedral structure Co-ZIF-67 template. The bimetallic Co/Zn Co-ZIF/Zn-67 template promotes more uniformly distributed mesopores, high N content and abundant smaller active Co3O4 sites due to its particular structure and the isolation effect of Zinc. Among Co3O4-ZIF/Zn-T catalysts, the Co3O4-ZIF/Zn-400 calcined at 400 °C demonstrated the highest ORR performance (onset potential was 0.082 V and MFC power density was 656.9 mw/m2), which was much higher than Co3O4-ZIF-400 (0.027 V and 402.8 mw/m2). The output voltage of MFC with Co3O4-ZIF/Zn-T exhibited no significant downward trend in 30 days stability test, indicating that the Co3O4-ZIF/Zn-400 catalyst has great stability.

The regional transport of air pollutants, controlled by emission sources and meteorological factors, results in a complex source–receptor relationship of air pollution change. Wuhan, a metropolis in the Yangtze River middle basin (YRMB) of central China, experienced heavy air pollution characterized by hourly PM2.5 concentrations reaching 471.1 µg m−3 in January 2016. To investigate the regional transport of PM2.5 over central eastern China (CEC) and the meteorological impact on wintertime air pollution in the YRMB area, observed meteorological and other relevant environmental data from January 2016 were analyzed. Our analysis presented noteworthy cases of heavy PM2.5 pollution in the YRMB area with unique “non-stagnant” meteorological conditions of strong northerly winds, no temperature inversion, and additional unstable structures in the atmospheric boundary layer. This unique set of conditions differed from the stagnant meteorological conditions characterized by near-surface weak winds, air temperature inversion, and stable structure in the boundary layer that are typically observed in heavy air pollution over most regions in China. The regional transport of PM2.5 over CEC aggravated PM2.5 levels, thus creating heavy air pollution in the YRMB area. This demonstrates a source–receptor relationship between the originating air pollution regions in CEC and the receiving YRMB region. Furthermore, a backward trajectory simulation using a Flexible Particle dispersion (FLEXPART) Weather Research and Forecasting (WRF) model to integrate the air pollutant emission inventory over China was used to explore the patterns of regional transport of PM2.5 governed by the strong northerly winds in the cold air activity of the East Asian winter monsoon season. It was estimated that the regional transport of PM2.5 from non-local air pollutant emissions contributes more than 65 % of the PM2.5 concentrations to the heavy air pollution in the YRMB region during the study period, revealing the importance of the regional transport of air pollutants over China as a causative factor of heavy air pollution over the YRMB area.

Regional transport of air pollutants controlled by both emission sources and meteorological factors results in a complex source-receptor relationship of air pollution change. Wuhan, a metropolis in the Yangtze River Middle Basin (YRMB) of central China experienced heavy air pollution characterized by excessive PM2.5 concentrations reaching 471.1 μg m−3 in January 2016. In order to investigate the regional transport of PM2.5 over China and the meteorological impact on wintertime air pollution in the YRMB area, observational meteorological and other relevant environmental data from January 2016 were analyzed. Our analysis presented the noteworthy cases of heavy PM2.5 pollution in the YRMB area with the unique “non-stagnant” meteorological conditions of strong northerly winds, no temperature inversion and additional unstable structures in the atmospheric boundary layer. This unique set of conditions differed from the stagnant meteorological conditions characterized by near-surface weak winds, air temperature inversion, and stable structure in the boundary layer observed in heavy air pollution over most regions in China. The regional transport of PM2.5 over central-eastern China aggravated PM2.5 levels present in the YRMB area, thus demonstrating the source-receptor relationship between the originating air pollution regions in central-eastern China and the receiving YRMB regions. Furthermore, a backward trajectory simulation using FLEXPART-WRF to integrate the air pollutant emission inventory over China was used to explore the patterns of regional transport of PM2.5 governed by the strong northerly winds in the cold air activity of the East Asian winter monsoon over central-eastern China, which contributes markedly to the heavy PM2.5 pollution in the YRMB area. It was estimated that the regional transport of PM2.5 of non-local air pollutant emissions could contribute more than 65 % of the PM2.5 concentrations to the heavy air pollution in the YRMB region during the study period, revealing the importance of the regional transport of air pollutants over central-eastern China in the formation of heavy air pollution over the YRMB region.

