High Sensitivity HNO3 Monitor using Continuous Wave Quantum Cascade Laser IR Absorption

HNO3 (nitric acid) is an important aerosol precursor that is coupled to the removal of natural and anthropogenic NOx from the atmosphere. Tropospheric HNO3 is both a terminal product from NO2 oxidation, and an important aerosol precursor. HNO3 is highly soluable and is extremely effective at increasing the cloud droplet number density. As a result, it has been implicated in the reduction of average cloud droplet size which increases cloud albedo. Furthermore it can decrease the likelihood of preciptitation which increases the effective cloud coverage. Because of its role in gas phase oxidation, fine aerosol formation and significant capacity to modify the cloud properties, direct sensitive and selective measurement technologies for nitric acid are crucially important. Direct measurements of HNO3 that are accurate, interference free, sensitive and rapid are needed to support particulate nitrate aerosol studies. The proposed instrument development to be undertaken in this project will produce a robust approach for measuring HNO3. The proposed instrument will be a major advancement over current commercial instrument capabilities, made possible by recent advances in technology using infrared quantum cascade lasers. This technology will yield a sensitive, selective measurement of this important aerosol precursor in dedicated measurement campaigns and at remote clean air monitoring stations. Commercial Applications and Other Benefits: The proposed instrument will provide the capability to measure atmospheric abundances of HNO3 in real time in order to better assess nitrogen oxide chemistry resulting in tropospheric ozone production and subsequent aerosol and cloud modifications. Improved understanding of aerosol and cloud properties will improve our understanding of global climate change and help evaluate mitigation strategies. There is a worldwide market for such measurement systems in the environmental and aerosol research communities.