Satellite data reveal a common combustion emission pathway for major cities in China

Abstract

Abstract. Extensive fossil fuel combustion in rapidly developing cities severely\naffects air quality and public health. We report observational evidence of\ndecadal changes in the efficiency and cleanness of bulk combustion over\nlarge cities in mainland China. In order to estimate the trends in\nenhancement ratios of CO and SO2 to NO2 ( ΔCO∕ΔNO2 and ΔSO2∕ΔNO2 ) and infer emergent bulk\ncombustion properties over these cities, we combine air quality retrievals\nfrom widely used satellite instruments across 2005–2014. We present results\nfor four Chinese cities (Shenyang, Beijing, Shanghai, and Shenzhen)\nrepresenting four levels of urban development. Our results show a robust\ncoherent progression of declining to growing ΔCO∕ΔNO2 \nrelative to 2005 ( - 5.4 ± 0.7 to + 8.3 ± 3.1 % \u2009yr −1 ) and\nslowly declining ΔSO2∕ΔNO2 ( - 6.0 ± 1.0 to - 3.4 ± 1.0 \u2009%\u2009yr −1 ) across the four\ncities. The coherent progression we find is not evident in the trends of\nemission ratios reported in Representative Concentration Pathway (RCP8.5)\ninventory. This progression is likely due to a shift towards cleaner\ncombustion from industrial and residential sectors in Shanghai and Shenzhen\nthat is not yet seen in Shenyang and Beijing. This overall trend is presently\nobfuscated by China s still relatively higher dependence on coal. Such\nprogression is well-correlated with economic development and traces a common\nemission pathway that resembles evolution of air pollution in more developed\ncities. Our results highlight the utility of augmenting observing and\nmodeling capabilities by exploiting enhancement ratios in constraining the\ntime variation in emission ratios in current inventories. As cities and/or\ncountries continue to socioeconomically develop, the ability to monitor\ncombustion efficiency and effectiveness of pollution control becomes\nincreasingly important in assessing sustainable control strategies.