大气环境科学实验室知识库

      植物源挥发性有机物(BVOCs)是植物释放的一类挥发性有机物，其对臭氧和二次有机气溶胶 的生成 具有显著贡献。臭氧是一种典型的植物毒素，可影响植物正常的生理生长过程， 进而 影响植物 BVOCs的排放，因此在区域性臭氧污染严重且有上升趋势的当下，研究臭氧浓度变化对植物 与大气间 BVOCs交换 的影响 ，尤其是 在 研究 BVOCs中 占比超过 50%的异戊二烯在不同臭氧浓度条件下的排放情况， 具有 重要的现实意义和 科学 意义。 开顶式气室是一种广泛用于研究植物对 气体浓度 变化响应的实验装置，但以往的设计 主要用于农作物， 在 用于研究臭氧浓度变化对生长迅速的加杨与大气间 BVOCs交换时 存在无法调节高度、与外界环境差异 较大 等问题。 另外， 课题组已有的 分辨率为 1h的 在线 VOCs分析仪 难以 满足 野外 BVOCs多 个 开顶式气室 的 同步采样 的分析
需求 。 因此 本 研究 研制 了一套 可用于木本植物的 以 开顶 式气室为主的 熏蒸系统 ，建立了 一套 BVOCs的离线采样和分析方法，并进行了 不同臭氧浓度条件下 加杨 排放 异戊二烯的 熏蒸实验，获得了以下主要研究成果：
      1、 研制 了 一套 以 开顶式 气室为主的 熏蒸系统 该系统主要 由 空气净化装置、 O3发生装置、风机、管道、室壁和框架 等 组成 。
      2、对 开顶式 气室进行了 性能 评价 ：在室外气温 27.5℃时，气室内部 不同位置 温差小于 0.5 气室内外温差最大 2.8 气室内部的湿度差异最高为 3.0%左右，内外湿度差最高 6.0%；气室内部臭氧浓度分布均匀 当室内臭氧浓度为150.0 ppbv左右时， 不同高度处臭氧浓度差异保持在 5.0 ppbv以内 臭氧发生器工作性能稳定，能够保持气室内外 70.0 3.0 ppbv的浓度差 臭氧催化剂去除效果明显，低浓度场气室内臭氧浓度基本保持在 10.0 ppbv以下 。
      3、改进了 课题组原有 的 自动在线 VOCs分析仪，建立了一套稳定可靠且适合野外采样的 BVOCs离线采样和分析方法 。该方法 通过 低温 吸附管采集BVOCs样品， 带回实验室后 采用高温热解析 200 的方法， 在高纯氮气保护下 将 所采 样品吹入 VOC分析仪 的超低温富集管（ （-100 进行定量分析。 对比在线分析和离线分析结果 ，发现 离线方法 对 BVOCs中的 主要 物种异戊二烯的捕获效率为 95%。
      4、 利用 所研制的 OTCs臭氧熏蒸系统研究了 不同臭氧浓度 D室： O3浓度10.0 ppbv左右； E室： O3浓度为 环境浓度； A室：环境浓度 + O3浓度 80.0 ppbv 对加杨排放异戊二烯的影响 ，发现不同臭氧浓度条件下加杨排放的异戊二烯浓度 具有 明显差异， 同一时间 D室和 A室中的异戊二烯浓度差可达 10.0 ppbv以上，即 随着臭氧浓度的升高 加杨 排放异戊二烯浓度 明显 降低 。

      Biogenic volatile compounds (BVOCs) are a kind of volatile organic compounds released to atmospheric by plants during their growth process, which contribute significantly to the formation of ozone and secondary organic aerosols. As a typical plant phytotoxin, ozone can affect the normal physiological growth process of plants and even affect the emission of BVOCs. It is of great practical and scientific significance to study the effect of ozone concentration to the exchange of BVOCs between plants and the atmosphere, especially the emission of isoprene, which accounts for more than 40% of BVOCs, when the regional ozone pollution is serious and rising. Open-top chamber is a kind of experimental device widely used to study the response of plants to climate change. However, previous designs were mainly used for crops. There are some problems such as the inability to adjust height and the great difference with the external environment when used to study the exchange of BVOCs between populus canadensis and the atmosphere when ozone concentration changes rapidly. In addition, the commonly used on-line instruments (such as VOCs analyzer with resolution of 1 h) can not meet the requirement of simultaneous sampling of multiple open-top BVOCs in the field. Therefore, an open-top air chamber fumigation system for woody plants has been developed. An off-line sampling and analysis method for BVOCs has been established. Fumigation experiments of populus canadensis isoprene emissions under different ozone concentrations have been carried out. The following main research results have been obtained:
      1. A suit of fumigation system with open-top chamber was developed. The system consists of air purification device, catalytic device, test gas generator, fan, pipe line, chamber wall and frame, etc.
      2. The performance evaluation of open-top air chamber is carried out: when the outdoor temperature is up to 27.5 ℃℃, the temperature difference inside the air chamber is less than 0.5 ℃℃; the temperature difference inside and outside the air chamber is up to 2.8 ℃℃; the humidity difference inside the air chamber is about 3.0%, and the humidity difference inside and outside the air chamber is up to 6.0%; the ozone concentration distribution inside the air chamber is uniform, and the difference of ozone concentration at different altitudes is kept within 5.0 ppbv; the performance of the ozone generator is stable, it can maintain the concentration difference of 70.0 + 3.0 ppbv inside and outside the gas chamber; the removal effect of specific ozone catalyst is obvious, and the concentration of ozone in the gas chamber of low concentration field is basically kept below 10.0 ppbv.
      3. Improve the original automatic online VOCs analyzer of our research group, and establish a stable and reliable off-line sampling and analysis method of BVOCs suitable for field sampling. This method collects BVOCs samples by cryogenic adsorption tube and brings them back to the laboratory. The samples are analyzed quantitatively by high temperature thermal analysis (200 ℃℃) under the protection of high purity nitrogen and injected into the cryogenic enrichment tube of BVOC analyzer (-100 ℃℃). Compared with on-line analysis and off-line analysis, we found that the off-line capture efficiency of isoprene, the main species in BVOCs, was 95%.
     4. The effects of different ozone concentration (room D: about 20.0 ppbv; room E: ambient concentration; room A: ambient concentration + 80.0 ppbv) on isoprene emission from Populus canadensis were studied by using the developed OTCs ozone fumigation system. It was found that the concentration of isoprene emitted from Populus canadensis under different ozone concentration was significantly different, and the difference of isoprene concentration between room D and room A at the same time could be more than 10.0 ppbv. That is, with the increase of ozone concentration, the concentration of isoprene emission from poplar decreased significantly.