Substantial nitrogen oxides emission reduction from China due to COVID-19 and its impact on surface ozone and aerosol pollution.

A top-down approach was employed to estimate the influence of lockdown measures implemented during the COVID-19 pandemic on NOx emissions and subsequent influence on surface PM2.5 and ozone in China. The nation-wide NOx emission reduction of 53.4% due to the lockdown in 2020 quarter one in China may represent the current upper limit of China's NOx emission control. During the Chinese New Year Holiday (P2), NOx emission intensity in China declined by 44.7% compared to the preceding 3 weeks (P1). NOx emission intensity increased by 20.3% during the 4 weeks after P2 (P3), despite the unchanged NO2 column. It recovered to 2019 level at the end of March (P4). The East China (22°N - 42°N, 102°E - 122°E) received greater influence from COVID-19. Overall NOx emission from East China for 2020 first quarter is 40.5% lower than 2019, and in P4 it is still 22.9% below the same period in 2019. The 40.5% decrease of NOx emission in 2020 first quarter in East China lead to 36.5% increase of surface O3 and 12.5% decrease of surface PM2.5. The elevated O3 promotes the secondary aerosol formation through heterogeneous pathways. We recommend that the complicated interaction between PM2.5 and O3 should be considered in the emission control strategy making process in the future.

[TG-FTIR analysis of thermal degradation of bischofite's crystals with aniline hydrochloride].

The dehydration of bischofite is the key to the use of magnesium resource. Double salts or complex method is an important way to prepare anhydrous magnesium chloride. The crystals of bischofite and aniline hydrochloride were prepared through lowering the temperature of the mixture's aquatic solution slowly. The pyrolysis of aniline hydrochloride, bischofite and the crystals was qualitatively analyzed by TG-FTIR under 400 degrees C. We infered the reaction process through qualitative detection of escaping gas of each decomposition step. The Experimental results showed that there were three steps in the thermal decomposition of bischofite. In the first step, nearly four crystallized waters decomposed, while hydrolysis and decomposition took place together in the next two steps, but hydrolysis was the main reaction at the lower temperature (205-235 degrees C), and comparative decomposition was the main one at the higher temperature (235-287 degrees C). In the experimental temperature range, aniline hydrochloride didn't decompose. Water and aniline hydrochloride left the crystals at different temperature, and no hydrolysis reaction occurred. Anhydrous magnesium chloride can be prepared though this way.