| In recent years,the frequent occurrence of forest fires at home and abroad has not only caused heavy losses to human property,health,and safety.When the forest fire occurs,a large number of smoke particles are also emitted into the atmosphere,which seriously affects air quality,as well as the regional and global climate.Black carbon(BC)particles are an important component of the particulate matter emitted by forest fires,and the accurate calculation of their radiative properties is of great significance for the remote sensing monitoring of fire emitted particles and the climate prediction in the fire region.The morphologies of BC in the forest fire area are extremely complex,while current climate models and remote sensing technologies assume a spherical mor-phology for the BC particles,which causes huge errors in the calculation of BC radiative properties.Besides,other materials(eg.organic carbon)can coat on the surface of BC,and the BC radiative properties turn more complex.In this paper,as the BC in the forest fire exhibits complex morphologies and mixing states,we have studied systematically the morphology and radiative properties of BC particles emitted by forest fires.The main research work is as follows:(1)The three-dimensional morphologies of BC were reconstructed,and the ef-fects of coating structures on the fractal characteristics of coated BC were revealed.It was found that the fractal law is just applicable for the uniformly coated BC.As BC is unevenly coated with organic carbon,the equivalent fractal dimension increases,and the ideal fractal law is inapplicable.The Q space theory was applied to verify the findings,and the difference between the two-dimensional image analysis and the three-dimensional analysis method was analyzed.It was found that the fractal dimen-sion measured by the two-dimensional image analysis method was close to the fractal dimension of bare BC particles.(2)By establishing an acentric core-shell monomer model,the effects of the way how the monomers are coated on the BC radiative properties were studied,and it was found that the way how the monomers are coated has a negligible impact on the radia-tive properties of BC.Morphologically realistic models with adjustable parameters were proposed,and it was revealed that the morphologically realistic models can provide rea-sonable explanations for the observed values of the large backscattering depolarization ratio in the forest fire scene that cannot be explained properly by the current model.We also found that the proposed models show better performance than the simplified model in reproducing experimental measurements.Due to the various morphologies of BC in the atmosphere,it is difficult to represent all the BC morphologies in the at-mosphere using a specific model.Limited adjustable parameters are used to represent various coating structures,which is beneficial to the parameterization of BC radiative properties.(3)Based on the developed non-spherical BC radiative models,a method for eval-uating the influence of the complex BC morphology on the estimation of brown carbon(BrC)absorption was proposed.Based on the non-spherical BC radiative models,the total absorption of mixed BC and BrC was calculated,and it is taken as the pseudo measurements.The commonly used absorption Angstrom exponent(AAE)methods were used to estimate the BrC absorption,the estimated BrC absorption was compared with"True" BrC absorption.The influence of BC morphology on the applicability of commonly used AAE methods is evaluated,and guidance was provided for the use of different AAE methods.(4)The non-spherical BC radiative models were used to investigate the effects of the brown coatings on the absorption enhancement of black carbon,and the applica-bility of the core-shell sphere model under different conditions was evaluated.It was found that the total absorption of externally mixed BrC and BC can be greater than that internally mixed BrC and BC,which is different from the findings previous studies.By instigating the physical mechanism behind this phenomenon,it was found that the outer layer of absorbing BrC coatings would block sunlight from entering the inner BC,and just like a layer of sunglasses,it was named"sunglass effect" in this paper.Besides,this paper has given a clear mathematical definition for the and"sunglasses effect",and has studied the influence of the BC morphology,particle size distribution,and mixing states on the BC"lensing effect" and"sunglasses effect".It was found that the lensing effect changes relatively little with the wavelength,but the sunglasses effect decreases obviously with the increase of the wavelength.(5)The machine learning method was applied to fit the relationship between the complex BC morphology and the radiative properties,and it was verified by the multiple sphere T-matrix results.The machine learning can reconstruct the radiative properties of the entire morphological parameter range through a small amount of training data,and can greatly reduce the computational costs when constructing a large database for the radiative properties of non-spherical BC.(6)By establishing a look-up table for the radiative properties of non-spherical BC,the optical post-processing software,FlexAOD,was improved,so that it can be applied to the calculate the radiative properties of non-spherical BC.Besides,the non-spherical BC radiative models,atmospheric transport model,and the radiative transfer model off-line coupled to investigate the effects of the complex BC morphology on the radiative effect of BC in the forest fire area,which builds the foundation for the application of the non-spherical BC radiative models in large-scale atmospheric models and remote sensing. |
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