Development Of An Aerosol Optical And Hygroscopic Properties Measurement System And Its Application

Atmospheric aerosol has a profound impact on atmospheric environment and climate change,and its the optical and hygroscopic properties are crucial input parameters for calculating atmospheric visibility and aerosol radiative forcing.Black carbon(BC)is the most dominant light-absorbing component of atmospheric aerosols,and the complexity and diversity of the atmospheric aging processes make assessing BC optical and hygroscopic properties more elusive.Therefore,accurate measurement of the aerosol optical and hygroscopic properties is of great significance to reduce the uncertainty in evaluating their environmental and climate effects.However,the existing methods can only characterize a single optical parameter,which limit the exhaustive measurement of the multi-parameter optical hygroscopicity.The application scenarios of developed multi-parameter optical measurement system are fairly single.It is thus difficult to meet the demand for comprehensive and accurate acquisition of aerosol optical and hygroscopic properties,which restricts the in-depth development of related research.In this thesis,a series of detection instruments for measuring aerosol optical and hygroscopic properties in different application scenarios were developed,which had realized in situ measurements of multi-parameter optical and hygroscopic properties,simultaneously.Based on these instruments,the comprehensive optical hygroscopicity of BC was investigated,preliminarily.In addition,a new spectroscopy detection technique had been developed to explore the new generation instruments for measuring aerosol optical and hygroscopic properties.The main contents and innovations of this thesis are as follows:1.A cage type cavity-enhanced albedometer was developed for measuring aerosol optical properties.The new albedometer with a novel optical cage cavity integrated the advantages of high integration and high performance.The detection sensitivities of extinction scattering and absorption coefficients were better than 0.07,0.04 and 0.08 Mm-1,respectively.Laboratory-generated ammonium sulfate particles were used for the demonstration of the accuracy of extinction and scattering coefficients,and the evaluated error of single scattering albedo was less than 2%.The good performances in the Second Tibetan Plateau Scientific Expedition indicated that the instrument can be used for the detection of aerosol optical properties at high altitude background sites.2.A UAV-based cavity-enhanced albedometer and the first comprehensive unmanned airborne observation platform in China were developed for measuring aerosol vertical profiles,which can carry a load of 40 kg and has a battery life of～1 hour.It provides a powerful tool to study the interaction of aerosol-radiation-boundary layer and reveal the causes of heavy pollution.Compared with the ground version,the UAV-based instrument with smaller size and weight,and faster time response,had achieved good performances that the detection sensitivities of extinction,scattering and absorption coefficients were 0.38,0.21 and 0.43 Mm-1 at 1 s acquisition time,respectively,and the error of single scattering albedo was～2%.The measurement of laboratory-generated particles and comprehensive comparison of atmospheric aerosols verified the accuracy of the UAV-based instrument,and the vibration and oil fume of UAV had no effect on the measurement of optical parameters.The application of vertical observation showed that the instrument can also realize the measurement of the vertical profile of aerosol optical properties.3.A optical multi-parameter hygroscopic growth measurement instrument was developed for simultaneous in situ measurements of aerosol extinction,scattering,absorption and single scattering albedo hygroscopicity for the first time.The time resolution of a full RH cycle was 15-20 min,and the uncertainties of extinction and scattering hygroscopic growth factors were 7-25%.Laboratory-generated particles and atmospheric aerosols measurements demonstrated that the instrument can accurately measure aerosol optical hygroscopicity and can be applied to investigate atmospheric aerosols,and the absorption and single scattering albedo hygroscopic growth curves of atmospheric aerosols have been obtained for the first time.In addition,the instrument also realized the first measurement of aerosol optical hygroscopicity in the Tibetan Plateau.4.The optical hygroscopicity of BC was comprehensively studied.Preliminary model calculation showed that the scattering hygroscopic growth of BC-containing particles mainly depended on the hygroscopicity of mixing materials,and the hygroscopic growth of absorption was affected by the hygroscopicity and coating thickness of mixing materials,at the same time.Preliminary laboratory measurement of the directly generated BC showed that BC can undergo slight hygroscopic growth of extinction and scattering,decreasing with the increase of particle diameter.However,the absorption hygroscopicity was not obvious.Guangzhou field observation showed that organic matter and BC can inhibit the hygroscopic growth of scattering,while inorganic salts,especially nitrates,can enhance the scattering hygroscopicity.Based on the developed instrument,a positive correlation between the atmospheric aging degree and absorption hygroscopicity was directly observed for the first time.And the thick coating of organic substances can significantly promote the absorption hygroscopic growth.5.A new instrument for measuring extinction coefficient was developed,which can provide significant technical support for the future development of miniaturized multi-parameter optical and hygroscopic detection instruments.We applied amplitude modulation technique to a multimode diode laser for the first time,and developed an Amplitude Modulated multimode-diode-laser-based Cavity Enhanced Absorption Spectroscopy(AM-CEAS)system for extremely sensitive extinction coefficient detection,achieving 0.05 Mm-1 detection sensitivity at 1 s acquisition time.The accuracy of the new method was proven by the measurements of pure scattering and absorption gases.This AM-CEAS provides a novel method for achieving simultaneous detection at multiple wavelengths using only one cavity and one detector.And further combined with integrating spheres,it also has good application prospects in the measurements of multi-parameter optical and hygroscopic properties.