大气过氧乙酰基硝酸酯(PAN)自动化分析仪的研制与外场观测
文献类型：学位论文
| 作者 | 张根 |
| 学位类别 | 博士 |
| 答辩日期 | 2013-05 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 牟玉静 |
| 关键词 | 过氧乙酰基硝酸酯 过氧丙酰基硝酸酯 四氯化碳 配备电子捕获检测 器的气相色谱 大气 光氧化 Peroxyacetyl nitrate peroxypropionyl nitrate carbon tetrachloride gas chromatography-electron capture detector atmosphere photooxidation |
| 其他题名 | The development of automatic analyzer for atmospheric peroxyacetyl nitrate (PAN) and field measurements |
| 学位专业 | 环境科学 |
| 中文摘要 | 过氧乙酰基硝酸酯(PAN)是挥发性有机物(VOCs)和氮氧化物(NOx)在大气中通过光化学反应产生的二次产物，是光化学烟雾污染的一种重要的指示剂，同时它又可促进光化学氧化剂臭氧(O3)的形成。PAN 主要在近地面形成于人类活动密集的污染地区，而它一旦扩散到对流层上部，便可通过长距离传输至偏远地区，因此，PAN 是偏远地区氮氧化物重要的来源，并促进该地区O3 的光化学形成。 此外，PAN 对人眼具有刺激作用，且可诱发机体突变。与发达国家相比，我国在大气PAN 观测研究方面起步较晚，且仅少数研究组在我国个别地区开展了大气PAN 的短期观测。为此，本研究首先建立一套大气PAN、过氧丙酰基硝酸酯(PPN)和四氯化碳(CCl4)的可靠分析方法，并利用该方法对北京市大气PAN，PPN和CCl4 进行了一年多的观测；基于所建分析方法，利用国产气相色谱(SP3420A)等，实现了大气中PAN、PPN 和CCl4 的高灵敏度自动在线分析。本论文获得的主要研究成果如下： (1) 利用配备电子捕获监测器的气相色谱仪(HP5890)、六通阀及DB-1 毛细管色谱柱，建立了一套大气中PAN，PPN 和CCl4 的可靠分析方法。优化的色谱分析条件为：色谱柱温度为20oC、检测器温度为38oC、载气（氦气）的流速为8 mL min-1，补助气（高纯氮）的流速为54 mL min-1。该方法对PAN 的线性响应范围为0-15.8 ppbv，对PAN、PPN 和CCl4 的检测限(3 倍声噪比)分别为22、32和5 pptv，总不确定度分别为 ± 15%、± 15%和± 5%，分析频率为30 min。 (2) 获得了2010 年6 至9 月北京市大气中的PANs 浓度水平和变化特征，并分析了其来源和影响因素。PAN 和PPN(PANs)均呈现明显日变化特征，即早晚较低、午后出现峰值，表明它们为大气光化学二次产物；PAN 和PPN 相关性分析结果表明北京大气中PANs 主要来自人为源排放VOCs 的光氧化；观测期间PAN 和PPN 的平均值分别为2.61 ± 2.57 ppbv (N = 839)和0.52 ± 0.38 ppbv (N =152), 最大值分别为12.5 和2.16 ppbv；根据北京市大气中形成PAN 的主要前驱物观测浓度、它们与OH 反应速率常数及其光解速率常数，分别计算了乙醛、丙 酮、甲基丙烯醛、丁二酮、甲基丙醛酮和甲基乙烯基酮的过氧乙酰基自由基形成速率， 发现北京大气中PAN 主要来自乙醛的光氧化，占总前驱物贡献的71.2%；北京市大气PAN 的浓度与NO/NO2 比值呈负相关关系，计算结果表明热解消耗的PAN 在总生成的PAN 中所占比例均较大，显然，NO/NO2 比值和温度是影响北京大气PAN 浓度的关键因素；北京市大气中夜间PAN 的热解速率约为1 ppbv,折合OH 自由基的产率约为6.8 106 molecule cm-3 s-1，表明北京市夜间PAN 的热解是OH 自由基的一种重要来源，对北京市夜间大气化学具有重要影响。 (3) 获得了北京市2010-2011 年大气PAN、PPN 和CCl4 的平均日变化、月变化和季节变化特征。PAN 和PPN 的月平均浓度的低值均出现在中秋至早春，高值出现在夏季和早秋，其季节（或月）变化特征体现了光化学反应活性对大气PANs 形成的影响。CCl4 的季节（或月）变化规律与大气温度基本一致，表明北京市CCl4 主要来自溶剂的挥发；除冬季外，PAN 的平均日变化特征与O3 基本一致，即早晚低中下午高，表明二者均为光化学反应的二次产物。PAN 在冬季的日变化呈现为从早到晚逐渐增加趋势，而臭氧在下午交通高峰时段（约17:00）则出现明显下降，表明PAN 在寒冷冬季的热解速率很慢，微弱光化学产生的PAN可在大气中持续积累，而O3 则明显存在NO 的滴定消耗。全年CCl4 均无明显日变化特征，表明中下午相对高的扩散气流对CCl4 浓度的稀释作用可极大被CCl4 溶剂在相对较高气温下的快速挥发所抵消；北京市夏季PAN 与O3 线性相关分析的斜率(ΔO3/ΔPAN<18.0)明显低于发达国家城市，表明北京市存在更为严重的大气污染。 (4) 采用国产气相色谱(GC-ECD，SP3420-A)、气动十通阀切换技术、半导体制冷技术等，研制了一台PAN、PPN 和CCl4 的自动化在线分析仪，实现了三种污染物的高灵敏度和高频度在线分析。该色谱仪对PAN、PPN 和CCl4 的检测限分别为5、6 和3 pptv，相应的不确定度分别为1%、2%和2%，分析频率可低达5 min。 |
| 英文摘要 | Peroxyacetyl nitrate (PAN) is an important secondary pollutant formed via photochemical reactions of volatile organic compounds (VOCs) in the presence of nitrogen oxides (NOx), and it’s also an indicator for photochemical pollution in the atmosphere and contributes to the photochemical formation of O3. PAN is formed in the ground layer where this region is heavily polluted by human activity, diffused to the upper troposphere, and transported over long distances to the remote troposphere. Thus