Nitrate Radicals in Tropospheric Chemistry

Abstract

Abstract. Nitrate radicals are being recognized as key intermediates in a growing list of important chemical processes in the atmosphere. Here, the role of nitrate radicals (N0 3 ) in tropospheric chemistry is discussed, with special emphasis on results from field measurements, most of which have been made by differential optical absorption spectroscopy (DOAS), with matrix-isolation electron spin resonance being an alternative technique. Nitrate radicals were observed in the atmosphere at peak mixing ratios of 350 ppt. Long-term observation of N0 3 shows that 24-h averages in rural air masses are closer to a few ppt. Nevertheless, the NO, radical plays an important role in the non-photochemical conversion of NO to x HN0 3• Also, N0 3 is a strong oxidizing agent and initiates the night-time removal of atmospheric trace species such as olefins, aromatic hydrocarbons. and organic sulfur compounds. Finally, night-time peroxy radical production and release of reactive halogen species from sea salt aerosol might be initiated by N0 3 reactions.

Estimating N<sub>2</sub>O<sub>5</sub> uptake coefficients using ambient measurements of NO<sub>3</sub>, N<sub>2</sub>O<sub>5</sub>, ClNO<sub>2</sub> and particle-phase nitrate

“…The steady-state lifetimes can then be calculated from observations of the NO 3 and N 2 O 5 concentrations and the production term k 7 [NO 2 ][O 3 ], where k 7 is the rate constant for Reaction (R7). This method was first used by Platt and colleagues to assess the heterogeneous loss of N 2 O 5 (Platt and Heintz, 1994;Platt and Janssen, 1995;Heintz et al, 1996), and has been extended by Brown and colleagues to derive γ in regions far from NO x sources such as the marine environment (Aldener et al, 2006), aloft Brown et al, 2009) and most recently for the continental boundary layer (Brown et al, 2016a). [NO 2 ] and [O 3 ] measurements are required to calculate the rate of NO 3 production, which is generally assumed to be via Reaction (R7) only, although a contribution of NO 2 oxidation by stabilized Criegee intermediates has recently been hypothesized to represent a potential bias to this calculation (Sobanski et al, 2016).…”

Constraining the concentration of the hydroxyl radical in a stratocumulus-topped marine boundary layer from sea-to-air eddy covariance flux measurements of dimethylsulfide

“…Studies from Allan et al (2000) in the relatively clean MBL at Mace Head suggested that the nocturnal level of the nitrate radical hovers on the order of a pptv, with reaction with DMS being its most important loss mechanism. Platt and Heintz (1994) estimated a globally averaged concentration of 3 pptv for NO 3 .…”

Chlorine activation by N<sub>2</sub>O<sub>5</sub>: simultaneous, in situ detection of ClNO<sub>2</sub> and N<sub>2</sub>O<sub>5</sub> by chemical ionization mass spectrometry

“…The chemistry involves reactions of NO 3 with a suite of diverse volatile organic compounds (VOC), and heterogeneous reactions of both NO 3 and N 2 O 5 with aerosol particles ( Atkinson, 2000;Jacob, 2000;Mentel et al, 1996;Noxon et al, 1980;Platt and Heintz, Published by Copernicus Publications on behalf of the European Geosciences Union. 194 J. P. Kercher et al: Simultaneous, in situ detection of ClNO 2 and N 2 O 5 1994; Wayne et al, 1991).…”