New methods for characterizing the anthropogenic aerosol mixing state and cloud forming potential

Atmospheric aerosols are complex combinations of different chemical species, and they have an important impact on the climate system by scattering and absorbing solar radiation and interacting with clouds. Atmospheric aerosols also negatively affect air quality and thus human health and ecosystems. With the rapid development of the world economy and urbanization, emissions of anthropogenic aerosols has increased significantly. Thus, it is important to characterise the physicochemical properties of aerosols. However, detailed characterisation of aerosol mixing state and its impact is challenging due to both the instrument limitations and the complicated emission and aging mechanisms. This thesis addresses this issue through three in-situ measurements: two ground-based measurement campaigns and one aircraft measurement campaign. The two ground measurements were conducted in Beijing and its suburban region to investigate the aerosol mixing state in a polluted environment, and the first ground measurement contributes to the Air Pollution and Human Health (APHH) Beijing project. Two novel size classifiers, a Centrifugal Particle Mass Analyzer (CPMA) and an Aerodynamic Aerosol Classifier (AAC), were provided the size-resolved measurements in these two studies respectively. A number of different measurement techniques were placed downstream of the aerosol classifier to measure the aerosol chemical composition, number concentrations and cloud condensation nuclei (CCN) abilities. For the first time, the application of CPMA together with an inversion method provided a new morphology independent measurement method to characterise the BC mixing state in the ambient atmosphere. Black carbon (BC) particles were found to be between an internal and external mixture in urban Beijing. The BC mixing state in urban Beijing was influenced by the air mass in winter, while no such strong correlation was found during the summer. For broader implications, the AAC combination provides the aerodynamic size-resolved measurement of both refractory and non-refractory composition in a suburb of Beijing. While organic matter accounted for a large fraction of particulate mass, a higher contribution of particulate nitrate at larger sizes was found in polluted conditions. The number fraction of BC was found to increase with aerodynamic diameter, and these thickly coated BC may act as source of CCN. This size regime in a polluted sub-urban environment may exhibit a higher deposition rate. Aircraft observations were performed over the Atlantic Ocean to measure the shipping emissions as part of the Atmospheric Composition and Radiative forcing change due to the International Ship Emissions regulations (ACRUISE) project. Sulfate was found to be an important contributor to the overall ship emitted aerosol compositions, and the reduction of fuel sulfur content (FSC) due to the new global emission regulation is estimated to reduce the CCN abilities of ship emitted aerosols significantly. However, the emission of less hygroscopic compounds, BC and organic matter, is less influenced by the change of FSC. In summary, the results from the new measurement techniques and methodologies in this work offer an in-depth insight into the physicochemical properties of anthropogenic aerosols. These key findings build the connection between the aerosol mixing state and cloud condensation nuclei activities. This increasing understanding of aerosol properties can contribute to the improvement of model simulations and the development of policies to mitigate the effects of anthropogenic pollution in future studies.