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A decrease in population is an emerging challenge in China's urbanization trajectory. This study utilizes data from the Sixth and Seventh Population Censuses to identify Chinese cities experiencing population decline, focusing on prefecture-level cities. It employs 30 indicators relevant to nine Sustainable Development Goals (SDGs) concerning urban areas and populations to evaluate the progress of these shrinking cities in 2010 and 2020. A novel metric, "SDG population elasticity", is introduced to quantify the association between population reduction and SDG indexes. The study employs K-means++ clustering for 130 shrinking cities. The findings reveal that out of the 130 cities, 63 exhibit a downward trend in SDG index scores, predominantly in China's northeast and western regions. The Northeast region has negative SDG population elasticity, indicating a lag in sustainable development compared to that in other areas. Additionally, the research categorizes China's shrinking cities into four groups: cities with strong population elasticity feedback-significantly declining SDGs, cities with weak population elasticity feedback-slightly regressing SDGs, cities with high population loss-negative SDGs in decline, and cities with smart population decline-steady SDGs growth. These findings offer a foundation for crafting bespoke policies in shrinking cities to ensure a balanced approach to sustainable development and monitor advancement toward achieving the SDGs. [ABSTRACT FROM AUTHOR]

Molecular analyses help to better understand the overall picture of characteristics, meteorological effects, sources, and secondary transformations of organic aerosols (OA). A two-year observation campaign was conducted in polluted central China during 2019–2021, and 130 compounds of molecular OA (quantified organic compounds, QOCs) were quantified. The average concentration of QOCs was 1971 ng/m3, showing the highest normalized QOCs in PM 2.5 (31 ng/μg) compared to others. Among the QOCs, the polar category contributed 84%, with the dominated abundant fatty acids observed. The enhanced acid ratios of malonic/succinic and octadecanoic/oleic in summer indicated higher aerosol age, significantly promoted by temperature. Three benzenetricarboxylic acids, mostly from secondary formation, also exhibited quite high concentrations in summer. The noticeable presence of carcinogenic polycyclic aromatic hydrocarbons (PAHs) (45% of ∑28PAHs) highlighted severe health risks associated with human exposure, particularly in winter (56 ng/m3, approximately 7 times that in summer). According to the random forest model assessments, meteorological conditions in summer were most conducive to eliminating pollutants, while that in winter contributed 19% of QOC concentration. The Positive Matrix Factorization analysis revealed that anthropogenic secondary organic aerosols (ASOA) and biogenic SOA (BSOA) jointly accounted for 32% of QOCs, followed by biomass burning (20%), coal combustion (17%), vehicle emissions (16%), and cooking (15%). ASOA was positively correlated with O 3 (r = 0.58) and aerosol acidity facilitated ASOA production at 40% < relative humidity <80%. On polluted days, BSOA increased as NO 2 and PM 2.5 increased, contributing to worsened aerosol pollution. In spring and summer, gas-phase oxidation contributed more saturated dicarboxylic acids (52 and 55%), while aqueous-phase conversion predominated in autumn and winter (59 and 66%). This study provides new information on particulate molecular organic compounds as well as the secondary transformation, which is of great significance for formulating the prevention and control measures of aerosol pollution. [Display omitted] • A total of 130 compounds were measured, covering 8 types of polar and 5 types of non-polar molecules. • Winter meteorological conditions were estimated to contribute 19% to organic components. • Anthropogenic SOA was significantly promoted by aerosol acidity (40% < RH < 80%) and O 3. • Aqueous-phase oxidation predominated in the formation of saturated dicarboxylic acids (55%). [ABSTRACT FROM AUTHOR]