Quantifying the impacts of emissions and meteorology on the interannual variations of air pollutants in major Chinese cities from 2015 to 2021

Air pollutant concentration is a function of emission rates and meteorology.To accurately evaluate the effect of control measures,the meteorological covariate must be corrected from the observations.This study quantified the impacts of emission abatement and meteorological condition on the interannual variations of SO_(2),NO_(2),CO,O_(3),PM_(10) and PM_(2.5) concentrations in 31 major Chinese cities using an optimized machine learning-based meteorological normalization technique.Overall,the annual average concentrations of SO_(2),NO_(2),CO,PM_(10)and PM_(2.5)were reduced by 86%,51%,99%,86% and 88%from 2015 to 2020,respectively,in the studied cities,attributable to their emission reductions.However,the concentration of O_(3) was found with no significant decrease with the reduction of precursors.Emission abatement notably improved air quality between 2015 and 2018.Such a decline in emissions tended to progressively slow down since 2018.Overall,the meteorological conditions in 2016–2017 and 2018–2019 were unfavorable for a better air quality,while it became favorable in 2020–2021.Specifically,emission abatement in 2021 further lowered the concentrations of SO_(2),NO_(2),CO,and PM_(2.5),while the emission of PM_(10) increased.And changes in precursors emissions worsened O_(3) air quality.To meet the demand of improving air quality,more aggressive abatement measures need to be formulated to synergistically reduce NOx,volatile organic compounds,and coarse particles.

Silver-catalyzed unstrained C(CO)–alkyl bond scission via[3+2]/retro-[3+2]cycloaddition of ketones with N-isocyanoiminotriphenylphosphorane

C(CO)–alkyl bonds are ubiquitous in a variety of organic molecules,and their selective activation and functionalization are important for the reconstruction of simple ketones into valuable building blocks.However,due to the thermodynamic and kinetic stability,the cleavage and transformation of the unstrained C(CO)–alkyl bonds remain a significant challenge.Herein,we report a novel silver-catalyzed scission of the unstrained C(CO)–alkyl bond of ketones by reacting with N-isocyanoiminotriphenylphosphorane(NIITP)under mild conditions.This method could transform a variety of unstrained ketones into iminophosphoranes and nitriles in high yields.Experimental and computational studies disclosed the reaction proceeded through an unprecedented[3+2]/retro-[3+2]cycloaddition mechanism.