Upper-Air Visibility Observations during a Severe Haze Pollution Period Based on Raman–Mie Lidar in Urban Beijing

Along with the rapid development of socio-economic development, industrialization and urbanization in recent year, air pollution is growing worse in urban area across much of the globe, hitting the city dwellers hardest and contributing to a wide range of potentially health problem. The haze pollution is one of an intractable problem among the developing countries, especially for most East Asia region. People in developing countries have limited awareness of the haze problem at present, hence it is necessary to observe and analyze the severe haze process.

In the past two decades, the atmospheric pollution problem in China has increased abruptly.Researchers have carried out a lot of experiments to explain the formation and dissipation of the pollutants, analysis the optical properties of aerosols and understand the haze effects on visibility near the ground.However, less focus was attached to the characteristic of visibility in the upper air.Therefore,we propose the concept of upper air visibility, which is effectively represent the visibility in different altitude of the horizontal direction and expand the parameters that can be detected in the aerosol. The concept of upper air visibility can be widely used in the fields of aerospace and aviation, and it is also an important indicator for weather change.

The research was based on Raman-Mie Lidar system located at Beijing Institute of Technology (BIT-RML). We observed a severe haze weather process around the January 2017 and analyzed the data in detail. Parameters of aerosol optical thickness(AOT), haze thickness (HT),atmospheric boundary layer(ABL) are used to describe the vertical aerosol parameters. We find out the correlation between upper air visibility and various haze parameters observed by Lidar, and make an analysis of the reasons for the decrease in upper air visibility combined with the sounding data.

The conclusions of the study include of the following: (1) The upper air visibility of non-haze days is 3-5 times higher than that on haze days.(2) A statistical analysis of the haze parameters shows that the higher boundary layer or the smaller haze thickness as well as the smaller aerosol optical thickness has positive correlation with the upper air visibility.(3) The intensity and height of inversion layer also have significant effects on the upper air visibility.