Could We Achieve the On-Line Measurements of the Optical Fractal Dimensions of Black Carbon?

Abstract

Significant uncertainties exist in quantifying black carbon (BC) warming effects on earth due to the variation in its light absorption abilities, which depend on its morphology. The fractal dimension ((Formula presented.)) of BC aggregates, is a critical morphology factor determining BC's absorption properties. However, (Formula presented.) cannot be measured online, making it hard to study the BC morphology evolution during atmospheric aging processing. We propose a novel method to measure BC's (Formula presented.) by establishing the relationship between BC's mobility diameter ((Formula presented.)), (Formula presented.), and mass concentration ((Formula presented.)). This method enables to measure the (Formula presented.) of BC aggregates online by measuring their (Formula presented.) and (Formula presented.) concurrently with an accuracy of 0.15. Field measurements show that the ambient BC (Formula presented.) ranges between 2.14 and 2.41 at a suburban site in China. This approach provides an efficient means to measure (Formula presented.) online, making it possible to track the ambient BC morphology evolution and constrain the BC optical and radiative properties.