Influence of photolysis on multispectral photoacoustic measurement of nitrogen dioxide concentration

Figures & data

Figure 1. Experimental setup used by Harshbarger et al. (1973).

Figure 2. Comparison of the optical extinction and spectrophone (i.e., photoacoustic) spectra of NO₂ at 1333 Pa pressure (Harshbarger et al., 1973).

Figure 3. NO₂ gas calibration results at 405 nm from Lewis (2007).

Figure 4. Absorption cross-section spectrum of NO₂ at 294 K (Vandaele, 1998).

Figure 5. Schematic diagram of the photoacoustic instrument, including two lasers, chopper, photoacoustic resonator with microphone and piezoelectric transducer, two lock-in amplifiers, and personal computer (PC) (color figure available online).

Figure 6. NO₂ calibration of the photoacoustic instrument at 532 nm. For NO₂, the absorption coefficient is equal to the extinction coefficient. The measurement with the uncalibrated instrument (shown as gray solid line) is adjusted by multiplying with a constant, yielding the calibrated absorption coefficient, shown as gray dashed line.

Figure 7. Short-term measurement of the sample absorption coefficient at 532 nm with 405-nm laser on and off.

Figure 8. Photolysis of NO₂ caused by the 405-nm laser. The line shows the change of the sample absorption coefficient at 532 nm due to the photolysis of NO₂ caused by the 405-nm laser with 123 mW laser power. The difference between absorption coefficients and NO₂ concentrations with the 405-nm laser turned on and off is ∼11%.

Figure 9. Sample absorption coefficient at 532 nm with the 405-nm laser turned on and off followed by high-frequency modulation of the 405-nm laser power simulating operation conditions for multispectral photoacoustic instruments.

Figure 10. Change of sample light absorption coefficient measured at 405 nm. The difference between 405-nm absorption coefficients with the 532-nm laser turned on and off is ∼2%.

Figure 11. NO concentration change measured by the NO analyzer. Photolysis of NO₂ at 405 nm was sufficiently strong that the NO analyzer was saturated at its upper limit of 20,000 ppb by the NO produced.

Lewis , K. A. 2007 . “ Development of a dual-wavelength photoacoustic instrument for measurement of light absorption and scattering by aerosol and gases. Ph.D. dissertation ” . In Atmospheric Science Program, Department of Physics , Reno, Reno , NV : University of Nevada .

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Vandaele , A. C. , Hermans , C. , Simon , P. C. , Carleer , M. , Cloin , R. , Fally , S. , Mérienne , M. F. , Jenouvirier , A. and Coquart , B. 1998 . Measurements of the NO2 absorption cross-section from 42000 cm−1 to 10000 cm−1 (238–1000 nm) at 220 K and 294 K . J. Quant. Spectrosc. Radiat. Transfer , 59 : 171 – 184 . doi: 10.1016/S0022-4073(97)00168-4

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