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题名: 用于源解析的部分有机示踪物的大气稳定性研究
作者: 赖承钺
学位类别: 博士
答辩日期: 2015-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 贺泓
关键词: 大气稳定性 ; 有机示踪物 ; OH 氧化 ; 左旋葡聚糖 ; 脱氢松香酸 ; 蒎酮酸,atmospheric stability ; organic tracers ; OH radical oxidation ; levoglucosan ; dehydroabietic acid ; cis-pinonic acid
其他题名: Atmospheric Stability of Some Organic Tracers Used for Source Apportionment
学位专业: 环境科学
中文摘要:     有机气溶胶占据了大气细粒子的50% - 80%。其来源既包括一次的,也包含了相当数量的二次来源。源解析技术是定量识别气溶胶来源的重要手段。由于对污染源具有较强的特征性,有机示踪物被广泛应用于源解析研究中。源解析模型的一项基本假设是各种示踪物在大气中应当足够稳定。但是已有少量研究指出,一些常用于源解析的有机示踪物与大气氧化剂之间有较高的反应活性,从而对源解析结果的准确性带来较大的影响。这一现象已在大气环境化学领域引起了广泛的关注。但是目前对源解析模型中使用的示踪物的降解行为研究还非常有限;对同一示踪物,不同研究者测定的降解动力学尚存在数量级的差别;且现有研究尚
未充分考虑相对湿度、温度以及颗粒物混合状态等环境因素的影响。因此,本论文选取了生物质燃烧排放有机气溶胶示踪物(左旋葡聚糖和脱氢松香酸)和生物源二次有机气溶胶示踪物(蒎酮酸),使用流动反应装置研究了它们在不同环境条件下与大气氧化剂OH 自由基的非均相反应,并对它们的大气稳定性进行了讨论。
    本文首先在40%的相对湿度以及25 °C 的温度下研究了左旋葡聚糖、脱氢松香酸和蒎酮酸与OH 自由基的反应活性。结果表明,上述示踪物与OH 自由基的反应均比较显著,二级反应速率常数k2 分别为(9.17 ± 1.16)×10-12、(5.75 ±0.57)×10-12 以及(6.17 ± 1.07)×10-12 cm3·molecule-1·s-1。
    在真实大气环境下,各种理化性质均会对有机示踪物的大气行为产生影响。不同示踪物由于水溶性存在差异,它们的大气稳定性随湿度的变化也呈现出了不同的趋势。随着相对湿度的增加,左旋葡聚糖与OH 自由基的二级反应速率常数有较大幅度的下降;蒎酮酸与OH 自由基反应的速率常数仅有小幅降低;脱氢松香酸与OH 自由基的反应速率常数则基本没有变化。三种示踪物与OH 自由基的反应速率常数随温度的升高均有增大,温度与速率常数的关系符合阿仑尼乌斯方程。左旋葡聚糖、脱氢松香酸、蒎酮酸与OH 自由基反应的活化能分别为16.0 ±2.2、12.5 ± 0.5 以及14.4 ± 2.8 kJ·mol-1。与不同颗粒物混合后,左旋葡聚糖、脱氢
松香酸的大气稳定性有显著变化。当与无机盐混合时,两种示踪物与OH 自由基用于源解析的部分有机示踪物的大气稳定性研究的反应活性与混合方式有关;当与黑碳颗粒混合时,示踪物与OH 自由基反应的速率常数与纯样品相比显著降低,表明黑碳的混合会使得一次排放有机示踪物的大气稳定性明显增加。
    利用衰减全反射红外光谱以及气相色谱-质谱,辅之以DFT 理论计算,研究了示踪物被OH 自由基氧化后可能的产物。此外,通过测得的反应速率常数,计算了示踪物的大气寿命,得到不同环境条件以及不同混合状态下左旋葡聚糖的大气寿命为1.2-3.9 天、脱氢松香酸的大气寿命为2.3-4.7 天、蒎酮酸的大气寿命为2.1-3.3 天。由于示踪物最长的大气寿命依旧短于气溶胶本身的大气寿命,因此外场观测中测得的示踪物浓度可能会被低估,从而给源解析的结果带来负误差。本文研究不仅有助于了解有机气溶胶本身的大气环境行为,也将对现有源解析研究结果的改善提供基础数据。
英文摘要:     Organic aerosols take up 50% - 80% fractions of fine particles in the atmosphere which contain both primary and secondary sources. Source apportionment technique is an important way for the quantitative identification of aerosols. Recently, organic tracers have become more and more commonly used as source indicators due to the fact that they are specific to the sources of pollutants. A basic assumption in source apportionment models is that the tracers should be stable enough to persist in the atmosphere. However, a few studies have indicated that some organic tracers show high reactivity toward atmospheric oxidants, which will lead to significant impacts on the veracity of source apportionment results. This phenomenon has attracted much attention in the field of atmospheric environmental chemistry, but previous studies which focused on the degradation behaviours of organic tracers used in source apportionment models are limited, and some results vary on the magnitude of the effect for a specific tracer. Also, the effects of environmental conditions, such as relative humidity, temperature and the mixing states, were rarely taken into account. Therefore,in this dissertation, two biomass burning organic tracers (levoglucosan and dehydroabietic acid) and one biogenic secondary organic tracer (cis-pinonic acid) have been chosen. The heterogeneous reactions between such tracers and atmospheric oxidants (OH radicals) have been measured under different environmental conditions using a flow reactor.
