Study on Aerosol Optical Properties and Cloud Condensation Nuclei Activation Characteristics in Western Yangtze River Delta,China

Author:Shen Yi Cheng

Supervisor:yuan jian ding ai jun


Degree Year:2019





Atmospheric aerosols directly alter the radiation balance by scattering and absorbing incident sunlight,and altering the albedo and life cycle of the cloud by serving as cloud condensation nuclei(CCN)hence indirectly affect the radiation balance.The radiative forcing caused by both direct and indirect effects of aerosols has a profound impact on global climate change and creates greatest uncertainty in global and regional climate assessments.The Yangtze River Delta(YRD)urban agglomeration is a densely populated regions featured with complex emission sources and transmission characteristics.High aerosol loading and large diversity in aerosol physiochemical properties makes this region a hot-spot for climate research.Based on long-term observations and field campaigns at Station for Observing Regional Processes of the Earth System(SORPES),this study discusses aerosol optical properties(AOPs),aerosol hygroscopicity and CCN activation characteristics in the western part of the Yangtze River Delta.Clear relationship between AOPs,Particle size distribution(PSD)and CCN number concentration(NCCN)has also been found,and a novel parameterization use AOPs to estimate CCN is also proposed in this study.Based on long-term measurement of aerosol optical properties.This study reveals that AOPs show clear diurnal and seasonal cycle and influenced by local and regional transportation.Quasi-synoptic scale evolution of aerosol loading and AOPs has also been found.Particular matters usually go through a week-long accumulation processes before scavenging,during which the secondary formation makes the particles larger and brighter along with increasing aerosol loading.The variation of most AOPs in such’pollution episodes’ are clear and the extend of such variation are much larger than diurnal and seasonal variation.As a consequence of such variation,Single scattering albedo(SSA)and backscatter fraction(BSF)negatively correlated with each other which finally result in a relatively stable negative direct radiation forcing.Long term measurement result shows that NCCN peaks at December,and a extensive measurement campaign including CCN activation,hygroscopicity growth and chemical composition was carried out around December 2018.The results show that CCN concertation of the Yangtze River Delta is high while the hygroscopicity is strong.The average values of Κchem and ΚCCN are 0.43 and 0.34,respectively.The variation of hygroscopicity is affected by the proportion of organic matter and the state of oxidation,but exhibits different slope and intercept during four period with different transportation pattern.In general,the aerosol hygroscopic characteristics exhibited by the chemical composition,CCN activation and hygroscopic light-scattering enhancement consistence with each other.However,the correlation coefficient between each other is relatively low because their size dependency is different.By observing the activation spectra under different supersaturation ratios(SS),it is found that the hygroscopic parameter ΚCCN at~50 nm is significantly lower than that of~80 nm and~150 nm,indicating that the organic matter grows in the granules in the western part of the Yangtze River Delta.The initial occupation is relatively large.By studying the relationship between CCN,optical properties and particle size distribution,it is found that aerosol optical parameters in the western part of the Yangtze River Delta can serve as a proxy for aerosol loading and particle size distribution thus can be used for CCN estimation.On this basis,the long-term measurement data from six very different locations worldwide:west Yangtze River Delta,the boreal forest,the US West Coast,the Amazon rainforest,an Atlantic island and the Ganges Valley were carefully analysis and further used for make a general-combined parameterization.The parameterization successfully estimated CCN number concertation use nephelometer measurement only,i.e.scattering coefficient,back scatter fraction and scattering Angstrom exponent.Simulation use Mie scattering theory and the K-Kohler equation can reproduce the key steps in the establishment of the parameterization scheme and explain the mathematical and physical nature behind the parametric scheme to some extent.This study provides an in-depth discussion of the optical properties and hygroscopic parameters of this typical region in the western part of the Yangtze River Delta.It provides strong data support and theoretical support for the study of direct radiative forcing and aerosol-cloud-interaction in this region.The parameterization scheme designed in this study can serve as a supplement for the direct CCN measurement,and has scientific significance and practical application value.