Abstract
The concentration of trace gases in the atmospheric environment is extremely low, but it has a great impact on the living environment of organisms. Photoacoustic spectroscopy has attracted extensive attention in the field of trace gas detection because of its high sensitivity, good selectivity, and fast response. As the core of a photoacoustic detection setup, the photoacoustic cell has a significant impact on detection performance. To improve detection sensitivity, a sphere-tube coupled photoacoustic cell (STPAC) was developed, which was mainly composed of a diffuse-reflective sphere and an acoustic resonance tube. Modulated light was reflected multiple times in the sphere to increase optical path, and photoacoustic (PA) signals were further amplified by the tube. Based on STPAC, a PA gas detection setup was built with a laser diode (LD) at 450 nm as the light source. The experimental results showed that the minimum detection limit (noise equivalent concentration, NEC) of NO2 was ~0.7 parts per billion (ppb). Compared with the T-type PA cell (TPAC) in which the modulated light passed through the sphere, the signal-to-noise ratio of STPAC was increased by an order of magnitude at the same concentration of the NO2 sample.
Highlights
Nitrogen dioxide (NO2 ) is a trace gas toxic to living beings, which is mainly discharged into the atmosphere by combustion and other processes [1,2]
A PA gas detection setup was built to verify the performance of sphere-tube coupled photoacoustic cell (STPAC)
An integrating sphere used as the absorption cell, and the modulated light reflected multiple times to increase was used as the absorption cell, and the modulated light reflected multiple times to the optical path
Summary
Nitrogen dioxide (NO2 ) is a trace gas toxic to living beings, which is mainly discharged into the atmosphere by combustion and other processes [1,2]. The average concentration of NO2 in the atmosphere is usually 5–30 ppb, but the concentration is several orders of magnitude higher near the NO2 release source [3]. NO2 has a strong absorption line in the visible region, and absorption intensity is the largest in the blue-violet range [5,6]. When the wavelength is lower than 415 nm, NO2 undergoes photolysis [7,8]. With the development of laser diode (LD) manufacturing technology, a low-cost blue LD with a central wavelength of 450 nm has become a suitable light source for the detection of NO2 by absorption spectroscopy
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