A laser induced fluorescence instrument for measuring tropospheric NO2

Abstract

A new photolysis laser-induced fluorescence instrument for the detection of H 2 O and HDO in the lower stratosphere Rev. Sci. Instrum. 79, 064101 (2008); Nitrogen dioxide (NO 2 ), an essential gas in atmospheric chemistry, is almost always measured indirectly with just one technique: photolysis of NO 2 to NO, followed by detection of resulting NO. However, the photolysis introduces artifact signals that complicate the extraction of the NO 2 signal at low NO 2 volume mixing ratios. A new prototype instrument uses laser induced fluorescence to measure tropospheric NO 2 directly. The atmospheric fluorescence spectra measured with this instrument match the fluorescence spectra of NO 2 in a reference cell over the wavelength range 565.1-565.2 nm. This match indicates that fluorescence from other chemical species is not interfering with the measurements. The prototype's current detection limit is 280 parts per trillion ͑pptv͒ in 2.5 min with an absolute uncertainty of Ϯ15% ͑2 confidence͒. This detection limit, which can be improved with better optical filtering and more laser power, is currently adequate for urban air conditions.

Fluorescence Methods

“…Increased attenuation can be attained by use of multiple absorbing filters. The major drawback of absorbing filters is that the filters themselves fluoresce (Fong & Brune, 1997;Pfeiffer & Porter, 1964). Liquid filters (Anderson, 1976;Bradshaw et al, 1985;Fong & Brune, 1997) contain a concentrated chemical solution with a distinct absorption spectrum contained between two solid windows.…”

“…The major drawback of absorbing filters is that the filters themselves fluoresce (Fong & Brune, 1997;Pfeiffer & Porter, 1964). Liquid filters (Anderson, 1976;Bradshaw et al, 1985;Fong & Brune, 1997) contain a concentrated chemical solution with a distinct absorption spectrum contained between two solid windows. Interference filters exhibit high attenuation and high transmission and when coated with high grade quartz usually do not fluoresce; however, use of multiple filters does not lead to increased attenuation.…”

Mechanism of the NO2 Conversion to NO2− in an Alkaline Solution

“…On the other hand, several direct NO2 measurement methods have been developed, such as the luminol-NO2 chemiluminescence technique, 4,5 the UV-visible absorption spectroscopy, 6,7 the laser-induced fluorescence, and NO-O3 chemiluminesence with a photolytic converter. [8][9][10] In the luminol-NO2 chemiluminescence technique, luminol (5-amino-2,3-dihydro-1,4-phthalazine dione) produces intense chemiluminescence when it reacts with oxidizing agents in alkaline solution. Although this method is extraordinarily sensitive for determining NO2, ozone and sulfur dioxide, it also produces a strong luminescence which causes the positive interference with NO2 determination.…”

A New Method for Atmospheric Nitrogen Dioxide Measurements Using the Combination of a Stripping Coil and Fluorescence Detection

“…George and O'Brien 6 developed a fluorescence assay by a gas expansion (FAGE) instrument with a frequency-doubled Nd:YAG laser. Also, a tunable dye laser 7 was adopted to improve the sensitivity of nitrogen dioxide measurements. The laser technique is specific for nitrogen dioxide detection, in principle, because of selection of the excitation wavelength.…”