Determination of aerosol optical depth and particulate matter concentrations using routine web cam measurements

 

Visibility and visual contrast depend on several factors such as aerosol concentration, fog attenuation and humidity as well as gas characteristics. Usually, visibility is determined by observers or by visiometers. Routine web cam photographs of Vienna  have been performed for  2 years from the meteorological measurement platform situated on the roof of one of the buildings of University of Natural resources and Life Sciences overlooking the whole city of Vienna. Photographs are taken every 30 minutes in 6 different azimuthal directions. In the following study, we used routine web cam photographs digitalization to study the correlation between the ratio of some RGB channels as well as intensity fluctuations and the aerosol optical depth and on site particulate matter measurements. We first selected only photographs taken on clear sky days

For ground truth data, we used CIMEL sun photometer data of aerosol optical depth and liquid water content, relative humidity from routine measurements from our measurement platform as well as in situ measurements of particulate matter (PM10) performed by the air quality monitoring network of the city of Vienna.

First, the correlation between the contrast in a horizontal line and the aerosol amounts in the atmosphere and particulate matter concentration as a function of time of the day and azimuthal direction was investigated. We then examined the correlation between the blue to red ratio in a vertical and horizontal line with the aerosol amounts and particulate matter concentration in the atmosphere.

Results obtained showed at some azimuth angles and time of the day correlation coefficient R squared of up to 0.85 between horizontal line contrast and in situ PM 10 and between vertical line blue to red ratio and CIMEL aerosol optical depths measurements.