High-Sensitivity Instrument for Measuring Atmospheric NO₂

Abstract

We report on the development of a high-sensitivity detection system for measuring atmospheric NO2 using a laser-induced fluorescence (LIF) technique around 440 nm. A tunable broad-band optical parametric oscillator laser pumped by the third harmonic of a Nd:YAG laser is used as a fluorescence excitation source. The laser wavelength is tuned at peak and bottom wavelengths around 440 nm alternatively, and the difference signal at the two wavelengths is used to extract the NO2 concentration. This procedure can give a good selectivity for NO2 and avoid interferences of fluorescent or particulate species other than NO2 in the sample air. The NO2 instrument developed has a sensitivity of 30 pptv in 10 s and S/N = 2. The practical performance of the detection system is tested in the suburban area for 24 h. The intercomparisons between the LIF instrument and a photofragmentation chemiluminescence (PF-CL) instrument have been performed under laboratory conditions. The correlation between the two instruments is measured up to 1000 pptv. A good linear relationship between the LIF measurements and the PF-CL measurements is obtained.

Intercomparison of measurements of NO<sub>2</sub> concentrations in the atmosphere simulation chamber SAPHIR during the NO3Comp campaign

“…Reduction of NO 2 to NO using a heated molybdenum catalyst or a photolytic converter followed by detecting the chemiluminescence of the reaction of NO with O 3 is the most common method (Kley and McFarland, 1980;Ryerson et al, 2000). Long path differential optical absorption (Platt et al, 1979), diode laser based absorption (Lenth and Gehrtz, 1985;Sonnenfroh and Allen, 1996;Li et al, 2004) and fluorescence (Thornton et al, 2000;Matsumoto et al, 2001;Matsumi et al, 2001;Dari-Salisburgo et al, 2009) spectroscopy are approaches to detect NO 2 directly. During the last decade cavity ring-down spectroscopy (CRDS) and its related forms cavity enhanced absorption spectroscopy (CEAS) and cavity attenuated phase shift spectroscopy (CAPS) have become powerful techniques to detect atmospheric trace gases (Ball and Jones, 2003;Brown, 2003) and have also been applied to NO 2 detection.…”

Fluorescence Methods

“…Comparisons of the LIF-based NO 2 instruments to PF-CL instruments have also been described by Matsumoto et al (2001) and by Matsumi et al (2001). The comparison of all data points NO 2 = 0-6 ppb described by Matsumoto et al in the marine boundary layer in Okinawa Island, Japan, showed agreement to within 2% with an R 2 of 0.99.…”

“…This spectral modulation is similar to the background measurement technique used by OH LIF instruments except that for NO 2 there is still appreciable fluorescence at the off-resonance frequency due to the continuum in the absorption spectrum. This technique has been applied in both the stratosphere (Perkins et al, 2001) and the troposphere (Cleary et al, 2002;Fong & Brune, 1997;Matsumoto and Kajii, 2003;Matsumi et al, 2001;Matsumoto et al, 2001;Thornton et al, 2000). In the instrument described in detail by Thornton et al (2000), the output from a narrow linewidth dye laser pumped by a 3 W, 8 kHz Nd:YAG laser excites a pair of overlapping rotational lines in the (430) A 2 B 2 ← 000 X 2 A 1 vibronic band of NO 2 at 17086 5 cm −1 (585.257 nm).…”

Estimation of photolysis frequencies from TOMS satellite measurements and routine meteorological observations

“…As a result, almost simultaneous actinic flux and global irradiance measurements are available at each wavelength from which the polynomials of the SIM method were calculated. The absorption cross section and quantum yield used for the J(O 1 D) calculations were those of Daumont et al (1992) and Matsumi et al (2001) respectively, while for the J(NO 2 ) calculation both functions used were from DeMore et al (1997). For the selection of the cloud free days we used the methodology described in Vasaras et al (2001), which is based on the variability of the measurements from a collocated pyranometer.…”