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Over the past decade, China has experienced a rapid increase in urbanization. The urban built-up areas
(population) of Shanghai increased by 16.1% (22.9%) from 2006 to 2015. This study aims to analyze
the variations of tropospheric NO2 over Yangtze River Delta region and the impacts of rapid
urbanization during 2006-2015. The results indicate that tropospheric NO2 vertical column density
(VCD) of all cities in the study area showed an increasing trend during 2006-2011 whereas a
decreasing trend during 2011-2015. Most cities showed a lower tropospheric NO2 VCD value in 2015
compared to that in 2006, except for Changzhou and Nantong. Shanghai and Ningbo are two hotspots
where the tropospheric NO2 VCD decreased most significantly, at a rate of 22% and 19%, respectively.
This effect could be ascribed to the implementation of harsh emission control policies therein. Similar
seasonal variability was observed over all cities, with larger values observed in the summer and smaller
values shown in the winter. Further investigations show that the observed increasing trend of
tropospheric NO2 during 2006-2011 could be largely explained by rapid urbanization linked to car
ownership, GDP, power consumption, population and total industrial output. Such effect was not
prominent after 2011, mainly due to the implementation of emission control strategies.
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