The photolysis of ortho-nitrophenols: a new gas phase source of HONO

Abstract

Formation of nitrous acid (HONO) in the gas phase has been observed for the first time in a flow tube photoreactor upon irradiation (l = 300-500 nm) of 2-nitrophenol and methyl substituted derivatives using a selective and sensitive instrument (LOPAP) for the detection of HONO. Formation of HONO by heterogeneous NO 2 photochemistry has been excluded, since production of NO 2 under the experimental conditions is negligible. Variation of the surface to volume ratio and the nitrophenol concentration showed that the photolysis occurred in the gas phase indicating that HONO formation is initiated by intramolecular hydrogen transfer from the phenolic OH group to the nitro group. From the measured linear dependence of the HONO formation rate on the reactant's concentration and photolysis light intensity, a non-negligible new HONO source is proposed for the urban atmosphere during the day. Unexpectedly high HONO mixing ratios have been observed recently in several field campaigns during the day. It is proposed that the photolysis of aromatic compounds containing the ortho-nitrophenol entity could help to explain, at least in part, this high contribution of HONO to the oxidation capacity of the urban atmosphere.

Gas-Phase Reactions of Methoxyphenols with NO3 Radicals: Kinetics, Products, and Mechanisms

“…It was reported that reactivities of 2-nitrophenol toward OH and NO 3 radicals were slow, 60 and the atmospheric lifetimes were estimated to be 13 days and at least 2 days due to the reaction with OH and NO 3 radicals, respectively, whereas its photolysis rates was rapid. 64,65 Therefore, whether nitro derivatives observed in this study can be wood combustion tracers still needs to be further studied. In addition, alkyl groups with more than two C atoms formed double bonds, such as in the reaction of 4-ethylguaiacol with NO 3 radicals.…”

Near-Ultraviolet Absorption Cross Sections of Nitrophenols and Their Potential Influence on Tropospheric Oxidation Capacity

“…1 Atmospheric sources of nitrophenols include primary emissions from vehicles and secondary formation from tropospheric reactions of monoaromatic compounds with the hydroxyl radical, OH, in the presence of nitrogen oxides, or NO 3 -initiated oxidation of phenol and cresols. [2][3][4][5] Lately, nitrophenols in the gas phase have attracted attention as photolytic precursors of nitrous acid, HONO, [6][7] an important tropospheric species which readily photolyzes to form OH, the principal oxidant in the atmosphere. [8][9][10] Following this discovery, other ortho-nitroaromatics have been shown to photolyze to HONO or OH.…”

Measurements of HONO during BAQS-Met

“…Conversion efficiencies of NO 2 to HONO between 50 and close to 100% have been reported (Stemmler et al, 2006). Photolysis of ortho-nitrophenols has also been suggested as a relevant daytime production mechamism in the urban atmosphere (Bejan et al, 2006). An excellent overview of daytime HONO chemistry which examines daytime sources and sinks has been published (Kleffmann, 2007).…”