利用Cloud-Aerosol LiDAR with Orthogonal Polarization (CALIOP)正交极化云—气溶胶激光雷达资料、Aerosol Robotic Network (AERONET)气溶胶观测资料、地面常规气象观测资料和Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT)模式分析了2013年1月份华北地区的3次中重度灰霾天气过程,着重对灰霾天气过程中大气气溶胶的衰减后向散射系数、退偏比和色比等光学参数的垂直分布进行了研究。结果表明,2013年1月份华北地区灰霾天气发生时,低层大气(2 km)以下污染最严重,存在大量的气溶胶粒子。1月29日重度灰霾时气溶胶的后向散射系数增大至0.0045 km^-1·sr^-1,退偏比大于20%,0—8 km高度范围内的色比值大于100%的比例约为36.3%;气溶胶光学厚度从0.2增大至2.1,Angstrom指数由1.4降至0.9,表明气溶胶光学厚度增加的同时,大气中混合的粗粒子气溶胶比重增加。HYSPLIT后向轨迹模拟结果显示:500 m、1000 m和1500 m 3个高度的气流均途经蒙古国、中国内蒙古自治区、西北地区,最后影响华北地区,表明这次灰霾污染事件除受本地排放的气溶胶粒子影响,还受到源于蒙古国、内蒙古、中国西北部地区远程输送的沙尘影响。

Rapid economic development along with urbanization and industrialization has exacerbated air pollution in China, particularly haze pollution, in recent years. The Beijing-Tianjin-Hebei area, the Yangtze River Delta, and the Pearl River Delta region are the three major focus areas of haze pollution in China.
In January 2013, a high-intensity continuous atmospheric haze pollution swept across East Central China. According to the Air Quality Index, this phenomenon occurred five times in Beijing, and the score reached beyond 200 (severe pollution), occurring on January 6—8, 9—15, 17—19, 22—23, and 25—31. At present, studies on haze pollution focus on physical and optical properties, influencing factors, haze source apportionment, aerosol chemistry and other aspects. Few studies investigated the vertical properties of large-scale, high-intensity haze aerosols. Vertical distribution of aerosols is one of the most critical and uncertain factors of radiative forcing and climate impact.
The vertical distribution of aerosol optical properties during haze days in North China Plain (NCP) in January 2013 are analyzed by using Cloud-Aerosol LiDAR with Orthogonal Polarization (CALIOP) data, Aerosol Robotic Network (AERONET) data, ground meteorological observation data, and Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model.
CALIOP laser radar provided the vertical distribution of aerosol and cloud features with high vertical resolution (30 m). The Level1B aerosol layer products of CALIOP that overpass NCP (34°N to 41°N, 114°E to 120°E) in January 2013, including attenuated backscatter coefficient, volume depolarization ratio, and total attenuated color ratio, were used in the study. The AERONET Aerosol Optical Thickness (AOT) at 500 nm and Angstrom exponent of 440—870 nm at the Beijing (39.97°N, 116.38°E) and Xianghe (39.75°N, 116.96°E) sites were used to investigate the aerosol properties in hazy days. In addition, HYSPLIT model was used to simulate the backward trajectory of heavy haze process of NCP (34°N to 41°N, 114°E to 120°E) on January 29, 2013.
Our results are listed as below:
(1) The meteorological elements of three haze events (January 9—15, 22—23, and 25—31) in January 2013 were compared with the 30-year (1980—2010) mean of meteorological elements at the Beijing site. The results showed that the average relative humidity during the haze events is about 47% higher than the 30-year mean and that the average wind speed during the haze events is about 35% lower than the 30-year mean. These findings indicate that the increased relative humidity and decreased wind speed in January 2013 are unfavorable for cleaning aerosols, thereby resulting in severe haze.
(2) The lowest troposphere (<2 km) was polluted most severely during the hazy days in NCP in January 2013. The total attenuated backscatter coefficient increased to 0.0045 km^-1sr^-1, volume depolarization ratios were greater than 20%, and the maximum value of color ratio was greater than 0.8. These findings suggest that aerosol particles aggregate in the lowest troposphere, and a large number of irregular coarse particles coexist during the haze events in NCP.
(3) The color ratios below 2 km and 6—8 km heights increased during the severe haze on January 29. This finding indicates an increased proportion of large particles. The 6—8 km height may be affected by coarse particle aerosol delivery and cloud particles. The lower atmosphere below 2 km is influenced by local construction dust, which resulted in increased proportion of coarse particles.
(4) AOT (500 nm) increased from 0.2 to 2.1, and the Angstrom index decreased from 1.4 to 0.9 during the severe haze on January 29, which indicated that the proportion of coarse particles mixed in the atmospheric aerosol increased. The simulation results of HYSPLIT backward trajectory showed that the airflow at heights of 500 m, 1000 m, and 1500 m comes from Mongolia, Inner Mongolia, China, and Northwest China, and finally affects the NCP.
Three severe haze events in NCP in January 2013 were analyzed by using CALIOP data, AERONET data, ground meteorological observation data, and HYSPLIT model. The three-dimensional structure of the haze is provided when the size distribution and possible sources of atmospheric aerosol during haze events are analyzed in depth. Results show that heavy haze pollution in NCP is not only composed of fine aerosol particles from human activities but also accompanied by coarse dust aerosols. Dust aerosols from remote region could affect the haze composition in NCP.