    The atmospheric stability of levoglucosan, dehydroabietic acid and cis-pinonic acid in the presence of OH radicals at 40% relative humidity (RH) and 25 °C was investigated first. The results indicated that all the chosen tracers showed high reactivity towards OH radicals, with the second-order rate constant (k2) measured to be (9.17 ± 1.16)×10-12 cm3·molecule-1·s-1 for levoglucosan, (5.72 ± 0.87)×10-12 cm3·molecule-1·s- 1 for dehydroabietic acid and (6.17 ± 1.07)×10-12 cm3·molecule-1·s-1 for cis-pinonic acid, respectively.
    In the real atmosphere, chemical and physical characteristics will influence the atmospheric behaviors of organic tracers. Due to different solubilities in water, the atmospheric stability of different tracers showed diverse trends with changes in relative
humidity (RH). The k2 of levoglucosan toward OH showed the largest decay with increasing RH, while cis-pinonic acid showed only a slight decrease and dehydroabietic acid showed almost no variation. As for the temperature effect, the k2 of all the organic tracers towards OH increased with increasing temperature and followed the Arrhenius equation with the activation energy to be 16.0 ± 2.2 kJ·mol-1 for levoglucosan, 12.5 ±0.5 kJ·mol-1 for dehydroabietic acid and 14.4 ± 2.8 kJ·mol-1 for cis-pinonic acid, respectively. Different mixing states also had significant influence on the atmospheric stability of levoglucosan and dehydroabietic acid. When mixed with the inorganics, the reactivity of such tracers with OH showed different tendencies for different mixing approaches. When mixed with soot, the k2 of levoglucosan and dehydroabietic acid towards OH was significantly reduced compared to pure samples, indicating the mixed soot will lead to larger atmospheric stability of primary organic aerosol tracers.
    Using ATR-IR spectroscopy and GC-MS analysis, complemented by DFT calculation, the OH oxidation products for the tracers were detected, and ascribed to carboxylic acids or small molecular volatile organics for levoglucosan and polycarboxylic acids for cis-pinonic acid. Furthermore, by measuring the rate constant,the atmospheric lifetime of the tracers can be calculated. In this study, the atmospheric lifetime varied from 1.2 to 3.9 days for levoglucosan, 2.3 to 4.7 days for dehydroabietic acid and 2.1 to 3.3 days for cis-pinonic acid under different environmental conditions and different mixing states. As the longest lifetime of these tracers is still shorter than the residence time of aerosols in the troposphere, the concentration of the tracers measured in field measurements for source apportionment may be underestimated, thus lead to the negative error for source apportionment studies. The results obtained from this study are beneficial for understanding the fate of aerosols, and can also supply basic data for the improvement of existed source apportionment results.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/34334
Appears in Collections:大气污染控制中心_学位论文

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Recommended Citation:
赖承钺. 用于源解析的部分有机示踪物的大气稳定性研究[D]. 北京. 中国科学院研究生院. 2015.
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