Beijing Weather Modification Office, Beijing, China.
SKLLQG and Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xian China; National Center for Atmospheric Research, Boulder, CO, USA.
Sci Total Environ. 2015 Jan 1;502:578-84. doi: 10.1016/j.scitotenv.2014.09.079. Epub 2014 Oct 7.
The causes of haze formation in Beijing, China were analyzed based on a comprehensive measurement, including PBL (planetary boundary layer), aerosol composition and concentrations, and several important meteorological parameters such as visibility, RH (relative humidity), and wind speed/direction. The measurement was conducted in an urban location from Nov. 16, 2012 to Jan. 15, 2013. During the period, the visibility varied from >20 km to less than a kilometer, with a minimum visibility of 667 m, causing 16 haze occurrences. During the haze occurrences, the wind speeds were less than 1m/s, and the concentrations of PM2.5 (particle matter with radius less than 2.5 μm) were often exceeded 200 μg/m(3). The correlation between PM2.5 concentration and visibility under different RH values shows that visibility was exponentially decreased with the increase of PM2.5 concentrations when RH was less than 80%. However, when RH was higher than 80%, the relationship was no longer to follow the exponentially decreasing trend, and the visibility maintained in very low values, even with low PM2.5 concentrations. Under this condition, the hygroscopic growth of particles played important roles, and a large amount of water vapor acted as particle matter (PM) for the reduction of visibility. The variations of meteorological parameters (RH, PBL heights, and WS (wind speed)), chemical species in gas-phase (CO, O3, SO2, and NOx), and gas-phase to particle-phase conversions under different visibility ranges were analyzed. The results show that from high visibility (>20 km) to low visibility (<2 km), the averaged PBL decreased from 1.24 km to 0.53 km; wind speeds reduced from 1m/s to 0.5m/s; and CO increased from 0.5 ppmv to 4.0 ppmv, suggesting that weaker transport/diffusion caused the haze occurrences. This study also found that the formation of SPM (secondary particle matter) was accelerated in the haze events. The conversions between SO2 and SO4 as well as NOx to NO3(-) increased, especially under high humidity conditions. When the averaged RH was 70%, the conversions between SO2 and SO4 accounted for about 20% concentration of PM2.5, indicating that formation of secondary particle matter had important contribution for the haze occurrences in Beijing.
基于综合测量，包括边界层（行星边界层）、气溶胶成分和浓度以及能见度、相对湿度 (RH) 和风速/风向等几个重要气象参数，分析了中国北京雾霾形成的原因。测量于 2012 年 11 月 16 日至 2013 年 1 月 15 日在城市地区进行。在此期间，能见度从>20 公里到不到一公里不等，最小能见度为 667 米，发生了 16 次雾霾事件。在雾霾发生期间，风速小于 1m/s，PM2.5（半径小于 2.5μm 的颗粒物）浓度经常超过 200μg/m³。不同 RH 值下 PM2.5 浓度与能见度的相关性表明，当 RH 小于 80%时，随着 PM2.5 浓度的增加，能见度呈指数下降。然而，当 RH 高于 80%时，这种关系不再遵循指数下降趋势，能见度保持在非常低的值，即使 PM2.5 浓度较低。在这种情况下，颗粒的吸湿增长起着重要作用，大量水蒸气充当颗粒物质 (PM)，导致能见度降低。分析了不同能见度范围内气象参数（RH、边界层高度和 WS（风速））、气相化学物质（CO、O3、SO2 和 NOx）和气相到颗粒相的转化的变化。结果表明，从高能见度（>20 公里）到低能见度（<2 公里），平均边界层从 1.24 公里下降到 0.53 公里；风速从 1m/s 降低到 0.5m/s；CO 从 0.5ppmv 增加到 4.0ppmv，表明较弱的传输/扩散导致了雾霾的发生。本研究还发现，在雾霾事件中，SPM（二次颗粒物）的形成加速了。SO2 和 SO4 之间以及 NOx 到 NO3(-) 的转化增加，尤其是在高湿度条件下。当平均 RH 为 70%时，SO2 和 SO4 之间的转化占 PM2.5 浓度的约 20%，表明二次颗粒物的形成对北京雾霾的发生有重要贡献。
