Evaluation of adsorption effects on measurements of ammonia, acetic acid, and methanol
Evaluation of adsorption effects on measurements of ammonia, acetic acid, and methanol
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评估吸附对氨、乙酸和甲醇测量的影响
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
W. Hao
中科院分区：
文献类型：
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作者：
R. Yokelson;T. J. Christian;I. Bertschi;W. Hao
[1]我们研究了从进气口和单元中吸附和解吸气体如何影响闭合单元FTIR测量二氧化碳(CO2)、一氧化碳(CO)、甲烷(CH4)、一氧化氮(NO)、二氧化氮(NO2)、甲醇(CH3OH)、醋酸(CH3COOH)和氨(NH3)的准确性。当标准品通过不锈钢入口输送到池中时，观察到CH3OH和NH3的透过率暂时降低。然而，涂有卤化碳蜡的入口(通常用于系统)对CH3OH和NH3都有很好的透过性(与室温下的特氟龙相当)，即使在低至5°C的温度下也是如此。因此，这种蜡对于涂覆不能由特氟龙制成的采样系统部件很有价值。该仪器仅对NH3有延迟响应(∼10-40 S)，这归因于PYREX多程电池的钝化。为了确定烟雾呈现的复杂样本矩阵可能产生的采样伪影，将闭路FTIR系统与开放路径FTIR系统(不受采样伪影的影响)在混合良好的烟雾中进行了比较。NH3的类似电池钝化延迟是在此测试中发现的唯一人工制品。总体而言，结果表明，∼10 S足以检测我们的快速流动闭合电池系统采样的NH3/CO比值的80%。较长的采样时间或连续采样会产生更好的结果。在野外活动中，闭合细胞系统的采样时间通常是10到>；100 S，因此NH3可能被低估了5-15%。
[1] We examined how adsorption and desorption of gases from inlets and a cell could affect the accuracy of closed-cell FTIR measurements of carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), nitric oxide (NO), nitrogen dioxide (NO2), methanol (CH3OH), acetic acid (CH3COOH), and ammonia (NH3). When standards were delivered to the cell through a stainless steel inlet, temporarily reduced transmission was observed for CH3OH and NH3. However, a halocarbon wax coated inlet (normally used on the system) had excellent transmission (comparable to room temperature Teflon) for both CH3OH and NH3, even at temperatures as low as 5°C. Thus the wax is valuable for coating sampling system components that cannot be fashioned from Teflon. The instrument had a delayed response (∼10–40 s) for NH3 only, which was attributed to passivation of the Pyrex multipass cell. To determine sampling artifacts that could arise from the complex sample matrix presented by smoke, the closed-cell FTIR system was intercompared with an open-path FTIR system (which is immune to sampling artifacts) in well-mixed smoke. A similar cell passivation delay for NH3 was the only artifact found in this test. Overall, the results suggest that ∼10 s is sufficient to detect >80% of an NH3/CO ratio sampled by our fast-flow, closed-cell system. Longer sampling times or consecutive samples return better results. In field campaigns the closed-cell system sampling times were normally 10 to >100 s so NH3 was probably underestimated by 5–15%.