Investigation of Optical Properties of Size-selected Black Carbon Under Controlled Laboratory Conditions PDF Download

Author: Ziying Lei
Publisher:
ISBN:
Category :
Languages : en
Pages : 80

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Book Description
Air pollution, one of the most concerning and widespread environmental issues has grown in importance in the world. The carbonaceous aerosols significantly contribute to air pollution, which not only causes public health concern, but also impacts climate change. The aerosol particles have properties to absorb or scatter solar radiation and thermal radiation; therefore, they play an important role in climate change. In order to improve the understanding and control the aerosol particles, it is crucial to study aerosol size distribution and chemical compounds. Black carbon is the strongest radiative absorber suspends in the atmosphere, and can have great influence on climate change. This study investigates the size-selected black carbon optical properties under laboratory conditions with varied relative humidity referred to “dry”, “humid”, and “wet” respectively. The single scattering albedo that measures the relative amount of aerosol light extinction due to scattering, and the absorption enhancement due to lensing effect are measured in this study, and compared with the modeling results based on Mie theory, which is used to predict the absorption and scattering of light by a spherical particle. The results show that the single scattering albedo under the dry, humid, and wet conditions are similar, while the single scattering albedo for black carbon particles that have undergone heating to 160 oC is slightly greater than other three conditions. In general, with respect to particle size, single scattering albedo increases with smaller particle size and then levels off at larger size diameters. In addition, the absorption enhancement for black carbon particles is estimated in this study, and it ranges from 1 to 2.5. The values based on observations generally follow the predicted trend from Mie theory. Comparing the observed and modeled values suggests that 25%-50% of the total particle diameter is attributable to coating material. Dry black carbon particles do not have high absorption enhancement because they likely have no or thin coating materials. However, the absorption enhancement for humid particles and wet particles are higher than the dry particles, likely due to an enhanced lensing effect due to water uptake by the black carbon particles. Future study will focus on improving the understanding of black carbon optical properties and accuracy of experimental results. Further research is recommended to focus on ranges of BC particles with the diameters smaller than 100 nm and larger than 650 nm, which are not included in this study and constrain the particle charge units.