Since the 1980s, an industrial development has bloomed in China including the Yunnan–Guizhou Plateau (YGP), a remote region in Southwest China. To analyze the regional variations in air quality over YGP during the industrial development, we adopt the equivalent visibility by excluding the influence of natural factors on the observed visibility based on the meteorological data observed at 203 sites over YGP from 1980 to 2010 in this study. The YGP air quality exhibits the tremendous spatial differences in a general distribution from western good to eastern poor air quality. A similar pattern shifts seasonally in the spatial distribution with a typical seasonality of air quality over YGP between summertime low air pollution and wintertime high air pollution. The increasing and decreasing trends in visibility are mostly concentrated, respectively, in the YGP regions with high and low visibility, displaying the phenomenon of polarization in air quality change over YGP during 1980–2010. The regional mean visibility of the YGP presents a significant declining trend with change rate of −1.5 km decade−1 for air quality deterioration. The seasonal differences in visibility between summer (33.6 km) and winter (25.2 km) became obscure with the interannual change trends of visibility with stronger declines (−2.29 km decade−1) in summer and weaker decreases (−0.89 km decade−1) in winter over 1980–2010, which lead to a indistinct seasonality of air quality change over YGP. The remote YGP had experienced more frequent haze pollution, especially in the eastern plateau over 31 years. In accompany of increasing energy consumption in the industrial development, population growth is an important factor influencing the interannual change of YGP air quality. The distinct spatial distribution in the YGP terrain exerts an impact on poor air quality in lower flatlands harbored by mountainous topography with good air quality. Declined monsoon winds could meteorologically drive the air quality change with less regional transport of air pollutant over YGP during 1980–2010. Implications of the climate change for atmospheric environment will be having potential utility for sustainable development in China.

Various particulate matters (PM) and associated carbonaceous aerosols released from open biomass burning (including open straw burning, grass and forest fires) are major sources of atmospheric pollutants. Northeast China is a central region with high forest and grass coverage, as well as an intensive agricultural area. In this study, the FINN (Fire INventory from Ncar) emission data was used to analyze the spatiotemporal variations of PM and associated carbonaceous aerosol component (PM2.5, PM10, OC and BC) emissions from open biomass burning in Northeast China from 2002 to 2016. The results show that the total amount of annual PM2.5, PM10, OC and BC emissions was estimated to be 59.0, 70.6, 31.5, and 4.3 kilotons, respectively, from open biomass burning over Northeast China, averaged from 2002 to 2016, with significant inter-annual variations in amplitudes from 28.0 to 122.3, 33.7 to 144.1, 15.0 to 65.0, and 2.1 to 8.6 kilotons. The regional PM2.5, PM10, OC and BC emissions showed significant seasonal variations with highest emissions in spring (with a seasonal peak in April), followed by autumn (with a seasonal peak in October), summer, and winter in Northeast China, high emissions were concentrated in the forests and grasslands with natural fires, as well as over agricultural areas with crop straw burning from human activities. The PM2.5, PM10, OC and BC emissions over forest areas presented decreasing trends, while the emissions over farmlands showed increasing trends in Northeast China during 2002&ndash, 2016, this reflects on the dominance of biomass burning that shifted from forestland with natural fires to farmlands with increasing human activities. Three key meteorological drivers&mdash, strong near-surface wind speed, high air temperature and low relative humidity&mdash, were identified as having significant positive impacts on the inter-annual variations of PM2.5, PM10, OC and BC emissions from open biomass burning in Northeast China.