Digital photographic method to quantify black carbon in ambient aerosols

A digital photography based method, Digital Optical Method for Black Carbon (DOM-BC), was developed to quantify the concentration of aerosol black carbon (BC). In this method, a measured volume of ambient air passed through an aerosol sampler, and the aerosol particles were collected onto a quartz fiber filter. Digital pictures of the filter were taken, and then analyzed to determine the optical attenuation (ATN) of the particle layer on the filter. The ATN was related to the mass loading of BC, in μg BC per cm2 of filter area, by performing calibration against thermal–optical analysis (TOA). The average aerosol BC concentration was then calculated with known BC loading, sampling time, and filter area. calibration was carried out using one set of samples collected in Xiamen. The results showed that the BC loading was linearly related to the ATN of the particle layer when the ATN was lower than 150. When the ATN increased beyond 200, an exponential correlation was observed. This method was validated by analyzing the samples collected in Xiamen from 06/2009 to 01/2011. For all the samples taken in Xiamen, the average relative error was <10.7% when comparing with the TOA measurements. DOM-BC was further evaluated by conducting statistical tests. Uncertainty analysis indicated an overall uncertainty of 7% for this method.