Quantification of Airborne Elemental Carbon by Digital Imaging

Black carbon emitted from vehicles or industrial plants is a very common phenomenon observed by high school students. A cost effective and user friendly measurement protocol will greatly enhance school students' capability to investigate the black carbon pollutant in their ambient environments, and hence their awareness to environmental protection. This study shows the potential of applying digital imaging as an alternative method to measure airborne elemental carbon (EC). Aerosols were collected on filters and the blackness of the filters was digitalized into RGB values using an office scanner. It was found that maximum value of transformed R, G and B values (255 - R, 255 - G and 255 - B, respectively), max {R',G',B'}, was power-law related with the EC loading of the filter (R-2 = 0.85, n = 55). The power-law relationship between the max{R',G',B'} and EC loading could be applied as a cost effective and user friendly method to quantify EC by high school students. Using this method, the sampling flowrate and duration should be controlled so that the max{R',G',B'} of the filter samples lie in the optimal range between 40 and 170 to minimize the uncertainty. For samples within this range, the average percentage difference between the results of this method and the results from conventional thermal-optical method was found to be only 10.3%, which is close to common research grade instruments.