【作者】 林立；

【导师】 陈建民；

【作者基本信息】 复旦大学 ， 环境科学， 2010， 硕士

【摘要】 大气气溶胶对城市空气污染、大气环境乃至全球气候的影响很大,它为痕量气体如SO2,NOX,NH3,H2S,CHx等提供了巨大的反应床和储存库,同时增加了通过太阳辐射和一些复杂化学反应而产生二次气溶胶的可能性。近年来,中国大陆机动车保有量不断增加,从而造成NOx、颗粒物、VOCs等的排放量日益增加,尤其是诸如北京、上海、广州等特大型城市的大气污染日益严重。已有研究表明,大气中HNO3(g),NO2(g),N2O5(g),ClONO2(g)等能在大气颗粒物表面发生非均相化学反应而生成硝酸盐。现场监测表明,世界上不同地区的海盐及矿尘气溶胶中都含有硝酸盐,含硝酸盐的海盐又会与从干旱和半干旱地区传输过来的矿尘气溶胶混合形成含硝酸盐混合气溶胶。硝酸盐的存在会很大程度上改变原有气溶胶的表面性质,并影响其反应活性。因此,研究硝酸盐如何影响大气SO2的非均相反应以及含硝酸盐气溶胶的反应机制意义重大。目前,大部分文献是关于SO2在典型矿尘气溶胶表面,如中国黄土、合成海盐以及撒哈拉矿尘表面发生的非均相反应,而对于硝酸盐如何影响SO2在大气气溶胶表面上的非均相反应的关注很少,迄今为止还没有人研究过含硝酸矿尘气溶胶与SO2发生非均相化学反应的机制。因此,我们需要更好地理解矿尘及硝酸盐混合气溶胶与大气中痕量气体的非均相化学反应。本论文主要利用流动态的原位傅立叶红外漫反射光谱仪(DRIFTS)对硝酸盐和α-Fe2O3的混合颗粒物以及真实大气颗粒物表面与SO2的非均相反应进行研究,并同时比较了硝酸盐和其他金属氧化物的混合颗粒物与SO2反应的情况。论文主要结论如下：一研究了NH4NO3和α-Fe2O3混合颗粒物与SO2的非均相反应,并同时比较了NH4NO3和其他金属氧化物(CaO、MgO、α-Al2O3、SiO2)与SO2反应的情况。实验结果表明,NH4NO3和α-Fe2O3混合颗粒物较NH4NO3和其他金属氧化物混合颗粒与SO2的反应吸附系数高,表明α-Fe2O3催化能力比其他金属氧化物强。利用BET面积作为反应活性表面积,发现含有6%NH4NO3的NH4NO3和α-Fe2O3(W/W)混合颗粒物与SO2反应具有最高的γBET(2.42×10-9),相比纯α-Fe2O3的反应高了近1.8倍。而纯NH4NO3颗粒与SO2不发生反应,少量NH4NO3的存在在一定程度上提高了SO2在气溶胶颗粒物表面转化成硫酸盐的能力。二研究了不同质量百分含量的NaNO3和α-Fe2O3混合颗粒物与SO2反应。实验结果表明,SO2能在NaNO3和α-Fe2O3混合颗粒物表面生成吸附的硫酸盐并在气相生成了N2O及HNO3气体。纯NaNO3与SO2无反应,而NaNO3和α-Fe2O3混合颗粒物与SO2反应的BET吸附系数范围处于3.68×10-10到3.22×10-9之间,混合颗粒物的反应活性都比α-Fe2O3要高。60%NaNO3和α-Fe2O3混合颗粒物具有最高的反应活性,反应吸附系数是α-Fe2O3的8.7倍,NaNO3存在在很大程度上促进了SO2在氧化铁表面的氧化作用。三研究了含其他硝酸盐(如KNO3、Ca(NO3)2等)的混合颗粒物对SO2气-粒转化的影响作用,KNO3使SO2在颗粒物表面转化为硫酸盐的量大大增加而硝酸钙对其完全抑制,这部分内容完善了不同含硝酸盐气溶胶与SO2反应情况的研究体系。其次考虑了其他因素对含硝酸盐气溶胶与SO2反应的影响作用,其中包括有机物HCHO对NaN03-a-Fe203混合颗粒物与SO2反应的影响,结果表明CH3CHO、HCHO对该非均相反应有强烈的抑制作用。四研究了真实颗粒物(China Loess中国黄土和大气中降尘)与SO2反应的情况,反应生成微量的硫酸盐,表明真实颗粒物中也存在类似实验室模拟化学反应的情况,因此本论文具有一定的现实意义。更多还原

