Unraveling Pathways of Guaiacol Nitration in Atmospheric Waters: Nitrite, A Source of Reactive Nitronium Ion in the Atmosphere

Abstract

The tropospheric aqueous-phase aging of guaiacol (2-methoxyphenol, GUA), a lignocellulosic biomass burning pollutant, is addressed in this work. Pathways of GUA nitration in aqueous solution under atmospherically relevant conditions are proposed and critically discussed. The influence of NaNO2 and H2O2, hydroxyl radical scavenger, and sunlight was assessed by an experimental-modeling approach. In the presence of the urban pollutant, nitrite, GUA is preferentially nitrated to yield 4- and 6-nitroguaiacol. After a short lag-time, 4,6-dinitroguaiacol is also formed. Its production accelerates after guaiacol is completely consumed, which is nicely described by the model function accounting for NO2(•) and NO2(+) as nitrating agents. Although the estimated second-order kinetic rate constants of methoxyphenol nitration with NO2(•) are substantially higher than the corresponding rate constants of nitration with NO2(+), nitration rates are competitive under nighttime and liquid atmospheric aerosol-like conditions. In contrast to concentrations of radicals, which are governed by the interplay between diffusion-controlled reactions and are therefore mostly constant, concentrations of electrophiles are very much dependent on the ratio of NO2(-) to activated aromatics in solution. These results contribute substantially to the understanding of methoxyphenol aging in the atmospheric waters and underscore the importance of including electrophilic aromatic substitution reactions in atmospheric models.

Composition and mass size distribution of nitrated and oxygenated aromatic compounds in ambient particulate matter from southern and central Europe – implications for the origin

“…4-NC, MNCs, nitroguaiacols (NGs) and nitrosalicylic acids (NSAs) are predominantly formed by secondary oxidation of lignin thermal decomposition products (e.g. m-cresol, phenols, methoxyphenols, catechols, salicylic acid) in the gas and aqueous phases (Iinuma et al, 2010;Kelly et al, 2010;Kroflič et al, 2015;Frka et al, 2016;Teich et al, 2017;Finewax et al, 2018;Xie et al, 2017;Wang et al, 2019). Therefore, the yellow-coloured watersoluble 4-NC and MNCs have been proposed as suitable tracers for highly oxidized secondary BB aerosols (Iinuma et al, 2010;Kitanovski et al, 2012b;Kahnt et al, 2013;Caumo et al, 2016;Chow et al, 2016).…”

Kinetics of the Anaerobic Reaction of para‐Substituted Phenols with Nitrogen Dioxide

“…The occurrence of different mechanisms at different pHs is a frequent feature of NO 2 ● + HONO reactions The data of phenol reaction with HONO represented in Fig. show that the fastest rate takes place at low pH according to Reaction .…”

“…• + HONO reactions [18,20,21] The data of phenol reaction with HONO represented in Fig. 7 show that the fastest rate takes place at low pH according to Reaction (R5) [14,22].…”

Study of gas‐phase reactions of NO2+ with aromatic compounds using proton transfer reaction time‐of‐flight mass spectrometry

“…Nitronium ion (NO 2 + ) is not really one of the important gases atmospheric cations. It may play some roles in the heterogeneous chemistry of polar stratospheric clouds . While the study of ion chemistry involving the NO 2 + is currently the focus of considerable fundamental interest and is relevant in diverse fields ranging from mechanistic organic chemistry to atmospheric chemistry, clustering, and nucleation phenomena .…”

“…It may play some roles in the heterogeneous chemistry of polar stratospheric clouds . While the study of ion chemistry involving the NO 2 + is currently the focus of considerable fundamental interest and is relevant in diverse fields ranging from mechanistic organic chemistry to atmospheric chemistry, clustering, and nucleation phenomena . Aromatic compounds (ArXs) comprise 20% to 50% of the nonmethane hydrocarbon mass in urban air and are regarded as some of the main precursors to secondary organic aerosols (SOA), which constitute up to 80% of the total organic aerosol in the atmosphere .…”