Humidity and temperature corrections to improve accuracy of HF ambient air monitors based on tunable diode laser IR absorption measurements
View Patent ↗Method of determining a total HF concentration metric in an environment including measuring an uncorrected HF concentration metric in the environment based on a first infrared absorption measurement at a wavelength corresponding to a vibrational frequency of a non-hydrogen bonded gas phase HF molecule; determining an ambient H 2 O concentration metric in the environment available for reaction with the non-hydrogen bonded gas phase HF molecules at or about the time of obtaining the first infrared absorption measurement; calculating a HF hydrate concentration metric in the environment based on the uncorrected HF concentration metric, the ambient H 2 O concentration metric and a reaction equilibrium relationship between the non-hydrogen bonded gas phase HF molecule and the HF hydrate; and determining the total HF concentration metric in the environment based on the uncorrected HF concentration metric and an amount of HF determined by the HF hydrate concentration metric.
1. A method of determining a total HF concentration metric in an environment comprising:
(a) measuring an uncorrected HF concentration metric in the environment based on a first infrared absorption measurement at a wavelength corresponding to a vibrational frequency of a non-hydrogen bonded gas phase HF molecule;
(b) determining an ambient H 2 O concentration metric in the environment available for reaction with the non-hydrogen bonded gas phase HF molecules at or about the time of obtaining the first infrared absorption measurement;
(c) calculating a HF hydrate concentration metric in the environment based on the uncorrected HF concentration metric, the ambient H 2 O concentration metric and a reaction equilibrium relationship between the non-hydrogen bonded gas phase HF molecule and the HF hydrate; and
(d) determining the total HF concentration metric in the environment based on the uncorrected HF concentration metric and an amount of HF determined by the HF hydrate concentration metric.
2. The method of claim 1 , wherein the infrared absorption measurement is obtained via an apparatus that employs a tunable diode laser.
3. The method of claim 1 , wherein the ambient H 2 O concentration metric is determined based on the ambient temperature and a humidity metric selected from relative humidity and dew point, at or about the time of obtaining the first infrared absorption measurement.
4. The method of claim 1 , wherein the ambient H 2 O concentration metric is determined by measuring a second infrared absorption measurement at a wavelength corresponding to a vibrational frequency of an H—O bond within H 2 O molecules at or about the time of obtaining the first infrared absorption measurement.
5. The method of claim 1 , wherein the reaction equilibrium relationship between the gas phase HF molecule and the HF hydrate is based at least in part on the equilibrium constant, Keq(T), for the reaction H 2 O+HF HF.H 2 O at the ambient temperature.
6. The method of claim 5 , wherein the equilibrium constant, Keq(T), for the reaction H 2 O+HF HF.H 2 O at the ambient temperature is calculated based at least in part on thermodynamic parameters for the hydrogen bonding reaction associated with the HF hydrate at the ambient temperature.