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Atmospheric compositions and acid rain are closely related to atmospheric environment, weather, and climate change. In this study, the concentration levels and long-term trends of CO2, CH4, O3, PM2.5, PM10, and acid rain were presented at the Mt. Waliguan global baseline station in Qinghai, Shangdianzi and Lin'an regional background stations in the North China Plain (NCP) and the Yangtze River Delta region (YRD) of China based on the data observed until 2018. Significant increasing trends of CO2 were found at all of these stations. At Mt. Waliguan, the concentration levels and growth rate were consistent with the average values in the Northern Hemisphere (NH) and those observed at the Mauna Loa station in Hawaii. The CH4 also showed a upward tendency similar to that observed in NH. Compared with the observations at Mt. Waliguan global baseline station, the CO2 and CH4 mole fractions were higher at Shangdianzi and Lin'an regional background stations, indicating the important contributions of anthropogenic activities to the regional background level of CO2 and CH4. The annual averaged surface ozone showed increasing trends at Mt. Waliguan and Shangdianzi stations, whereas no clear trend was found at Lin'an station. Similar variations in the patterns of aerosol concentrations at Shangdianzi and Lin'an were found according to the PM2.5 or PM10 observations. Overall, the aerosol concentrations at both stations shown declining trends since the observations. However, two periods of high particle concentrations occurred in 2006–2007 and 2013–2014. The annual mean aerosol concentrations have continuously decreased after 2013–2014, indicating the effectiveness of pollution control in the NCP and YRD, especially since the implementation of the ‘Action Plan for Prevention and Control of Air Pollution’ in September 2013. Comparative analysis of aerosol with acid rain showed that the period with high concentrations of aerosols in the early years was consistent with that of severe acid rain pollution, suggesting that both aerosol pollution and severe acid rain are closely related to coal combustion emissions in China. As a result of the control of coal combustion emissions for acid and SO2, NOx emissions have contributed more substantially to aerosols due to the rapid growth of vehicle ownership. A comparison of the trends of aerosols with the maximum daily 8-h average of surface ozone (MDA8) at Shangdianzi and Lin'an stations revealed the complicated relationship between aerosol reduction and ozone production, i.e., together with the continuous improvement of particulate pollution in the NCP and YRD, the MDA8 at both stations showed a decreasing trend at first but subsequently increased after 2014 with aerosols remaining reduced. Such different variation patterns of the MDA8 with PM2.5 (or PM10) indicated the high challenge of synergic control of aerosol and ozone pollution in China.

A new method of extracting regional background concentration of CO2 in Yangtze River Delta was established based on the observations of both black carbon concentration and meteorological parameters. The concentrations of CO2 and black carbon were observed at Lin'an regional background station from 2009 to 2011. The regional background concentration of CO2 in Yangtze River Delta was obtained by means of this new method, and the impact of human activities on CO2 concentration in this area was also assessed. The results showed that the regional background concentration of CO2 extracted by this approach was comparable to the values obtained by R statistical filter method, and moreover this new method was better at picking up episodes heavily polluted by anthropogenic emissions. The annual regional average background concentration of CO2 in Yangtze River Delta from 2009 to 2011 was approximately 404.7 ± 8.2 ppm, 405.6 ± 5.3 ppm and 407.0 ± 5.3 ppm, respectively, much higher than global average value, indicating the distinct characteristic of this region. The anthropogenic emissions from Yangtze River Delta had significant influence on the concentration of CO2, increasing the value roughly 9.1 ppm higher than the regional background concentration of this area. [ABSTRACT FROM AUTHOR]