海水中二甲基硫的光化学动力学过程及影响因素研究

发布时间：2018-02-20 16:28

本文关键词： 二甲基硫光化学降解光照波段有色溶解有机物东海　出处：《中国海洋大学》2014年硕士论文　论文类型：学位论文

【摘要】：二甲基硫（dimethylsulfide，DMS）是海水中最重要的挥发性生源硫化物，其在大气中的氧化物会对全球气候的变化和酸雨的形成产生重要的影响。在海水中DMS的迁移转化中，光化学氧化是海水中DMS的主要去除途径之一，是影响海水中DMS浓度和海-气通量的重要因素，同时此过程又会受到各种复杂条件的影响，因此，有关海水中DMS的光化学降解过程及其影响因素的研究对于全面认识海洋中DMS的生物地球化学循环过程及其环境效应具有重要的意义。本论文采用实验室模拟和海洋现场调查相结合的方式，实验室模拟是以氙灯为光源，探讨了DMS在UVB （280、295和305nm）、UVA（320、345和395nm）、和可见光（435和495nm）8个不同波段下的光化学降解行为及影响因素。海上的现场测定是在中国东海开展甲板培养实验，研究海上现场DMS光氧化的情况，然后进一步将DMS的三个移除途径光化学氧化、生物消费、海气扩散结合到一起，研究之间的相关联系。主要研究结果如下：（1）DMS光降解反应基本符合一级反应动力学（ln(Ct/C0)=-kt），且在不同光照波段下DMS的光降解速率不同。在研究波段范围内，DMS在UVB各波段区的降解速率明显大于UVA和可见光区各波段的速率，且在280nm下DMS光降解速率最大。有色溶解有机物（CDOM）在DMS光化学降解中起到一个非常关键的作用，太阳能辐射和CDOM之间的相互作用是活性分子的主要来源。在8个不同波段下，随着光照时间的增长，海水中CDOM的光谱吸收系数随之增大，并受到光照波段的影响，其中在280nm下光谱吸收系数最大。另外，CDOM光谱吸收系数与DMS浓度有很好的线性拟合，说明CDOM的吸光特性会明显影响DMS的光化学降解过程，并且不同光照波段影响有所差异。 8个不同光照波段280、295、305、320、345、395、435和495nm下，分别光照6h后DMS光化学氧化向二甲亚砜（DMSO）的转化率分别是31.3%、28.2%、25.5%、22.5%、27.4%、29.6%、20.4%和24.1%。由此结果可以看出，DMS在UVB波段向DMSO的转化率较大，且在280nm下达到最大值。（2）于2013年6月21日-7月22日（夏季）对东海海域中DMS的浓度分布以及迁移转化进行了研究。结果表明夏季东海表层海水中DMS的浓度变化范围比较大，主要是4.78（1.16-11.61）nmolL-1。对于水平分布来说，总体上呈现出近岸高、外海低的分布趋势，由此看出，人为活动对DMS生物生产以及浓度分布有着深刻的影响；夏季东海表层海水中DMS的浓度与Chl-a浓度之间具有良好的相关性，由此可见，在控制东海表层海水中DMS浓度方面，浮游植物的生物量起着重要的作用。东海7个调查站位的海水中DMS光化学降解速率与实验室模拟结果是一致的，均是在UVB波段下的光氧化速率最快，在可见光波段下氧化速率最慢，而且近海站位的DMS光降解速率要明显高于中间陆架站位以及远海站位，表明在DMS的光化学降解过程中CDOM是主要的光敏剂，，近海站位由于陆源的输入导致CDOM含量要显著的高于中间陆架以及远海的含量。在东海表层海水中，光化学氧化和微生物消耗这两种去除途径所需要的周转时间大约一致，都在1d左右，而海－气扩散这一途径的周转时间比较长，需要几天左右，由此可知，光化学氧化与微生物降解在DMS迁移转化的过程中具有同样的重要性，因此光化学氧化是海水中DMS去除的主要途径之一，在DMS的迁移转化过程中扮演着极为重要的作用。将东海站位海水的实验室模拟与黄海站位海水的实验室模拟结果比较发现，东海站位海水中DMS的光化学氧化速率比黄海站位海水中DMS的氧化速率要慢，虽然在这两次实验室模拟的过程中，DMS的初始浓度、光照波段以及光照强度等因素都是相同的，但是在不同海区的海水中物质的结构和组成不同的。进一步说明表层海水中DMS的光降解过程是一个复杂的动态过程，其反应速率受到光照波段、CDOM的性质和分布以及海区环境等多方面的影响。
[Abstract]:Dimethyl sulfide ( DMS ) is one of the most important volatile compounds in seawater , and its oxides in the atmosphere have an important influence on global climate change and acid rain formation . In the migration and transformation of DMS in seawater , photochemical oxidation is one of the main ways to remove DMS and sea - gas flux in seawater . In this paper , the chemical degradation behavior and influencing factors of DMS on UVB ( 280 , 295 and 305 nm ) , UVA ( 320 , 345 and 395 nm ) , UVA ( 320 , 345 and 395 nm ) , and visible light ( 435 and 495 nm ) in 8 different wavelength bands were studied by means of laboratory simulation and ocean site investigation . ( 1 ) DMS photodegradation reaction basically accords with first - order reaction kinetics ( ln ( Ct / C0 ) = - kt ) , and the degradation rate of DMS under different illumination wavebands is different . In the range of the research band , the degradation rate of DMS in each wavelength band of the UVB is obviously higher than that of UVA and visible region , and the DMS light