AMS Measurement Of ¹⁴C And Its Application For PM2.5 Source Apportionment

In recent years, fog and haze phenomenon happened frequently with the rapid economic development and urbanization in some areas, and it has become one of the most important environmental factors which affect our lives and health.Studies have shown that about 50%-70% of the contaminated ingredient associated with carbonaceous of biomass and fossil sources in the atmospheric PM2.5 sources. Fossil source refers to coal, oil, natural gas and other fossil fuel combustion contribution to atmospheric PM2.5, which is part of the pollution due to 14C after a long period of decay, so the content is very low, the value of 14C/12C of about 10-15-10-16 magnitude; biological source refers to modern biomass burning contribution to the atmosphere of PM2.5, values such as straw burning, city barbecue smoke etc. produce 14C/12C of about 1.2×10-12. As a result, the accurate measurement and analysis of 14C is very important for the PM2.5 source apportionment.This work relies on the 200 kV single stage electrostatic accelerator mass spectrometer (GXNU-AMS) built by the cooperation with Guangxi Normal University and China Institute of Atomic Energy. A series of PM2.5 aerosols samples of Beijing were analyzed by this AMS system. This work mainly including as follows:(1) The process of establishment and improvement of 14C sample preparation. A series of jobs were carried out based on the conceptual principles of existing laboratory sample preparation system which include of hydrogen, zinc and zinc-hydrogen methods and so on. The samples preparation mainly refer the aims sample processing method, overcome small beam current, low yield, eliminate interference and reference materials preparation.(2) 14C-AMS optimization and realize its highly efficiency and precision measurements which including:debug of ions extraction, ions transmission, measurement technique, and background exclude. As a result, the optimization condition of 14C and its isotopes precision measurement was obtained finally.(3) The source apportionment work of Beijing PM2.5 was carried out. A series of PM2.5 samples of near Beijing Huai Rou and Jian De Men collected during June 20 to July 10,2015 and Chao Yang District in the period of late October 2014 was analyzed based on this improved method, smoothly.Several of achievements were obtained:(1) The 14C samples preparation was set up successfully for the measurement of GXNU-AMS. As a result, the final yield of over 90%, the beam current of 15μA—25μA, samples preparation background of lower 6×10-15,about 100μg graphite extracted were realized;(2) A kind of new method of low-temperature catalyst used separation and extraction of PM2.5 OC/EC of atmospheric samples, successfully; (3) the optimum experimental conditions of 14C and its isotopes with GXNU-AMS was determined, and the determination sensitivity of 5×10-15 and analysis accurate of 1.2% was obtained; (4) The pollution contribution of fossil and biological source in specific area and period for different time periods, different regions, different locations of day and night, and the same place of long period were obtained intuitively and effectively. Based on these, this work lays a scientific foundation for the atmospheric PM2.5 and the research of secondary aerosols mechanism.