A thermal dissociation laser‐induced fluorescence instrument for in situ detection of NO₂, peroxy nitrates, alkyl nitrates, and HNO₃

TLDR

The authors present a new instrument that combines thermal dissociation with laser‑induced fluorescence to detect the total peroxy nitrates, alkyl/hydroxyalkyl nitrates, and HNO₃ in situ. The instrument operates by rapidly cooling and lowering the pressure after thermal dissociation to suppress interferences to 1–5%, and its performance is validated by laboratory tests and comparison with independent NOy measurements. It delivers routine, continuous measurements with 15% accuracy and detection limits of 90 ppt 10 s⁻¹ (S/N = 2) on a 1 ppb NO₂ background and 30 ppt 10 s⁻¹ on a 100 ppt NO₂ background, as confirmed by field observations at the UC Blodgett Forest Research Station.

Abstract

This paper describes a new instrument that uses a combination of thermal dissociation and laser‐induced fluorescence detection of NO 2 for in situ detection of the sum total peroxy nitrates, the sum total of alkyl nitrates and hydroxyalkyl nitrates, and HNO 3 . The instrument is capable of routine, continuous in situ measurements of these three classes of compounds that are accurate (15%) with a low detection limit (90 parts per trillion (ppt) 10 s −1 , S/N ratio = 2 on a background of 1 ppb NO 2 and 30 ppt 10 s −1 on a background of 100 ppt NO 2 ). Theoretical analysis of potential interferences combined with laboratory experiments that test for interferences show that rapidly cooling the gas and dropping the pressure after the thermal dissociation reduces interferences to the order of 1–5%. Observations in ambient air at the University of California Blodgett Forest Research Station demonstrate the capabilities of this instrument under field conditions. These field observations are compared with independent total NO y observations.