Implications of regional surface ozone increases on visibility degradation in southeast China

Abstract

A B S T R A C T Long-term visibility (1968Á2010) and air pollutant (1984Á2010) 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 (O 3 ) levels were simultaneously observed (1.06 mg m (3 per yr). The greatest increases in RV, and in O 3 , NO 2 and SO 2 concentrations are coincident in the autumn (1.47, 0.20 and 0.45 mg m (3 per yr respectively), when southeast China is strongly influenced by regional O 3 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 B0.05) with NO 2 and NO x in the 1980s, and with NO 2 , SO 2 and O 3 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 O 3 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.

Regression Analyses between Recent Air Quality and Visibility Changes in Megacities at Four Haze Regions in China

“…This result also agrees with the fact that SO 2 dissolves more readily in water and oxidizes into secondary sulfates via heterogeneous reactions at low temperatures (Ota and Richmond, 2011). A similar relationship between SO 2 and visibility impairment was also found in Hong Kong, another megacity in the PRD (Lin et al, 2012 decreases in visibility were probably due to the reduction of WS (0.75 m/s in 2005 to 0.53 m/s in 2009), although the coefficient was just 2.01 km per m/s, too low to trigger the notably decreasing trend in visibility. This indicates that visibility degradation in Chengdu was still affected by other unknown factors.…”

Influences of Commuting Mode, Air Conditioning Mode and Meteorological Parameters on Fine Particle (PM2.5) Exposure Levels in Traffic Microenvironments

“…However, such cases were very rare (Fig. 4), and typically only occur when this region was influenced by tropical cyclones (Chan and Chan, 2000;Zhang et al, 2010;Lin et al, 2012). On the other hand, the elevated PM 2.5 concentrations observed in southeasterly wind sectors were likely due to large PM 2.5 emission in its upwind region (i.e., Dongguan, Zhongshan and Shenzhen) (Fig.…”

Resolving the impact of stratosphere‐to‐troposphere transport on the sulfur cycle and surface ozone over the Tibetan Plateau using a cosmogenic 35S tracer

“…However, large uncertainties still remain because of incomplete knowledge of chemical transformation rates and pathways of sulfur dioxide (SO 2 ) to SO 4 2− [ Dupart et al , ; Harris et al , ; He et al , ]. For example, a faster SO 2 oxidation rate was found in east China due to large emissions of O 3 precursors in this region [ Bell et al , ; Unger et al , ; Lu et al , ; Lin et al ., 2012a], where the SO 2 oxidation pathway may be dominated by both aqueous O 3 oxidation and transition metal‐catalyzed O 2 oxidation [ Li et al , ]. Likewise, if levels of O 3 were enhanced from a stratospheric source, one can expect that tropospheric SO 2 oxidation rates and pathways may be also modulated.…”