Study On The Distribution And Regional Transport Of Trace Gases And Aerosol Over YRD Region Based On MAX-DOAS

With severe regional air pollution problem in China,grasping the concentration of air pollutants and their distribution information timely and accurately is the prerequisite for effective control of air pollution.Traditional atmospheric environmental monitoring technology mainly relies on the urban air quality automatic monitoring station,but the number of monitoring points is limited.It can not achieve effective coverage of urban fringe areas,nor can it fulfill the requirement of research need in the vertical evolution process of air pollution.Multi-Axis Differential Optical Absorption Spectroscopy(MAX-DOAS)is a passive remote sensing technique providing indispensable information of atmospheric aerosols and trace gases.MAX-DOAS observations are not only limited to ground based application,but also can be performed on mobile platforms to obtain temporal and spatial distribution information of trace gases in regional scale.In this thesis,we present MAX-DOAS measurements of tropospheric trace gases and aerosol distribution in the Yangtze River Delta region during wintertime.We take NO2?SO2?HCHO and aerosol as the research object to discuss their temporal and spatial distribution,vertical structure as well as transport characteristics.The main conclusions are as follows:1.During Yangtze River Campaign,ship-based MAX-DOAS measurements of tropospheric vertical column densities(VCDs)of NO2,SO2,and HCHO were performed along the Yangtze River.Three elevated tropospheric NO2 and SO2 VCDs events over Yangtze River were detected around three major industrial cities with large number of heavy emission sources.Positive correlations were found between concentration of NO2 and SO2 VCDs and wind speed over these areas,which means that the transport from high-emission upwind areas along Yangtze River is more significant than of the contribution from local emission sources.2.Ship-based MAX-DOAS measurements of tropospheric NO2 are used to validate OMI tropospheric NO2 products.Compared to the NASA's standard product,the USTC's OMI tropospheric NO2 VCD agrees better with ground measurements a Pearson correlation coefficient(R)of 0.82 while the correlation between MAX-DOAS and the NASA OMI product is 0.76.However,the regression analysis indicated that the USTC's and NASA's OMI data underestimated the tropospheric NO2 VCD by about 10%and 27%,respectively.3.NO2/SO2 ratio was used to estimate the relative contributions of industrial sources and vehicle emissions to ambient N02 levels.Analysis results of NO2/SO2 ratio shows that higher contribution of industrial NO2 emissions in Jiangsu province,while NO2 levels in Jiangxi and Hubei provinces are mainly related to vehicle emissions.These results indicate that different pollution control strategies should be applied in different provinces.4.Multiple linear regression analysis of ambient carbon monoxide(CO)and odd oxygen(Ox)indicated that the primary emission,secondary formation and background contributions of HCHO contribute 54.4±3.7%,39.3±4.3%and 6.2±0.8%to the ambient HCHO,respectively.The largest contribution from primary emissions in winter suggested that photochemically induced secondary formation of HCHO is reduced due to lower solar irradiance in winter.5.Ground-based MAX-DOAS measurements were performed in the wintertime of Hefei to provide information on the vertical distribution of aerosol extinction and trace gases(e.g.,NO2,SO2 and HCHO)in the lower troposphere.Both aerosol and N02 show exponentially decreasing profile.The profile shape of aerosol and N02 can be mostly attributed to its near-surface emission sources.The S02 and HCHO layer are found at a higher altitude compared to aerosol and N02.SO2 in the middle layer account for 92.46%of that in the lower layer.A possible explanation for this is that SO2 is emitted predominantly from elevated point sources(e.g.,power plants),which can bring high S02 concentrations in the middle layer.Elevated HCHO is observed in the middle layer during noon where HCHO concentration was 120%of that in the lower layer,probably indicating that the larger effect of the photochemical formation of atmospheric HCHO rather than direct HCHO emissions.6.The aerosol extinction coefficient during haze days was in general?17.72±7.37±%higher than that of clar days,which might be related to the poor mixing and dispersion conditions on haze days.Compared to clear days,higher growth rate of aerosol extinction(?25%)is observed at?0.2-0.4 km.The growth rate of NO2 at the ground level(0-0.2 km)is lower than 10%,and growing steadily as the altitude increases(up to 1.2 km),followed by a decrease above 1.2 km.Moreover,higher growth rate of SO2(20-42%)is observed from the surface to 0.6 km.Compared to clear days,higher growth rate of HCHO(-40%)is observed from 0.6 to 1 km during haze days.These phenomenons indicate the importance of long-distance transport of NO2,SO2 and longer-lived precursors of HCHO during haze days in Hefei.7.Potential source contribution function(PSCF)and concentration-weighted trajectory(CWT)models were used to evaluate the potential sources of Hefei''s air pollution in the lower,middle and upper boundary layer.The results revealed that the northern and eastern part of Anhui was recognized as the area contributing the most NO2 in the lower layer.Transported SO2 from the northwestern regions in the middle layer made great contribution to SO2 in Hefei.HCHO was mostly produced locally while the transport of HCHO from potential source areas was negligible.Local area and the northeastern part of Anhui,with rather high WCWT values(-0.4 km-1),was recognized as the area contributing the most aerosol in the lower altitude of Hefei.During heavy pollution episodes,the highest averaged growth rate of aerosol are observed in an altitude of?400 m.PSCF and CWT analysis for heavy haze episodes suggested that the potential source areas for aerosol were almost located in the northern region,the northwestern region,and the YRD region.