Field deployable laser sensor for calibration-free and real-time measurement of NOx from stationary sources

Nitrogen oxides (NOx) are common pollutants emitted from stationary sources, such as industrial boilers and power plants, with significant adverse impacts on the environment and biosphere. The abatement of NOx from anthropic industrial processes requires reliable and sensitive monitoring systems. To address this challenge, we report a sensitive, robust, and compact quantum cascade laser (QCL)-based sensor to measure NO and NO2 emissions from industrial exhausts. This sensor uses two quantum cascade lasers, which take advantage of the intense absorption spectra of NO at 1929 cm−1 and NO2 at 1599 cm−1. A high-temperature multipass cell is designed to withstand harsh environments, which increases the light path length. The NOx concentrations are directly determined from the wavelength modulation spectroscopic model without the need for calibration. We conducted several laboratory experiments to evaluate the sensor's performance, with a focus on accuracy, sensitivity and selectivity. In the end, we showcased the field deployment of our sensor by continuously measuring NOx concentrations in a 2.8-MW gas-fired industrial boiler.