CHOCHO,HCHO And NO₂ Monitoring In Beijing-Tianjin-Hebei And Yangtze River Delta Regions,Using Ground-based MAX-DOAS Observations

Air pollution has become an incessant problem of the modern day and has grabbed attention of various scholars and scientists.The problem has emerged as one of the major environmental issues worldwide.The importance of the problem lies in the broad impacts that it holds not only on the environment but also on public health.For China,it has become the most pressing environmental concern mainly because of the fast growing economy,rapid industrialization and other anthropogenic activities.Ground based Max-DOAS observations of CHOCHO,HCHO and NO2 were done over different cities of China.The first part of thesis focused on optimization of settings for the retrieval of CHOCHO from MAX-DOAS.The different sensitivity tests were done to optimize the fit parameters.The root mean square of residual and Differential Slant Column density(dSCD)error was reduced when measurements were done with lower wavelength limit around 432-438 nm and upper intervals around 455-460 nm.Thus,lower wavelength intervals around 432-438 nm and upper intervals around 457-460 nm were best for the retrieval of dSCDs for CHOCHO.The effect of different Meteorological conditions was examined on concentration of CHOCHO and NO2.The average concentration of NO2,CHOCHO and PM 2.5 during Haze Days is larger as compared to Clear days.Higher levels of trace gases were observed in Beijing most likely due to higher economic and industrial activities at Beijing.Seasonal variation categorized by wintertime maxima and summertime minima was observed for CHOCHO,while for HCHO maximum values were recorded during summer.Variations in the diurnal cycle of trace gases were examined;the results indicated a strong link to Photo-oxidations of VOCs for HCHO production,whereas the CHOCHO diurnal variation can possibly be related to anthropogenic effect in the evening.The Weekend didn’t have any significant effect on both HCHO and CHOCHO.We investigated the temperature dependency of HCHO and CHOCHO.HCHO shows positive correlation with air temperature at both monitoring stations,which strengthened the argument that HCHO production is linked to photo-oxidation of VOCs.CHOCHO is anti-correlated with air temperature at both observation sites suggesting that photolysis is major sink for CHOCHO at Beijing and Baoding.We also investigated the ratio of CHOCHO to HCHO(RGF)as a gauge to obtain information regarding VOCs precursors.RGF was compared with EVI data obtained from MODIS,which represents direct relation with Biogenic emissions.The RGF showed higher values in winter and autumn as compared to spring and summer when higher levels of EVI were observed.Therefore Higher RGF values correspond to anthropogenic emissions and Lower RGF corresponds to Biogenic emissions.The strong correlation of HCHO with EVI suggests oxidation of isoprene and HCHO production are strongly related.