Influence of Urbanization on Haze
Defense Meteorological Satellite-Operational Linescan System night-time emission data was applied as a proxy approach to assess urbanization level. Using this approach, it was found the spatial distribution of annual haze days was consistent with that of night-time light intensity in Zhejiang. The intensities of haze and night-time light in Northeastern Zhejiang were greater than those in Southwestern Zhejiang, and the same intensities were higher in coastal areas (than inland areas). The distributions of haze and night-time light both presented the features of regional clusters and boundary crossing between urban and rural areas. From 1960 to 2010, the annual haze days exhibited three change phases separated by two change jumps around 1979 and 2000. The first and second change jumps corresponded to the reform and opening-up and to the intensified urbanization, respectively. A close relationship between haze and total night-time light was found, and the correlation coefficients were higher than 0.9. In the long term, a negative correlation between relative humidity and visibility was observed, but the synchronous delaying trends of relative humidity and visibility reveal that the visibility delay was induced by increased pollutants. A comparison of the change trends of relative humidity, particle concentration, and visibility in Hangzhou and Linan indicates that an atmosphere with drier and heavier air pollution surrounds urban areas. Therefore, urbanization has a significant impact on haze.