Detection of ammonia in near infrared region considering the effect of cross sensivity

Abstract

Ammonia gases have their own advantages and disadvantages; however it is important to monitar ammonia emission to avoid hazardous level. Ultraviolet or broadband Infrared absorption, and Photothermal Deflection prevent the speciesconversion, time delay, and adsorption problems associated with traditional sampling systems, but often use expensive, bulky or delicate radiation sources that are not suitable for commercialisation. In gas detection, cross sensitivity is one of the constraints since the air consists of a variety of gases. A few techniques were introduced such as using gas separation techniques or ratio calculation to overcome the problem. For ammonia gas sensing, it has been reported that the cross sensitivity with humidity is the main problem and this occurs in certain wavelength ranges. This is a strong indication that cross sensitivity for ammonia emission monitoring must be modelled. Choosing suitable wavelength of ammonia with minimal cross sensitivity effect can reduce the effect of cross sensitivity at infrared region. In this numerical prediction analysis, the optical transmission of ammonia was obtained through a model developed using a commercial simulator SpectralCalc-GATS, OptiSystem and Matlab. The developed model is then interfaced with the integrated sensor system model using OptiSystem for system performance and characterisation. The simulation shows that ammonia absorption cross section within 2200 nm to 2400 nm region has less cross sensitivity issues. It is not possible to discuss the cross sensitivity issue for every single atmospheric gas as there are too many gases in the atmosphere and the amount is small and subject to the surrounding environment. These simulations consider other gases such as CO2 and H2O Proper cross sensitivity is able to be simulated and characterised through the sensor model developed through this research.