Study On Physicochemical Charateristics Of Individual Sea Salt Aerosol Particles In Polar Atmosphere

Climate change and atmospheric pollution have become one of the serious problems around the world. The environmental change of Arctic and Antarctic is the important "natural indicator" for the global climate change. Meanwhile, Arctic and Antarctic are also the "natural laboratory" to study the physical and chemical properties of atmospheric aerosols. The dominant particles in the Arctic and Antarctic atmosphere are sea salt aerosols (SSA), and SSA have an important impact on the polar solar radiative balance. In order to characterize SSA, we carried out three field experiments at the Chinese Arctic Yellow River Station, individual particle samples were collected on August 3-23,2012, April 28-May 15,2013, and September 3-22, 2013, respectively. Moreover, we collected aerosol samples during November 4, 2012-April 6,2013 from Shanghai, China to Antarctic. Using electron microscopy (e.g., transmission electron microscopy with energy-dispersive X-ray spectrometry (TEM/EDX), scanning electron microscopy (SEM), scanning TEM (STEM), atomic force microscopy (AFM)) and mass spectrometry (e.g., nanoscale secondary ion mass spectrometry (nanoSIMS)), we analyzed morphology, composition, size, and mixing state of individual SSA. Furthermore, we analyzed particles’source and transport pattern using the HYSPLIT model.Based on their morphology and composition, Arctic SSA were divided into fresh, partially aged, and fully aged SSA. Fresh SSA consisted of cubic NaCl coated by minor MgCl2 and CaSO4. Partially aged SSA consisted of irregular NaCl coated by a mixture of NaNO3, Na2SO4, Mg(NO3)2, and MgSO4. The comparisons suggest that the highly hydrophilic MgCl2 coating on fresh SSA can accelerate the heterogeneous reactions between SSA and acidic gases (e.g., H2SO4/SO2 and HNO3/NOX). Fully aged SSA with the round shape mainly contained Na2SO4 and NaNO3 and Cl in NaCl was completely depleted. In the Arctic, the fresh and partially aged SSA showed a unimodal distribution, and their peaks were 0.68μm and 1.30μm in August 2012, 1.10μm and 1.15μm in April and May 2013,0.9μm and 1.05μm in September 2013, however, fully aged SSA showed a broad size distribution, and the range were 0.9-2.0μm,0.81-1.30μm, and 0.99-1.50μm, respectively. These results suggested that particle ageing likely enhanced particle size.In this study, we specifically study individual SSA particles collected on August 3-23,2012 in Arctic. Back trajectories of air masses displayed that air masses mainly had two pathways:One originated from central Arctic Ocean (Group A) and other one from North America and Greenland (Group B). Fractions of the fresh, partially aged, and fully aged SSA are 43.07%,44.53%, and 12.41% in group A and 18.72%,47.45%, 33.83% in group B. Hygroscopic experiments show that the deliquescence points of the fresh, partially aged, and fully aged SSA are 69%,65%, and 60%, in addition, the efflorescence points are 50%、47%, and 49%, respectively. Elemental mappings of SSA particles displayed that Cl gradually depleted and the contents of S, O, C, and N increased from fresh to partially aged to fully aged SSA. In comparison to fresh SSA, nanoSIMS mappings showed that nitrate and organic matter (OM) increased in aged SSA. Moreover, 12C- and 12C14N- line scans indicated OM mainly distributed on the aged SSA surface. Interestingly, number of mineral dust particles obviously increased on August 20,2012, which most of mineral particles were submicron and fresh. Based on the back trajectories of air mass, the mineral dust likely originated from the northern Greenland island.SSA are the dominant particles in the atmosphere from China to Antarctic. The highest ratio (100%) for SSA was in the Indian Ocean, while the lowest ratio (51.38%) was in the Antarctic continent. In Antarctic coast and Australia’s western coast,18.33% and 16.28% particles were mineral dust from natural land soil. In Anrarctic continent, S-rich particles content (20.31%) was the highest.This thesis studied individual SSA particles in detail collected in Arctic and Antarctic navigation process, which not only provided a reliable data for heterogeneous chemical reaction between SSA and inorganic acids in the atmosphere, but also initially proved that SSA reacted with organic acids. The new findings produced a theoretical basis for calculating the global atmospheric chemical model and climate effect about SSA particles.