Accuracy and sensitivity of NH ₃ measurements using the Dräger Tube method

Abstract. Regional estimates of ammonia (NH3) emissions are often missing data from heterogeneous or small fields. Areas with no experienced staff or in-field power supply also prevent the use of accurate and fully established micrometeorological measurement techniques. The Dräger Tube method (DTM) is a calibrated open and dynamic chamber method, which requires little training to use and is relatively inexpensive. It uses NH3 detector tubes (Dräger Tubes), an automatic pump, and a chamber system comprised of four stainless-steel chambers connected with PTFE tubing. Even though the DTM is often used in countries such as Germany and China, the detection accuracy, precision and sensitivity have not been tested yet. In order to quantify those for the DTM, we simultaneously measured defined NH3 mixing ratios with the Dräger Tubes, with quantum cascade laser spectroscopy (QCLS) (MGA7, MIRO Analytical AG, Switzerland) and with cavity ring-down spectroscopy (G2103, Picarro, Inc., USA). Second, we tested the effects of exchanging the tubing material and heating the tubing under laboratory conditions, as well as PTFE film attachments or wiping of the DTM chamber system with ethanol during outdoor measurements, on performance improvements. Results showed that the Dräger Tubes had a detection limit between 150 and 200 ppb, which is 3 to 4 times higher than originally assumed. Dräger Tube concentration measurements also underestimated NH3 concentrations by 43 % to 100 % for mixing ratios between 50 and 300 ppb and by 28 % to 46 % for mixing ratios between 500 and 1500 ppb. The PTFE tubing material showed similar performance to the polyester–polyurethane tubing material regarding response time, which was further improved by heating the tubing to 50 °C. The modifications to the chamber surface and cleaning in the outdoor experiment did not lead to any improvements to the NH3 concentration measurements. The results suggest that the DTM should only be used where alternatives are unfeasible and high NH3 emissions are to be expected. Further assessment of calibrated DTM using reference methods is required for a comprehensive evaluation, and alternative developments for a more appropriate method replacing the DTM in small-plot applications is encouraged.