it acts as a crucial source of NOx in the remote troposphere where it may control the photochemical production of O3. In addition, PAN has been also recognized as mutagen and phytotoxin. Compared with developed countries, the researches associated with PAN were started later in China, and the short observations were conducted by limited groups in individual regions. Given this, a reliable method for atmospheric PAN, peroxypropionyl nitrate (PPN) and carbon tetrachloride (CCl4) was firstly developed in this study and applied to one-year measurements of these pollutants in Beijing. On the basis of the fisrtly developed method, an automatic detection method for these pollutants with high sensitivity was achieved by using domestic SP3420-A gas chromatograph. The main results were obtained in this study as follows: (1) A reliable detection method for atmospheric PAN, PPN, and CCl4 was developed by using HP-5890 gas chromatograph coupled with electron capture detector, six-port valve, and DB-1 capillary column. The optimized GC conditions were as follows: the GC oven and detrctor temperatures were maintained at 20 and 38°C, respectively; and the helium carrier gas and N2 make-up gas flow rates were adjusted to 8 and 54 mL min-1, respectively. Good linear correlation between the GC-ECD signals and PAN concentrations (0-15.8 ppbv) was observed. The detection limits (three times the signal to noise ratio) in this study were estimated to be 22 pptv for PAN, 36 pptv for PPN, and 5 pptv for CCl4, respectively, with the corresponding overall uncertainties of ± 15%, ± 15%, and 5%. The sampling frequency was set to 30 min. (2) The results of the measurements of atmospheric PAN and PPN during June-September 2010 demonstrated the levels of these pollutants and their diurnal variations, and the sources and effect factors for atmospheric PAN were also analyzed in this study. PAN and PPN (PANs) both exhibited distinct diurnal variations with maximum values in the afternoon and minimal values during early morning and midnight, and the correlation regression between them indicated anthropogenic VOCs dominanted the photochemical formation of PANs in Beijing. The mean and maximum values for PAN and PPN during the measuring period were 2.61 ± 2.57 ppbv (N = 839) and 12.5 ppbv, and 0.52 ± 0.38 ppbv (N = 152) and 2.16 ppbv, respectively. Atmospheric peroxyacetyl radical formation rates from acetaldehyde, acetone, methacrolein, biacetyl, methyl glyoxal, and methyl vinyl ketone are estimated by the concentrations of these species and OH radicals, the rate constants of their reactions with OH or photolysis, respectively. PAN was found to be mainly from the photooxidation of acetaldehyde accounting for 71.2% of the total contribution of these precursors in Beijing. Anti-correlation between PAN concentrations and the NO/NO2 ratios was found and the amount of PAN lost by thermal