【Abstract】 Atmospheric aerosols contribute a lot to the urban pollution and affect the atmospheric environment and global climate as well.Aerosols provide large reservior for trace gases(SO2,NOx, NH3,H2S,CHx) and also act as highly reactive platform for them,thus enhancing the probability of forming secondary aerosols through solar radiation or complicated chemical reaction.With the development of economy and transportation, the amount of NOx, particles and VOCs emitted by automobile is increasing rapidly in mainland of China in recent years, especially in metropolis, such as Beijing, Shanghai and Guangzhou, the atmospheric pollution of which are much more serious.Research results show that atmospheric HN03(g), NO2(g), N2O5(g), ClONO2(g) can form nitrate on the sea-salt and mineral dust through a series of heterogeneous reaction.Field measurements showed that both sea-salt and mineral dust particles collected in different regions of the world are often found to be associated with nitrate.Since nitrate is always associated with mineral dust and sea-salt in the real atmospheric particles, and sea salt is believed to mix with mineral dust transported from arid and semiarid regions, the existence of nitrate salt particles may make the surface properties of nitrate-containing mineral particles much differently than those of previous particles and may impact its reactivity, it is reasonable to anticipate that the nitrate should influence the heterogeneous oxidation of atmospheric SO2, and it is very significant to investigate the reactivity of particles containing nitrate.However, most studies of heterogeneous reaction of SO2 focus on the surface of typical mineral oxides, China Loess, synthetic sea salt and Saharan mineral.In fact, little attention was paid to the influence of nitrate on the heterogeneous reaction of SO2 with atmospheric aerosols, and no one investigated the heterogeneous reactivity of SO2 on mineral particles containing nitrate up to now. A better understanding of the heterogeneous reaction of trace gases in the mixture of mineral dust aerosols and nitrate is therefore highly desirable.Heterogeneous oxidation of the gaseous SO2 on nitrate and Hematite mixtures compared to other metal oxides-nitrate mixtures along with the real particles (China Loess and atmospheric dust)were first studied using an in suit diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS).Main results are as followed.Firstly, heterogeneous oxidation of gaseous SO2 on ammonium nitrate containing Hematite particles compared to other ammonium nitrate-containing oxides (MgO, Al2O3,CaO, SiO2)were studied.Obvious sulfate(SO42-)formation can be seen from the infrared spectrum of nitrate-containing oxides, and the catalytic activity of Hematite is much higher compared to other oxides.Using BET area as the reactive surface area, the Hematite sample containing 6% of NH4NO3(W/W) presents the highestγBET value (2.42×10-9),which increases by a factor of 1.8 compared to that of Hematite.No formation of sulfate is observed on the pure NH4NO3.Secondly, Heterogeneous uptake of SO2 on Hematite in the presence of sodium nitrate at ambient temperature was studied.It is found that SO2 can undergo heterogeneous reaction to form adsorbed sulfate on the surface of Hematite-nitrate mixtures and evolve some other species in the gas phase, such as a small amount of N2O and HNO3.No uptake of SO2 and formation of sulfate were observed on the pure NaN03.The initial uptake coefficient calculated using the BET surface areas of the mixture samples ranged from 3.68×10-10 to 3.22×10-9.The reactivity of Hematite-nitrate mixtures was higher than that of Hematite solely. The 40% w/w Hematite+60% w/w NaNO3 sample presented the highest reactivity, its correspondingγBET was about 8.7 times larger than that of Hematite.These results clearly indicate that the presence of nitrate promoted the reactivity of samples and leaded to an increase in the uptake and oxidation of SO2 to sulfate in Hematite particles.Thirdly, heterogeneous oxidation of gaseous SO2 on other nitrate-containing (KNO3,Ca(NO3)2) Hematite particles compared to NH4NO3 and NaNO3 were studied. KNO3 enjoys the highest reactivity while Ca(NO3)2 completely impedes it. Furthermore, we also discussed some other factors that would affect the above reaction, including that organic compounds (HCHO and CH3CHO) impede the above reaction.Finally, Real particles (China Loess and dust) reacting with gaseous SO2 were discussed.Small amount of sulfate formed on the particles, which manifested the real meaning of this research.更多还原