Department of Biosystems Engineering, University of Aarhus, Faculty of Agricultural Sciences, Blichers Alle 20, DK-8830 Tjele, Denmark.
Sensors (Basel). 2010;10(5):4634-42. doi: 10.3390/s100504634. Epub 2010 May 4.
Correct measurements of ammonia concentration in air still present considerable challenges. The high water solubility and polarity can cause it to adsorb on surfaces in the entire sampling system, including sampling lines, filters, valves, pumps and instruments, causing substantial measuring errors and time delays. To estimate time delay characteristics of a Photo Acoustic Multi Gas Monitor 1312 and a Multi Point Sampler continuous measurement of aerial ammonia concentrations at different levels was performed. In order to obtain reproducible data, a wind tunnel was used to generate selected concentrations inside and a background concentration representing the air inlet of the tunnel. Four different concentration levels (0.8 ppm, 6.2 ppm, 9.7 ppm and 13.7 ppm) were used in the experiments, with an additional outdoor concentration level as background. The results indicated a substantial time delay when switching between the measuring positions with high and low concentration and vice versa. These properties may course serious errors for estimation of e.g. gas emissions whenever more than one measuring channel is applied. To reduce the measurement errors, some suggestions regarding design of the measurement setup and measuring strategies were presented.
空气中氨浓度的准确测量仍然存在相当大的挑战。高水溶性和极性会导致其在整个采样系统的表面上吸附，包括采样线、过滤器、阀门、泵和仪器，从而导致大量的测量误差和时间延迟。为了估计 Photo Acoustic Multi Gas Monitor 1312 的时间延迟特性，对不同水平的空气中氨浓度进行了多点连续测量。为了获得可重复的数据，使用风洞在内部和代表隧道进气口的背景浓度下产生选定的浓度。在实验中使用了四个不同的浓度水平（0.8ppm、6.2ppm、9.7ppm 和 13.7ppm），外加一个户外浓度水平作为背景。结果表明，在高浓度和低浓度测量位置之间切换时存在较大的时间延迟，反之亦然。这些特性可能会导致在应用多个测量通道时，例如对气体排放的估计产生严重误差。为了减少测量误差，提出了一些关于测量设置和测量策略设计的建议。
