Effects of meteorology and secondary particle formation on visibility during heavy haze events in Beijing, China

摘要: The causes of haze formation in Beijing, China were analyzed based on a comprehensive measurement, including PBL (planetary boundary layer), aerosol composition and concentrations, several important meteorological parameters such as visibility, RH (relative humidity), wind speed/direction. measurement was conducted an urban location from Nov. 16, 2012 to Jan. 15, 2013. During the period, visibility varied > 20 km less than kilometer, with minimum 667 m, causing 16 occurrences. occurrences, speeds 1 m/s, concentrations PM2.5 (particle matter radius 2.5 μm) often exceeded 200 μg/m3. correlation between concentration under different values shows that exponentially decreased increase when 80%. However, higher 80%, relationship no longer follow decreasing trend, maintained very low values, even concentrations. Under this condition, hygroscopic growth particles played roles, large amount water vapor acted particle (PM) for reduction visibility. variations (RH, heights, WS (wind speed)), chemical species gas-phase (CO, O3, SO2, NOx), particle-phase conversions ranges analyzed. results show high (> 20 km) (< 2 km), averaged 1.24 km 0.53 km; reduced 1 m/s 0.5 m/s; CO increased 0.5 ppmv 4.0 ppmv, suggesting weaker transport/diffusion caused This study also found SPM (secondary matter) accelerated events. SO2 SO4 well NOx NO3− increased, especially humidity conditions. When 70%, accounted about 20% PM2.5, indicating secondary had contribution occurrences Beijing.