Abstract. Extensive fossil fuel combustion in rapidly-developing cities severely affects air quality and public health. We report observational evidence of decadal changes in the efficiency and cleanness of bulk combustion over large cities in mainland China. We combine air quality retrievals from mature satellite instruments across 2005–2014 to estimate the trends in enhancement ratios of CO and SO2 to NO2 (ΔCO / ΔNO2 and ΔSO2 / ΔNO2) over these cities and infer emergent bulk combustion properties. Our results show a robust coherent progression of declining-to-growing ΔCO / ΔNO2 (−5.4 ± 0.7 % to +8.3 ± 3.1 %) and slowly-declining ΔSO2 / ΔNO2 (−6.0 ± 1.0 % to −3.4 ± 1.0 %) from Shenyang, Beijing, Shanghai, to Shenzhen relative to 2005, which is not evident in the trends of emission ratios reported in Representative Concentration Pathway (RCP8.5) inventory. This progression is likely due to a shift towards cleaner combustion from industrial and residential sectors in Shanghai and Shenzhen, which is presently obfuscated by China's still relatively higher dependence on coal. Such progression is well-correlated with economic development and traces a common emission pathway that resembles evolution of air pollution in more developed cities. Our results highlight the utility of augmenting observing and modeling capabilities by exploiting enhancement ratios in constraining the time variation of emission ratios in current inventories. The ability to monitor combustion efficiency and effectiveness of pollution control becomes increasingly important in assessing sustainable control strategies as cities and/or countries continue to socioeconomically develop.
Supplementary material to "Satellite Data Reveals a Common Combustion Emission Pathway for Major Cities in China"
