Abstract
Long-term visibility (1968–2010) and air pollutant (1984–2010) data records in Hong Kong reveal that the occurrence of reduced visibility (RV, defined as the percentage of hours per month with visibility below 8 km in the absence of rain, fog, mist or relative humidity above 95%) in southeast China has increased significantly in the last four decades. The most pronounced rate of increase was observed after 1990 (nine times higher than that before 1990), when notable increases in surface ozone (O3) levels were simultaneously observed (1.06 µg m−3 per yr). The greatest increases in RV, and in O3, NO2 and SO2 concentrations are coincident in the autumn (1.47, 0.20 and 0.45 µg m−3 per yr respectively), when southeast China is strongly influenced by regional O3 formation and accumulation due to continental outflow of pollution from the east China coast under favourable meteorological conditions. Multiple regression revealed that the RV percentage correlated well (p<0.05) with NO2 and NOx in the 1980s, and with NO2, SO2 and O3 after the 1990s, suggesting that there have been changes in the predominant factors causing visibility degradation. In order to elucidate the reasons for these changes, the results were integrated with data from previous research. Possible impacts of elevated O3 on secondary particle formation and their effects on visibility degradation and aerosol radiative forcing in an oxidant-enhanced southeast China are highlighted. Other factors potentially leading to visibility degradation, such as ship emissions and biomass burning, are also discussed.
Highlights
The severe air pollution manifested by frequent occurrence of hazy days in China and its impact on the ecosystem and regional climate have been a major concern of the general public and a focus of the international scientific community in recent years (e.g., Shao et al, 2006; Rosenfeld et al, 2007; Thach et al, 2010)
We report measurements which show that atmospheric visibility in Hong Kong deteriorated rapidly in the last four decades, especially during the 1990s and beyond
These results are attributed to the influence of rapid development and associated emissions in the highly populated cities in eastern China on atmospheric composition and visibility in downwind southeast China
Summary
The severe air pollution manifested by frequent occurrence of hazy days in China and its impact on the ecosystem and regional climate have been a major concern of the general public and a focus of the international scientific community in recent years (e.g., Shao et al, 2006; Rosenfeld et al, 2007; Thach et al, 2010). Visibility data recorded across China revealed that visibility across the country has been degrading rapidly, especially in the urban and. The visibility record has been found to have a vital implication for public health research owing to the contribution of fine particulates (Huang et al, 2009; Thach et al, 2010), and to regional climate due to aerosol radiative forcing (Rosenfeld et al, 2007). With continuous urban and industrial development in eastern and southern China, including the PRD, it is important to explore the long-term changes in pollutant levels resulting from such development, and their effect on visibility in Hong Kong. We examine 43-yr visibility and 27-yr air quality datasets from Hong Kong in order to characterise their long-term trends and statistical relationships, and to ascertain their implications for atmospheric chemistry in southeast China. The likely dominant chemical mechanisms, leading to formation of secondary particulate matter (especially sulphate) in such an oxidant-rich atmosphere are discussed
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
