[Seasonal Variations and Source Apportionment of Carbonaceous Components in Luoyang: Implication for Brown Carbon Contribution].

A total of 98 samples were collected to analyze the seasonal variation and source apportionment of carbonaceous components, especially brown carbon (BrC), of PM2.5in Luoyang during 2018-2019. The concentrations of organic carbon (OC) and elemental carbon (EC) ranged from (7.04±1.82) µg·m-3to(23.81±8.68) µg·m-3and (2.96±1.4) µg·m-3to (13.41±7.91) µg·m-3, respectively, showing the seasonal variation of being high in winter and low in summer; the carbonaceous fraction and secondary organic aerosol percentages were higher by 8.33%-141.03% and by 0.77%-63.14%, respectively, compared with that in 2015. The light absorption cross section (MAC) values showed different seasonal variations with the concentration of carbonaceous fraction, shown in descending order as autumn (7.67 m2·g-1)>winter (5.65 m2·g-1)>spring (5.13 m2·g-1)>summer (3.84 m2·g-1). The MAC values ranged from 3.84 to 7.67 m2·g-1 at 445 nm, which was lower than that in coal ash. Seasonal variation in light absorption and the contribution of BrC to total light absorption (babs,BrC,405 nm, babs,BrC,405 nm/babs,405 nm) in descending order was winter (31.57 Mm-1, 33%), autumn (11.40 Mm-1, 25%), spring (4.88 Mm-1, 23%), and summer (2.12 Mm-1, 21%). The proportion of carbonaceous components decreased as haze episodes evolved, whereas the contribution of light absorption of BrC increased, highlighting the important contribution of BrC to the total light absorption. The results of PMF and correlation coefficients of babs,BrC,405 nm and PM2.5 components indicated that motor vehicles and secondary nitrate contributed 27.7% and 24.0%, respectively. Our findings have significant scientific implications for the deep controlling of carbonaceous aerosol, especially for BrC, in Luoyang in the future.

Tunable stereoselective alkene synthesis by treatment of activated imines with nonstabilized phosphonium ylides.

A broad range of readily accessible N-sulfonyl imines undergo olefination reaction with nonstabilized phosphonium ylides under mild conditions to afford an array of both Z- and E-isomers of 1,2-disubstituted alkenes, allylic alcohols, and allylic amines in good yields and with greater than 99 : 1 stereoselectivity.

Controllable stereoselective synthesis of trisubstituted alkenes by a catalytic three-component reaction of terminal alkynes, benzylic alcohols, and simple arenes.

The acid-catalyzed three-component reaction of terminal alkynes, benzylic alcohols, and simple arenes provides convenient and atom-economic access to an array of both Z- and E-isomers of trisubstituted alkenes with excellent stereoselectivity by switching reaction temperature and acidic catalysts.