In this review, applications of near-infrared photoacoustic spectroscopy are presented as an opportunity to evaluate human respiration because the measurement of breath is fast, intact and simple to implement. Recently, analytical methods for measuring biomarkers in exhaled air have been extensively developed. With laser-based photoacoustic spectroscopy, volatile organic compounds can be identified with high sensitivity, at a high rate, and with very good selectivity. The literature review has shown the applicability of near-infrared photoacoustic spectroscopy to one of the problems of the real world, i.e., human health. In addition, the review will consider and explore different breath sampling methods for human respiration analysis.

Photoacoustic spectroscopy represents a powerful technique for measuring extremely low absorptions independent of the path length and offers a degree of parameter control that cannot be attained by other methods. We report precise measurements of the ammonia absorption coefficients at the CO₂ laser wavelengths by using a photoacoustic (PA) cell in an extracavity configuration and we compare our results with other values reported in the literature. Ammonia presents a clear fingerprint spectrum and high absorption strengths in the CO₂ wavelengths region. Because more than 250 molecular gases of environmental concern for atmospheric, industrial, medical, military, and scientific spheres exhibit strong absorption bands in the region 9.2–10.8 μm, we have chosen a frequency tunable CO₂ laser. In the present work, ammonia absorption coefficients were measured at both branches of the CO₂ laser lines by using a calibrated mixture of 10 ppm NH₃ in N₂. We found the maximum absorption in the 9 μm region, at 9R(30) line of the CO₂ laser. One of the applications based on the ammonia absorption coefficients is used to measure the ammonia levels in exhaled human breath. This can be used to determine the exact time necessary at every session for an optimal degree of dialysis at patients with end-stage renal disease.

Ethylene is a classical plant hormone and has appeared as a strong molecule managing many physiological and morphological reactions during the life of a plant. With laser-based photoacoustic spectroscopy, ethylene can be identified with high sensitivity, at a high rate and with very good selectivity. This research presents the dynamics of trace gases molecules for ethylene released by cherry flowers, apple flowers and strawberry flowers. The responses of distinctive organs to ethylene may fluctuate, depending on tissue sensitivity and the phase of plant development. From the determinations of this study, the ethylene molecules at the flowers in the nitrogen flow were established in lower concentrations when the value is correlated to the ethylene molecules at the flowers in synthetic air flow.

The hypothesis that blood, urine and other body fluids and tissues can be sampled and analyzed to produce clinical information for disease diagnosis or therapy monitoring is the basis of modern clinical diagnosis and medical practice. The analysis of breath air has major advantages because it is a non-invasive method, represents minimal risk to personnel collecting the samples and can be often sampled. Breath air samples from the human subjects were collected using aluminized bags from QuinTron and analyzed using the laser photoacoustic spectroscopy (LPAS) technique. LPAS is used to detect traces of ethylene in breath air resulting from lipid peroxidation in lung epithelium following the radiotherapy and also traces of ammonia from patients subjected to hemodialysis for treatment of renal failure. In the case of patients affected by cancer and treated by external radiotherapy, all measurements were done at 10P(14) CO₂ laser line, where the ethylene absorption coefficient has the largest value (30.4 cm⁻¹ atm⁻¹), whereas for patients affected by renal failure and treated by standard dialysis, all measurements were performed at 9R(30) CO₂ laser line, where the ammonia absorption coefficient has the maximum value of 57 cm⁻¹ atm⁻¹. The levels of ethylene and ammonia in exhaled air, from patients with cancer and renal failure, respectively, were measured and compared with breath air contents from healthy humans. Human gas biomarkers were measured at sub-ppb (parts per billion) concentration sensitivities. It has been demonstrated that LPAS technique will play an important role in the future of exhaled breath air analysis. The key attributes of this technique are sensitivity, selectivity, fast and real time response, as well as its simplicity.

Measuring ammonia from the environmental air is a sensitive and prioritized issue due to its harmful effects on humans, ecosystems, and climate. Ammonia is an environmental pollutant that has an important role in forming secondary inorganic aerosols, the main component of fine particulate matter concentrations in the urban atmosphere. Through this study, we present a gas analyzer that utilizes the technique of laser photoacoustic spectroscopy to measure ammonia concentration in three different sites located in Magurele, (44°20′58″ N 26°01′47″ E, 93 m altitude), Romania, from March to August 2021 at the breathing level of 1.5 m above ground. The ammonia concentrations from the ambient air were elevated in summer (mean of 46.03 ± 8.05 ppb (parts per billion)) compared to those measured in spring (18.62 ± 2.92 ppb), which means that atmospheric temperature affects ammonia concentrations. The highest mean ammonia concentrations occurred in August, with an ammonia concentration level of 100.68 ± 11.12 ppb, and the low mean ammonia concentrations occurred in March, with an ammonia level concentration of 0.161 ± 0.03 ppb. The results confirm that meteorological characteristics (i.e., temperature) and motor vehicles are major contributors to the elevated ammonia levels during the monitoring period.