Development and validation of a laser-absorption-based method for in-situ and high-precision water vapor dew point temperature measurement

Abstract

Dew point temperature is an important gas state parameter. Accurately measuring dew point temperature is a challenge because it is not only related to gas concentration, but also gas temperature and pressure. We proposed a dew point temperature measurement method based on tunable diode laser absorption spectroscopy (TDLAS), in which water vapor temperature, pressure and concentration can be measured simultaneously with a single near-infrared laser source. Two H2O absorption lines near 1381 nm (7242.37 cm−1 and 7243.08 cm−1) were selected, and their coefficients of temperature-dependence of the self-broadened half-width were measured experimentally to improve the HITRAN databases. The wavelength shift of the laser was suppressed by a temperature compensation circuit. To confirm the capability of this method, a series of experiments were performed in a standard temperature and humidity chamber through the target absorption lines. In the whole dew point range of the experiment, the maximum deviation between the measurement results of our method and the high precision chilled mirror hygrometer is less than 0.9 ℃. According to the time-series measurements of atmospheric H2O, the measurement accuracy of 0.57% and the detection limit of −61.1 ℃ were verified under the condition that the optical path was only 10.5 cm. This result shows the potential of this method in low-cost, calibration-free, in-situ and high-precision dew point measurement.