A comparison of haze pollution variability in China using haze indices based on observations

Defining the occurrence and degree of haze pollution (HP) in China has been extremely controversial in recent years. This study elaborates on the meanings of ten most frequently used HP indices based on observation and compares their performance in measuring the HP variability in China concerning the annual cycle, interannual variations and interdecadal trends for the period of 1980-2015. It is found that these indices exhibit a high consistency in South China, while apparent discrepancies exist in North Chinam, Sichuan Basin and the Yangtze River Delta. Observed surface PM_2.5 concentration is utilized to assess the performance of the ten HP indices. Results show that some of these indices can well capture primary features of the HP in some specific area, only these defined by a daily averaged value or 14:00 single threshold value have relatively good performance in the whole Eastern China. Such four indices (HPI2/HPI3/HPI4/HPI5) exhibit high consistence in depicting spatial-temporal variations (from annual cycle to interannual variability) of surface PM_2.5 concentration over China, meaning they can highlight the significance of high aerosol concentration in triggering HP events. Moreover, further analysis suggest that the contributions of weather conditions to the occurrence and degree of the HP is becoming more in China, especially in the NC, SCB, YRD regions. These results provide useful guidance for monitoring variations of the HP in China and for making long-term environmental regulatory and controlling policy.