Open-path deep-ultraviolet absorption spectroscopy for ammonia measurements in animal enclosures

Ammonia (NH₃) is the most abundant alkaline gas in the atmosphere and plays a significant role in secondary aerosol formation and nitrogen cycling, influencing regional air quality and ecosystem nitrogen deposition. Agricultural activities are the dominant sources of atmospheric NH₃. However, accurate quantification of NH₃ emissions from animal enclosures remains challenging owing to the high humidity, elevated particulate loading, and wide range of NH₃ concentrations in these settings.

In this study, we present an open-path deep-ultraviolet optical absorption spectroscopy system for in situ NH₃ measurements. The instrument measures absorption spectra from 199 to 213 nm, a region in which NH₃ exhibits intense and highly structured absorption features that enable selective and sensitive detection. The entire system is powered by a portable power bank bundle and can operate continuously for over 6 hours. Laboratory characterization experiments demonstrate a detection limit of 74 ppb at a 1 s integration time with an optical path length of 50 cm. Chamber experiments show that the instrument has an excellent dynamic range, exhibiting a robust and linear response to NH₃ from 0.1 to 100 ppm. We demonstrate the application of an early-prototype to monitoring and mapping NH₃ in and around animal enclosures. The technique offers new opportunities for improving NH₃ monitoring in animal housing and supports the development of mitigation strategies for agricultural air quality management.