基于化学富集法的大气气态氨在线测量技术研究

As the only alkaline gas in the atmosphere, ammonia is an important precursor of secondary aerosol formation and it inhibits the formation of acid rain. Due to the particularity of the domestic complex atmospheric pollution, the domestic emphasis on ambient ammonia measurement is far behind the abroad, where many techniques development have already been in application. Due to the specialty of ammonia, most of the instruments can not measure accurately at the low concentration. Therefore, it is necessary to develop new measurement technique of independent intellectual property rights, which is conducive to promote the progress of atmospheric sciences of China..Presently, the common measurement of ammonia can be divided into optical and chemical methods. The optical method is characterized by high time resolution, but expensive and narrow range of applications, while the chemical method is of high accuracy and cheap, but of the low time resolution. In this study, a way of chemical enrichment is introduced into the online measurement of ammonia to improve its time resolution. Based on new method, we will construct an online ammonia measurement system which will be tested by the varied conditions to quantify its performance. Field campaigns are planned to be held for the inter-comparisons of the new system with other relevant ammonia measurement instruments to assess the reliability and obtain feedbacks for further improvement of the system. The results of this study can contribute to the formulation of ammonia emission inventory, find out the distribution of ammonia emission in China and ammonia contribution to acid rain and secondary aerosol formation, and provide basic data for the in-depth research of pollution forecasting models.

作为大气中唯一的碱性气体，氨是二次气溶胶的生成的主要前体物，抑制酸雨的生成。国际上对气态氨的研究重视程度远高于国内，在测氨技术开发及应用上更是遥遥领先。由于氨自身的特性，大多仪器对低浓度氨的测量精度不高。因此，有必要开发新型的在线测量方法，同时积极发展自主知识产权的测量技术有利于推动我国大气环境事业的进步。.目前，常见的测氨法可分为光学法和化学法，光学法的特点是时间分辨率高，但价格昂贵，应用范围窄；化学法精度高、便宜，但时间分辨率低。本研究采用化学富集的方法，在确保测量精度的前提下，富集气态氨，提高测量时间分辨率。以此方法为基础，组建气态氨的在线测量系统，对系统进行条件测验，量化其性能指标，应用于外场观测进行验证，不断完善测量系统。本研究的成果有助于氨排放清单的制定，了解我国氨排放的分布及氨对酸雨和二次气溶胶形成的贡献，为后续研究及污染预报模式提供基础数据。

氨是大气中的重要碱性气体和含氮沉降化合物，不仅在高浓度时可直接危害生态系统，也可以参与形成细粒子影响大气能见度及降水pH。沉降后，可导致水体富营养化、土壤酸碱失衡，反应生成温室气体或促进温室气体的释放，进而影响气候。国际上对气态氨的研究重视程度远高于国内，在测氨技术开发及应用上更是遥遥领先。由于氨自身的特性，大多仪器对低浓度氨的测量精度不高。因此，有必要开发新型的在线测量方法，同时积极发展自主知识产权的测量技术有利于推动我国大气环境事业的进步。.本研究分析现有各种大气氨测量技术的优劣后，自主开发了运用化学富集技术测量大气气态氨的方法，并依据该方法成功研制出原理样机系统。该方法对大气氨的选择性唯一，测量时间分辨率较高，经实验室测试和外场观测验证，该方法可行性很好。这套系统包括气相氨吸收转化为液相铵、液相铵在强碱条件下吹扫至气相和气态氨催化氧化为氮氧化物三个部分，大气中氨经过前两个部分的处理后得到富集与提纯，可以大幅度提高氨检测准确性、降低检测限。本研究对各部分关键部件扩散捕集分离管、氨转化模块以及氨催化氧化炉，进行了设计、加工，并设计试验对其进行测试，结果显示，系统对大气氨的捕集效率在97%以上；当采样流量为10L/min时，氨富集倍数可达4倍，系统检测限为0.07微克/立方米。