Two-photon formation of NH/ND(A 3Π) in the 193 nm photolysis of ammonia. II. Photolysis of NH2

Real-time monitoring of toxic components from fine dust air pollutant samples by utilizing spark-induced plasma spectroscopy

A growing modern-day concern is fine dust air pollution that contains heavy metals and ammonium ions (NH₄⁺) from industrial and agricultural waste sources, respectively. In the current study, the development of an innovative and effective technique for real-time, quantitative monitoring of toxic fine dust components using plasma emission spectroscopy is presented as a complement to emergency preparedness plans aimed at reducing dust pollution. A novel spark-induced plasma spectroscopic (SIPS) device that can control the frequency and magnitude of plasma was developed for the toxic pollutants in this work. SIPS utilizes an electrical discharge from a high voltage at a low current to produce plasma when the applied voltage is higher than the ambient voltage surrounding the electrodes. The detection limit of this setup was enhanced by a factor of 4.3 over laser-induced plasma spectroscopy (LIPS). This compact sensing device was used in combination with a new quantitative analytical method to measure the concentration of heavy metals and ammonia molecules in fine dust air pollution. By integrating the time-resolved plasma emission signals that were based on the plasma continuum decay time of each element, quantitative measurements of the minute changes in composition of 0.1 μg/m³ were conducted. The findings of this study could inspire future research on the use of SIPS for monitoring airborne fine dust pollutants with better sensitivity in real-time via a new quantitative analytical method.

Ammonia measurements with femtosecond laser-induced plasma spectroscopy

Femtosecond laser-induced plasma spectroscopy for in situ ammonia (NH₃) measurements was demonstrated in NH₃/N₂ mixtures. When a femtosecond laser at 800 nm was focused at the flow field, the parent NH₃ molecules would be photolyzed to generate electronics excited NH fragments, and then indirect measurements of NH₃ could be realized by detecting the NH fluorescence (A³Π-X³Σ^-) at 336 nm. A detection limit of 205 ppm was achieved. This work is the first attempt, to the best of our knowledge, for ammonia measurements with a femtosecond laser, and the results are useful for the development of ammonia diagnostics.

Ammonia detection and monitoring with photofragmentation fluorescence

Excimer laser fragmentation-fluorescence spectroscopy is an effective detection strategy for NH(3) in combustion exhausts at atmospheric pressure and high temperatures. Two-photon photofragmentation of NH(3) with 193-nm light yields emission from the NH(A-X) band at 336 nm. There are no major interferences in this spectral region, and the sensitivity is at the parts per billion (ppb) level. Quenching of the NH(A) state radical by the major combustion products is measured and does not limit the applicability of the detection method. Detection limits in practical situations are of the order of 100 ppb for a 100-shot (1-s) average. This technique could prove useful in monitoring ammonia emissions from catalytic and noncatalytic NO(x) reduction processes involving ammonia injection.