DESIGN OF EXTRA CAVITY PHOTOACOUSTIC SPECTROMETER BASED ON BLUE DIODE LASER IN NO2 (NITROGEN DIOXIDE) GAS DETECTION

Background: NO2 detection is necessary because NO2 is an air pollutant causing photochemical smog and acid rain. In addition, respiratory diseases are caused by high levels of NO2 in the inhaled air. Aim: The purpose of this study was to detect NO2 using PAS utilizing Arduino Uno, an easy, simple, and low-cost research. Methods: The detection of Nitrogen Dioxide (NO2) gas with a Photoacoustic Spectrometer (PAS) using an Arduino Uno microcontroller has been carried out. The PAS system uses a blue diode laser with a wavelength of 450 nm as the radiation source because this wavelength is suitable for NO2 gas. The intensity of the laser beam is modulated using a modulation system with an on-off scheme using the Arduino Uno. The modulation frequency has been varied to get the maximum detection frequency. The photoacoustic cell used was a single resonator photoacoustic cell with type H. Sound sensor and photodiode were used in this measurement. The amplification of the signal was done by utilizing the Lock-in amplifier, and the constant time of Lock-in amplifier was also determined to optimize the PAS. Nitrogen gas was used to detect background signal. Results and Discussion: From the photoacoustic spectrometer optimization, the results obtained were a laser diode frequency of 1,000 Hz with a duty cycle of 50% and a Lock-in amplifier amplification of 10,000 times with a constant time of 3.3 ms. The maximum concentration reached in this measurement was 6 ppm. The background signal achieved in this measurement was 0.00002 V/W. The lowest detection limit achieved in this measurement was 0.0064 ppm.Conclusion: The gas sample containers containing NO2 with larger sizes tend to have a greater concentration. Sometimes, the NO2 concentration of the large sample gas container was overtaken by the small sample container.

CO2 Laser Photoacoustic Spectrometer for Measuring Acetone in the Breath of Lung Cancer Patients

A CO2 laser has the advantages of being high in power and having many laser lines in the 9–11 µm infrared region. Thus, a CO2 laser photoacoustic spectrometer (PAS) can have a multi-component measurement capability for many gas compounds that have non-zero absorption coefficients at the laser lines, and therefore can be applied for measuring several volatile organic compounds (VOCs) in the human breath. We have developed a CO2 laser PAS system for detecting acetone in the human breath. Although acetone has small absorption coefficients at the CO2 laser lines, our PAS system was able to obtain strong photoacoustic (PA) signals at several CO2 laser lines, with the strongest one being at the 10P20 line. Since at the 10P20 line, ethylene and ammonia also have significant absorption coefficients, these two gases have to be included in a multi-component measurement with acetone. We obtained the lowest detection limit of our system for the ethylene, acetone, and ammonia are 6 ppbv, 11 ppbv, and 31 ppbv, respectively. We applied our PAS system to measure these three VOCs in the breath of three groups of subjects, i.e., patients with lung cancer disease, patients with other lung diseases, and healthy volunteers.

Aerosol optical absorption and spectral dependence measurement with photoacoustic spectroscopy

<p>Light-absorbing carbonaceous aerosols mainly generated from the combustion of biomass and fossil fuels, play an important role in the global environment <sup>[1]</sup>. Multi-wavelength in-situ measurement of carbonaceous aerosol optical absorption is important both for reduce errors in assessing radiative forcing and component identification or source appointment of aerosols (such as biomass burning and diesel soot) with absorption Ångström exponent (AAE) <sup>[2]</sup>. A differential photoacoustic spectrometer (PAS) using a 438 nm laser diode was developed for simultaneously measure the aerosol optical absorption coefficient and the concentration of NO<sub>2</sub>. In order to evaluate the reliability of the differential photoacoustic spectrometer, we compared the NO<sub>2 </sub>concentration measured by PAS with the data from environmental monitoring station and showed good consistency. In the actual atmospheric measurement process, we observed a good correlation between the light absorption characteristics of aerosols and the concentration of NO<sub>2</sub> within a certain time range. In addition, a novel multi-wavelength photoacoustic spectrometer (MW-PAS) was developed to measure the aerosol optical absorption coefficients and its wavelength-dependent characteristics in the UV-VIS-NIR bands (405, 638, 808 nm). The performance of MW-PAS was evaluated by measuring the light absorption characteristics of kerosene soot aerosol. The measurement results are agreed with the results reported in literatures <sup>[3]</sup>.</p><p> </p><p>Reference</p><p>[1] J.G. Radney, R. You, M.R. Zachariah, C.D. Zangmeister, Direct in-situ mass specific absorption spectra of biomass burning particles generated from smoldering hard and softwoods. Environ. Sci. Technol. <strong>51</strong>, 5622-5629 (2017)</p><p>[2] T. Ajtai, N. Utry, M. Pintér, B. Major, G. Szabó, A method for segregating the optical absorption properties and the mass concentration of winter time urban aerosol. Atmos. Environ.<strong>122</strong>, 313-320 (2015)</p><p>[3] M. Gyawali, W.P. Arnott, R.A. Zaveri, C. Song, H. Moosmüller, L. Liu, M.I. Mishchenko, L.-W.A. Chen, M.C. Green, J.G. Watson, and J.C. Chow, Photoacoustic optical properties at UV, VIS, and near IR wavelengths for laboratory generated and winter time ambient urban aerosols. Atmos. Chem. Phys. <strong>12</strong>, 2587-2601 (2012)</p>