Abstract
Images based on RGB pixel values were used to measure the extinction coefficient of aerosols suspended in an atmospheric state. The pixel values of the object-image depend on the target-object reflection ratio, reflection direction, object type, distances, illumination intensity, atmospheric particle extinction coefficient, and scattering angle between the sun and the optical axes of the camera, among others. Therefore, the imaged intensity cannot directly provide information on the aerosol concentration or aerosol extinction coefficient. This study proposes simple methods to solve this problem, which yield reasonable extinction coefficients at the three effective RGB wavelengths. Aerosol size information was analogized using the RGB Ångström exponent measured at the three wavelengths for clean, dusty, rainy, Asian dust storm, and foggy days. Additionally, long-term measurements over four months showed reasonable values compared with existing PM2.5 measurements and the proposed method yields useful results.
Highlights
We proposed and discussed a new method for measuring the extinction coefficients of atmospheric particulates using an arbitrary landscape image
The following represent the advantages of this method, (1) extinction coefficients can be obtained regardless of cloud or weather conditions, (2) extinction coefficients can be measured not just at one point, but at an average of points over a wide area, (3) we have no limit in temporal resolution because it depends on the shooting time of the camera, (4) the extinction coefficient can be obtained at three wavelengths at once, the size information of the aerosol can be obtained, (5) most importantly, it provides different physical quantities and units from conventional methods (PM2.5/10 values), (6) the use of the extinction coefficient in conjunction with PM2.5/10 is advantageous to obtain other information about the aerosol
We checked the effects of object distances and direction of the targets on the retrieving extinction coefficients and found that the direction of the sun and camera have no effect on the retrieving results
Summary
Optical methods measure the aerosol cross-section (area) using transmittance or scattering methods, referred to as LiDAR (Light Detection and Ranging), OPC (Optical Particle Counter), visibility system, and nephelometer Most of these point measurement systems measure small volume and require time to obtain a high signal-to-noise ratio (SNR) at the expense of the temporal resolution [3]. All sky images contain scattering information for the particles distributed from the bottom to the top of the atmosphere (TOA); we can retrieve the aerosol optical depth from the bottom to the TOA [19] In this case, we should solve the full radiative transfer equations [20] for a given complex cloud distribution and height, as well as for an assumed aerosol vertical distribution for every minute of the day.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
