[Comparison of Characteristics and Reactive Oxidative Species of PM in Xi'an, China During Haze and Clean Days].

PM samples were collected in Xi'an, China during haze(2015-11-30-2015-12-9) and clean days(2016-01-13-2016-01-22). PM mass, organic carbon(OC), elemental carbon(EC), and water-soluble ions(i.e., NH, NO, and SO) were measured to investigate the characteristics of the two typical pollution processes. The result showed that PM masses were(170±47.5) μg·m and(48.6±17.9) μg·m for the haze and clean days, respectively, with the haze accompanied by low visibility, high humidity, calm wind, and other adverse weather conditions. The secondary inorganic aerosol(SIA) including NH, NO, and SO accounted for 49.8%±13.1% and 19.4%±5.95% of the PM mass for the haze and clean days, respectively. sulfur and nitrogen oxidation ratios(SOR and NOR) on haze days were 0.282±0.157 and 0.269±0.124, respectively, which were much higher than those measured on the clean days(0.189±0.057 and 0.077±0.046). The average concentration of secondary organic carbon(SOC) for the haze days(6.22±3.87) μg·m was 5 times of that measured in the clean days(1.44±1.63) μg·m. Secondary pollution and adverse weather conditions were the main reasons for the heavy haze. Finally, the level of particulate-Reactive Oxygen Species(ROS)was measured by the 2',7'-dichlorofluorescin diacetate(2',7'-DCFH) fluorescence method, and the average ROS concentration (as HO) was(4.99±1.54) nmol·m during haze days and(0.492±0.356) nmol·m during clean days. Accumulation effect and secondary oxidation process may be the main reasons for the increase of ROS concentration under the heavy haze conditions in Xi'an. Positive correlations(<0.05) between the concentrations of ROS and the ions of NO and SO indicated that ROS may participate in secondary oxidation process of SIA.