Characteristics Of Major Physical And Chemical Processes During Haze Day In Shanghai

Haze was caused by visibility reduction which was closely related to theaccumulation of not only primary particles but also secondary particles under alimited atmosphere capacity. The increase of haze not only affects traffic safety,public health and agricultural production, but also affects the global climate change.Atmospheric haze pollution has attracted global attention. Synchrotron radiationX-ray absorption fine structure (XAFS) is a very powerful technology in analysis ofPM with its low detection limit, high accuracy and the ability of in-situ detection. Inthis thesis, based on the actual atmospheric particulate matter (PM) sampling andsmog chamber experiments, the main physical (temperature inversion layer (TIL),relative humidity (RH), air mass trajectories) and chemical problems (sulfates, nitratesand ammonium (SNA) in PM, the formation of sulfates) during haze formation inShanghai were studied by combining XAFS, ion chromatography (IC) and X-rayfluorescence (XRF).Located on the Yangtze River estuary, the main terrain of Shanghai is plain. Thegeographical location of Shanghai could favor the diffusion of PM, but haze event hasoccurred frequently in Shanghai. The mass concentrations of all size-fractionated PMwere higher in haze days than in non-haze days and even higher in the size of0.49-0.95and0.95-1.5μm in Shanghai. High concentrations of SNA and(NH4)2SO4were oberseved in fine (<1.5μm) PM during haze episodes. Clusteranalysis of air mass backward trajectories was calculated in this thesis to evaluate theimpact of regional pollution on PM concentration and characteristics in Shanghai.Results revealed that there are six clusters of average air mass trajectories in Shanghai.Air masses with short backward trajectories from the Yangtze River delta (YRD)region (8%in a whole year) brought serious PM pollution for Shanghai. The study ofhaze pollution in Shanghai must consider the impact of pollution sources in the YRDregion. The analysis with backward trajectory and area pollution emissions sourcescan provide some scientific basis for the prediction of haze in Shanghai.Meteorological conditions determine an important indicator of air pollution, environmental capacity. The particulate emissions that exceed the environmentalcapacity will cause PM pollution. The inversely proportional relationship between thebase heights of TIL and PM concentrations in Shanghai was found in this thesis. Therelationship can be signified as Y=15000/(H-16)+36, where Y and H refers PM10concentration (μg/m3) and the base heights of TIL (m), respectively. As a mid-latitudecoastal city, TIL with low height often appears during winter in Shanghai, whichmight be an important reason why haze occur frequently in winter of Shanghai.Similarly, high RH, low wind velocity and low temperature would also lowerenvironmental capacity, accelerate the accumlation of PM and cause PMconcentration rise.As the main components of secondary inorganic aerosol, SNA are considered asone of the most important contributors to visibility impairment. Combined with airmass back-trajectories, the highest concentration of SNA in fine PM of Shanghai wasobserved during the periods of air mass stagnations. The method for speciation of theoxidation state of sulfur and different sulfate species in PM by sulfur K-edge x-rayabsorption near edge structure (XANES) were established. The PM samples duringhaze and non-haze episodes in Shanghai were analyzed by this method. Resultsrevealed that sulfur mainly existed as sulfate with a proportion (atomic basis) morethan73%in all size of PM and even higher as90%in fine particles. Sulfate mainlyexisted as (NH4)2SO4and CaSO42H2O in PM of Shanghai. Compared to non-hazedays, a dramatic increase of (NH4)2SO4content was found in fine particles on hazedays only, which suggested the promoting impact of (NH4)2SO4on haze formation. Inorder to study the formation mechanism of sulfate in PM during haze episodes, theheterogeneous chemical process of sulfate formation catalyzed by Fe-containingparticles under haze conditions was simulated and measured in-situ with synchrotronradiation XAFS techniques. Results indicated that the water content on the surface ofPM was very important, which suggested that high RH favored the secondary PMformation. Results also confirmed that this heterogeneous chemical process actuallytake place on the surface of PM. This result explained part of sulfate component source in PM during haze episodes.The results of this thesis can provide relevant theoretical and experimental basisfor the comprehensive assessment of haze formation in Shanghai.