Aerosol Optical Properties and Instrument Comparisons in October 2019

One of the important parameters reflecting aerosol properties is aerosol optical depth (AOD). The aerosol optical properties and the impact of meteorological conditions on pollution levels were analyzed in a special period in Beijing during October 2019. There were pollution events during this period, whereas the National Day celebration and military parade were held during this period, with traffic restriction and factory emissions reduction measures taken place to improve the air quality. In this study, AOD was calculated from synchronous observation of two sun photometers installed in the experimental base of atmospheric sounding of CMA Meteorological Observation Centre, and the causes of errors of the two instruments under different weather conditions were preliminarily analyzed. The observation results of the two instruments were consistent, and the AOD deviation was basically lower than 0.03 (@AOD=0.2), with the relative deviation smaller than 10%. The main reasons for the difference were summarized as follows: 1) Although the AOD calculation is based on the same principle, the settings of parameters, such as temperature correction coefficient, were different due to different instrument structures. 2) Due to the difference in data interval caused by the observation mode, there were differences in data time matching. Apart from that, the instantaneous AOD changes greatly, the difference between the two instruments increases accordingly. 3) Meteorological conditions, such as obvious dust and rainfall events, affected the accuracy of instrument observation, and short-wave observation is more sensitive to those changes.