Characteristics Of Hydrogen And Oxygen Isotopes In Atmospheric Water Vapor And Precipitation And Their Environmental Significances In Shanghai

The research on hydrogen and oxygen isotope composition and spatial and temporal variation of precipitation has been relatively mature.However,atmospheric water vapor,the precursor of precipitation,has become a hot spot and frontier of global change and environmental evolution due to its unique advantages in tracing precipitation sources and regional material transport.Compared with meteoric precipitation,the hydrogen and oxygen isotopes of water vapor are more sensitive to the changes of regional atmospheric elements and boundary layer conditions.Therefore,it is of great theoretical and application value to explore the influence of the above elements and to retrieve the recorded atmospheric environment information.This research collected water vapor samples and 90%precipitation samples of 6periods of time from winter of 2018 to winter of 2019 in Minhang,Shanghai.We measured the hydrogen and oxygen isotopes of the samples,and discussed the time-varying characteristics of water vapor?D,?¹⁸O and?¹⁷O and deuterium excess value?d?,their relationship with the meteoric precipitation line and the environmental indication significance;we explored in depth the reliability of tracing water vapor sources through variations in deuterium excess,?¹⁷O and?¹⁸O,and in particular,tracing the water vapor produced by human activities in the research area.Through the work of this thesis,the following conclusions are drawn:1.The variation characteristics of?D,?¹⁸O and?¹⁷O in the atmospheric water vapor in Shanghai are basically the same on different time scales,with no obvious diurnal variation and no obvious seasonal difference.The precipitation process will lead to the obvious negative deviation of isotopes in atmospheric water vapor.There was a good correlation with the latitudinal distribution pattern of water vapor:The hydrogen and oxygen isotopic values of water vapor in Shanghai are close to those in the observation stations of similar latitude,and are heavier than those in the stations of higher latitude.The d value of water vapor isotope in Shanghai observed in this study is significantly higher than that in other parts of the world,which is due to the frequent precipitation and low relative humidity of the atmosphere under clouds during the water vapor sampling period of this study,and the secondary evaporation of atmospheric precipitation will cause the increase of the d value of atmospheric water vapor.2.?¹⁸O and?D in atmospheric water vapor in Shanghai have a good correlation.Spring:?D=6.64?¹⁸O+6.47?n=84,r=0.97?Summer:?D=7.29?¹⁸O+13.25?n=81,r=0.98?Autumn:?D=3.58?¹⁸O–38.40?n=74,r=0.77?Winter:?D=8.12?¹⁸O+32.11?n=84,r=0.94?.Being similar to the precipitation data in Shanghai,the slope and intercept of these equations had the characteristics of lower in spring and autumn,higher in winter and summer.The difference between precipitation isotopes and water vapor isotopes in the same period had a strong positive correlation with the precipitation isotopes,which is related to the precipitation scale.Heavy precipitation and high relative humidity under clouds will inhibit the kinetic fractionation caused by secondary evaporation,thus reducing the isotope differences between precipitation and water vapor.The correlation between water vapor,hydrogen and oxygen isotopes and absolute humidity was the best,and this correlation was high in spring(r=0.88,correlation coefficient between?¹⁸O and absolute humidity,the same below),autumn?r=0.82?and winter temperature inversion period?r=0.91?,but not in summer?r=0.06?and winter non-inversion period?r=0.15?.3.The mean value of water vapor isotope d showed significant seasonal changes:winter?31.70‰?>autumn?30.13‰?>spring?27.08‰?>summer?25.75‰?.The d value in water vapor is higher than the precipitation in the same season,and the seasonal variation trend is basically the same.Except for the non-inversion period in winter,all the four seasons showed the rule that d value gradually decreased with the increase of relative humidity,and this correlation was the highest in the winter inversion period.This indicated that the water vapor source in the winter inversion period in Shanghai was relatively close,and local evaporation was the main factor,so it can reflect the relationship between d value and relative humidity.In the non-inversion period in winter,local water vapor dissipated rapidly,so the d value in this period showed a poor correlation with local relative humidity.4.In spring,summer and autumn,?¹⁷O and?¹⁸O in atmospheric water vapor basically followed the mass-dependent fractionation effect.The slope and intercept in the winter inversion period were smaller than the mass fractionation line,while in the winter non-inversion period they were larger.The fluctuation range of atmospheric water vapor?¹⁷O was larger than that of precipitation in Shanghai area.The group with the highest average value appears in winter inversion peroid,reaching 159.98 per meg,while the group with the lowest average value appears in winter non-inversion peroid,reaching-56.05 per meg.The standard deviations of samples in winter were obviously higher than that in other seasons,indicating that the water vapor source in Shanghai was relatively mixed.Since the Shanghai area is not in the region with strong exchange of stratosphere and troposphere,the abnormal signals of oxygen isotopes may come from the near-surface environment.5.The?¹⁸O of precipitation in the same period were higher than the water vapor,while the d values were lower than the water vapor.The seasonal variation trend of water vapor and precipitation?¹⁸O were basically the same,while the variation trend of d values was significantly different in the summer.The measured?D were close to the calculated values of equilibrium fractionation theory.The measured?¹⁸O were less than the theoretical values.The measured d values were obviously larger than the theoretical values,with the maximum difference reaching 19.91‰,and the differences of measured and theoretical d values had a certain negative correlation with relative humidity.6.The negative correlation between atmospheric water vapor d value and CO₂ in Shanghai in winter?r=-0.66,in the winter inversion period?was significantly higher than that in summer?r=-0.25?.It can be speculated that the low d value of water vapor generated by fossil fuel combustion resulted in the decrease of atmospheric water vapor d value.The deuterium excess formula of mixed air calculated by Rayleigh fractionation model showed that during the winter temperature inversion period,the combustion-derived water accounted for a maximum of 12.3%of the total water vapor in the boundary layer,and the average proportion was 7.5%.This result proved that the water vapor generated from anthropogenic fossil fuel combustion in Shanghai area occupies a large proportion in inversion peroid,and this part of water vapor may have a certain influence on the composotion of water isotopes in the atmosphere.