decomposition accounted for remarkable fractions of PAN produced from photochemical formation, both suggesting that air temperature and NO/NO2 ratio are the main influencing factors on atmospheric PAN concentration. The amount of thermal decomposition of PAN in Beijing was usually greater than 1 ppbv per hour after sunset, and hence OH formation rate from PAN thermal decomposition could be estimated to 6.8 106 molecule cm-3 s-1, which might be the main source of OH radical and have profound effect on the night chemistry in Beijing. (3) The results of one-year measurements of atmospheric PAN, PPN, and CCl4 during September 2010 to August 2011 demonstrated their average diurnal, monthly, and seasonal variations as follows: PAN and PPN both showed minimums in mid-autumn extended to early spring and maximum in summer and early autumn, and the seasonal (monthly) variation demonstrated the effect of photochemical reactivity on the formation of atmospheric PAN. CCl4 exhibited a similar seasonal (monthly) variation with temperature, indicating atmospheric CCl4 in Beijing was mainly from evaporation of solvents. Except the winter, the mean diunal variations of PAN and O3 both exhibited maximal values in the late afternoon and minimal values during early morning and midnight in other seasons, which implied they are both the products of photochemical reactions. The diurnal variation of PAN in winter exhibited a gradually increase from morning to night and O3 showed a maximum centered in the heavy traffic period (ca. 17:00), indicating the thermal decomposition rate of PAN was slow and it facilitated the accumulation of PAN formed through weak photochemical reactions, but for O3 it was greatly titrated by NO. For the whole year, CCl4 showed no distinct diurnal variations, implying that its fast diffusion in noontime or afternoon was greatly counteracted by its increasing evaporation rates from solvents under elevation of air temperature. Compared with developed countries, the relatively lower values of ΔO3/ΔPAN in summer implied that Beijing is suffering serious air pollution. (4) An automatic gas chromatograph for on-line measurement of atmospheric PAN, PPN, and CCl4 was developed by using SP3420-A gas chromatograph coupled with pneumatically ten-port valve and semiconductor refrigerator. This analyzer achieved the high sensitivity and frequency deteriminations of these three pollutants. The detection limits for PAN, PPN, and CCl4 were estimated to be 5, 6, and 3 pptv,and the corresponding overall uncertainties were estimated to be 1%, 2%, and 2%,respectively. The time resolution was as low as 5 min. |
| 公开日期 | 2014-10-20 |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/7698]  |
| 专题 | 生态环境研究中心_环境水质学国家重点实验室 |
| 推荐引用方式 GB/T 7714 | 张根. 大气过氧乙酰基硝酸酯(PAN)自动化分析仪的研制与外场观测[D]. 北京. 中国科学院研究生院. 2013. |
入库方式： OAI收割
来源：生态环境研究中心
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