Abstract
This study analyzed the long-term variations and trends of haze pollution and its relationships with emission and meteorological factors using the haze days (HDs) data derived from surface observation stations in Sichuan-Chongqing (SCC) region during 1980–2016. The results showed that the multi-year mean number of HDs were 68.7 and 4.9 days for the Sichuan-Basin (SCB) and the rest of SCC region, respectively. The seasonally averaged HDs over SCB reached its maximum in winter (34.7 days), followed by autumn (17.0 days) and spring (11.6 days), and with the minimum observed in summer (5.5 days). The inter-annual variations of HDs in 18 main cities revealed that Zigong, Neijiang, and Yibin, which are located in the southern of SCB, have been the most polluted areas over the SCC region in the past decades. A notable increasing trend in annual HDs over the majority of SCC region was found during 1980–1995, then the trend sharply reversed during 1996–2005, while it increased, fluctuating at some cities after 2006. Seasonally, the increased trend in spring and autumn seems to be the strongest during 1980–1995, whereas the decreased trend in spring and winter was stronger than other seasons during 1996–2005. In addition, a remarkable increasing trend was found in winter since 2006. Using correlation analysis between HDs and emission and meteorological factors during different periods, we found that the variability of local precipitation days (PDs), planetary boundary layer height (PBLH), near-surface wind speed (WS), and relatively humidity (RH) play different roles in influencing the haze pollution change during different historical periods. The joint effect of sharp increase of anthropogenic emissions, reduced PDs and WS intensified the haze pollution in SCB during 1980–1995. In contrast, decreased HDs during 1996–2005 are mainly attributable to the reduction of PM2.5 emission and the increase of PDs (especially in winter). In addition, the decrease of PDs is likely to be responsible for the unexpected increase in winter HDs over SCB in the last decade.
Highlights
In recent decades, as a result of a remarkable increase in the emissions of primary pollutants caused by the rapid development of China’s economy and urbanization, China has frequently suffered from persistent and severe haze events with high concentration of pollutants, which has aroused considerable concern of the society [1,2,3,4,5]
The haze days (HDs) are characterized by atmospheric horizontal visibility less than 10 km and surface relative humidity less than 90%, which removed the influence of the fog [2,14]
We found that the winter mean planetary boundary layer height (PBLH) has a negative correlation with HDs (R = −0.23) during 2006–2016 in SCB
Summary
As a result of a remarkable increase in the emissions of primary pollutants caused by the rapid development of China’s economy and urbanization, China has frequently suffered from persistent and severe haze events with high concentration of pollutants, which has aroused considerable concern of the society [1,2,3,4,5]. Numerous studies have shown that, as a result of the intensification of air pollution (especially fine particulate matter pollution), some potential health risks have been induced, including respiratory. Based on the latest report of the state of Global Air 2018 [13], the deaths attributed to ambient fine particulate matter pollution have exceeded 1.1 million in China. The observed HDs have shown an increasing trend over eastern
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