Comment on amt-2022-137

Abstract

Black carbon (BC) is an important atmospheric component with strong light absorption. Many attempts have been made to measure BC mass size distribution (BCMSD) for its significant impact on climate and public health. Larger-coverage BCMSD, ranging from upper submicron to larger than 1 μm, contributes to substantial proportion of BC absorption. However, current time resolution of larger-coverage BCMSD measurement was limited to 1 day, which was insufficient to characterize variation of larger-coverage BCMSD. In this study, a new method to determine BCMSD was proposed from size-resolved absorption coefficient measured by an aerodynamic aerosol classifier in tandem with an aethalometer. The proposed method could measure larger-coverage BCMSD with time resolution as high as 1 hour and was validated by comparing the measurement results with that measured by a differential mobility analyzer in tandem with a single particle soot photometer (DMA – SP2) for particle size larger than 300 nm during a field measurement in Yangtze River Delta. Bulk BC mass concentration (mBC,bulk) by DMA – SP2 was underestimated by 33 % compared to that by this method because of the limited size range of measurement for DMA – SP2. Uncertainty analysis of this method was performed with respect to mass absorption cross-section (MAC), transfer function inversion, number fraction of BC-containing particle and instrumental noise. The results indicated that MAC was the main uncertainty source, leading to mBC,bulk varied from – 20 % to 28 %. With the advanatage of wide size coverage up to 1.5 μm, high time resolution, easy operation and low cost, this method is expected to have wide applications in field measurement for better estimating radiative properties and climate effects of BC.