Aerosol
Description
Aerosols, solid particles including particulate matter or liquid droplets suspended in the atmosphere, are measured as terms of Aerosol Optical Depth (AOD), Single Scattering Albedo (SSA), and Ultraviolet (UV) and Visible Light Spectrum (VIS) aerosol index. The AOD shows how much sunlights are scattered or absorbed by aerosols in the atmosphere, and becomes higher if more aerosols stay in the atmosphere. The SSA is a ratio of scattering efficiency to total extinction efficiency, which is ranged between 0 and 1. A value of 1 indicates that a larger amount of light was scattered by atmospheric aerosols rather than those absorbed. The UV index and the VIS index are used to infer aerosol absorbing properties and aerosol sizes, respectively. Additionally, these indices can be used to identify the aerosol type such as fine particulate matter, yellow dust, soot, and so on.
Aerosols can adversely affect the human respiratory system and industries such as semiconductors manufactured under the aerosol-free conditions.
Applications
Aerosol products retrieved from GEMS observations can be applied to support air quality forecasts and environmental policies. Furthermore, the retrieved data can be used in estimating particulate matter concentration and air pollution level around the ground.
AOD less than 0.3 indicates clean atmosphere; higher than 0.7 means polluted atmosphere; and higher than 1.0 denotes severe air pollution due to yellow dust, wildfires, etc. AOD values vary depending on atmospheric conditions. Also, there is another important note on interpreting AOD data. Clouds can be mistaken for aerosols over the minimum spatial resolution area (i.e., single pixel) and may have influence on AOD data. SSA needs to be carefully interpreted over areas where aerosols signals are weak due to large uncertainties in retrieving SSA. Therefore, only SSA data from strong signals of aerosols, in which AOD is larger than 0.4, are recommended to use. The final caution in interpreting aerosol data is as follows. Spatial distribution of AOD is not completely the same as those of concentrations for particulate matter (PM10 and PM2.5) because satellite products are retrieved for the whole air column ranged from the ground to the top of the atmosphere while PM10 and PM2.5 are measured near the ground. In addition, additional information on atmospheric condition (wind direction and speed, weather, etc.) should also be taken into account.