Haze formation is closely related t

Haze formation is closely related to meteorological conditions and air pollution. Urban haze generally results from high levels of air particles emitted by anthropogenic sources and gas–to–particle conversion (Tan et al., 2009). Haze is defined as the weather phenomenon which leads to atmospheric visibility less than 10 km due to the suspended solid or liquid particles, smoke, and vapors in the atmosphere. Haze events are characterized by low visibility, low wind speed, high relative humidity, and high levels of SO2 and NOx (Tan et al., 2009). The exact dates on which haze weather happened were obtained from Shanghai Environmental Monitoring Center (SEMC).