The environmental impact of industrially important plastics can be minimized by using renewable feedstocks and preparing biodegradable polymers. A significantly more meaningful strategy is the utilization of alternating copolymerization of epoxides and cyclic anhydrides or lactone or CO 2 to provide degradable polyesters or polycarbonates. Herein, we report a versatile and efficient catalyst system based on dinuclear chromium complex bearing biphenol linking bridge for copolymerizing epoxides with cyclic anhydrides or CO 2 or dihydrocoumarin (DHC), affording various degradable copolymers with perfectly alternating structure and narrow molecular weight distribution. Most of the polyesters from DHC are typical semicrystalline materials, being beneficial to the potential application of aliphatic polyesters as structural materials. Notably, this dinuclear chromium catalyst system was also discovered to be very efficient in the one-pot terpolymerization of cyclohexene oxide/phthalic anhydride/CO 2 , cyclohexene oxide/phthalic anhydride/DHC, or cyclohexene oxide/CO 2 /DHC, providing polyester-b-polycarbonate, polyester-b-polyester, or poly(ester-random-carbonate), respectively. This approach is valuable for the preparation of various novel materials with tailored property and functionality.

Photochemical smog, characterized by high concentrations of ozone (O) and fine particles (PM) in the atmosphere, has become one of the top environmental concerns in China. Volatile organic compounds (VOCs), one of the key precursors of O and secondary organic aerosol (SOA) (an important component of PM), have a critical influence on atmospheric chemistry and subsequently affect regional and global climate. Thus, VOCs have been extensively studied in many cities and regions in China, especially in the North China Plain, the Yangtze River Delta and the Pearl River Delta regions where photochemical smog pollution has become increasingly worse over recent decades. This paper reviews the main studies conducted in China on the characteristics and sources of VOCs, their relationship with O and SOA, and their removal technology. This paper also provides an integrated literature review on the formulation and implementation of effective control strategies of VOCs and photochemical smog, as well as suggestions for future directions of VOCs study in China.

Ozone (O3), a main component in photochemical smog, is a secondary pollutant formed through complex photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs).

Reducing the amount of organic aerosol (OA) is crucial to mitigation of particulate pollution in China. We present time and air-origin dependent variations of OA markers and source contributions at a regionally urban background site in South China. The continental air contained primary OA markers indicative of source categories, such as levoglucosan, fatty acids, and oleic acid. Secondary OA (SOA) markers derived from isoprene and monoterpenes also exhibited higher concentrations in continental air, due to more emissions of their precursors from terrestrial ecosystems and facilitation of anthropogenic sulfate for monoterpenes SOA. The marine air and continental–marine mixed air had more abundant hydroxyl dicarboxylic acids (OHDCA), with anthropogenic unsaturated organics as potential precursors. However, OHDCA formation in continental air was likely attributable to both biogenic and anthropogenic precursors. The production efficiency of OHDCA was highest in marine air, related to the presence of sulfur dioxide and/or organic precursors in ship emissions. Regional biomass burning (BB) was identified as the largest contributor of OA in continental air, with contributions fluctuating from 8% to 74%. In contrast, anthropogenic SOA accounted for the highest fraction of OA in marine (37 ± 4%) and mixed air (31 ± 3%), overriding the contributions from BB. This study demonstrates the utility of molecular markers for discerning OA pollution sources in the offshore marine atmosphere, where continental and marine air pollutants interact and atmospheric oxidative capacity may be enhanced.