degradation rate is the maximum at 280 nm . CDOM plays a very important role in the photochemical degradation of DMS . The interaction between solar radiation and CDOM is the main source of active molecules . In 8 different wavebands , the spectral absorption coefficient of CDOM increases with the increase of illumination time . The absorption coefficient of CDOM is the largest at 280 nm . The conversion rate of DMS photochemically oxidized to dimethyl sulfoxide ( DMSO ) at 6280 , 295 , 305 , 320 , 345 , 395 , 435 and 495 nm in 8 different illumination bands was 31.3 % , 28 . 2 % , 25.5 % , 22.5 % , 27 . 4 % , 29 . 6 % , 20.4 % and 24.1 % , respectively . As a result , it can be seen that the conversion rate of DMS to DMSO in UVB band was large and reached its maximum at 280 nm . ( 2 ) From June 21 to July 22 , 2013 ( summer ) , the concentration distribution and migration transformation of DMS in the sea area of East China Sea were studied . The results show that the concentration of DMS in the surface water of East China Sea is relatively large , mainly 4.78 ( 1.16 - 11.61 ) nmolL - 1 . The chemical degradation rate of DMS in the seawater of 7 stations in the East China Sea is consistent with the laboratory simulation results , which are the fastest in the UVB wavelength band , the lowest oxidation rate in the visible light wave band , and the DMS light degradation rate in the near sea level is obviously higher than that of the intermediate shelf station and the far sea station , indicating that the CDOM is the main photosensitizer in the photochemical degradation of the DMS , and the content of the CDOM is higher than that of the middle shelf and the far sea due to the input of the land source . In the sea water of the East China Sea , the turnaround time required for both photochemical oxidation and microbial consumption is around 1d , and the turnaround time of sea - gas diffusion is relatively long . It can be seen that photochemical oxidation and microbial degradation are of the same importance in the process of DMS migration and transformation . Therefore , photochemical oxidation is one of the main ways of DMS removal in seawater , which plays an important role in DMS migration and transformation . It is found that the chemical oxidation rate of DMS in the seawater of the East China Sea is slower than that of the DMS in the seawater of the Yellow Sea . Although the initial concentration , the illumination wavelength band and the light intensity of the DMS are the same in the process of the two laboratory simulation , the photodegradation process of DMS in the sea water is different . The reaction rate is influenced by the nature and distribution of the illumination wavelength band and CDOM and the environment of the sea area .

【学位授予单位】：中国海洋大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P734

【参考文献】