Flight Instrument We have developed a time-gated laser-induced fluorescence (LIF) instrument capable of making accurate (5%, 1s), continuous, autonomous, in situ observations of NO2 with the sensitivity (15 ppt/10 sec at S/N = 2) and portability necessary to study NO2 anywhere in the troposphere. This technique is advantageous because it is spectroscopically specific and direct in that it does not require conversion of NO2 into another species (e.g. NO) prior to detection, eliminating a class of potential interferences. The current version of this instrument has operated on the C-130, DC-8 and autonomously at various ground stations around the United States.

Ultralight LIF Instrument We have designed, constructed and field tested a relatively inexpensive, autonomous and lightweight instrument capable of making accurate (5%, 1s), continuous, autonomous, in situ observations of NO2 with the sensitivity (150 ppt/min at S/N = 2). The instrument couples a commercial cw external-cavity tunable diode laser (640nm) with a continuous supersonic expansion. The total package is completely automated, and has a modest size of 0.5 m3 and 118 kg. Recent advancements in diode laser technology have allowed us to blue-shift our excitation wavelength to 408nm, significantly increasing our sensitivity. This instrument has operated at Granite Bay, CA and at Chebogue Pt, NS.

Cleary, P.A. et al., Laser-induced Fluorescence Detection of Atmospheric NO2 Using a Commercial Diode Laser and a Supersonic Expansion, Applied Optics, 41(33) 6950-6956, 2002. Article (pdf)

Thornton, J.A., Atmospheric NO2: In Situ Laser-Induced Fluorescence Detection at Parts per Trillion Mixing Ratios, Analytical Chemistry, 72, 528 (2000). Article (pdf)

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Thermal Dissociation - Laser Induced Fluorescence

We have developed an instrument designed to make in situ observations of the major NOy reservoirs. Thermal dissociation (TD) is used to fragment labile NOy species into NO2 and a companion radical. The NO2 fragment is then detected via LIF. The TD section is a second channael operating in parallel detecting ambient NO2. In the TD channel, ambient air flows rapidly (15ms residence time) through a quartz tube heated by a nichrome wire. NOy species that fragment to NO2 are then detected via LIF. Calculations and laboratory experiments show the instrument can easily distinguish between signals due to peroxynitrates (RO2NO2), alkyl and hydroxyalkyl nitrates (RONO2) and HNO3 by varying the temperature in the dissociation region.

D.A. Day, P.J. Wooldridge, M. Dillon, J.A. Thornton, R.C. Cohen, A Thermal dissociation-laser induced fluorescence instrument for in-situ detection of NO2, peroxy(acyl)nitrates, alkyl nitrates, and HNO3., J. Geophys. Res., 107(D6), 10.1029/2001JD000779, 2002. Article (pdf)

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We have designed, constructed and field tested a relatively inexpensive, autonomous and lightweight instrument capable of making accurate (8 %), continuous, in situ observations of NO3, N2O5 with a sensitivity of 16 ppt/ min at S/N=2. NO3 is detected using a pulsed diode laser at 662 nm combined with time gated fluorescence detection. N2O5 is thermally decomposed to NO3 in a heated inlet and detected as the sum of NO3 and N2O5. This instrument has operated in East of the San Francisco bay, in Mexico City, and at the Blodgett Forest Research Station, CA.

E.C. Wood, P.J. Wooldridge, T. Albrecht, J. Frees and R.C. Cohen, A prototype for in situ detection of atmospheric NO3 and N2O5 via Laser Induced Fluorescence, Env. Sci. and Tech. (37) 5732-5738, 2003. Article (pdf)

E.C. Wood, T.H. Bertram, P.J. Wooldridge and R.C. Cohen, Measurements of N2O5, NO2 and O3 East of the San Francisco Bay, Atmos. Chem. Phys. Disc. 4 6645-6665 2004. Atmos. Chem. Phys. (5) 483-491, 2005. Article (pdf)

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