Investigations into the gas-phase photolysis and OH radical kinetics of nitrocatechols: implications of intramolecular interactions on their atmospheric behaviour

Abstract

Abstract. The Environmental Simulation Chamber made of Quartz from the University “Alexandru Ioan Cuza” (ESC-Q-UAIC), at Iasi, Romania, was used to investigate the gas-phase reaction rate coefficients for four nitrocatechols toward OH radicals under simulated atmospheric conditions. Employing relative rate techniques at a temperature of 298 ± 2 K and a total air pressure of 1 atm, the obtained rate coefficients (in 10−12 cm3 s−1) were as follows: k3NCAT = (3.41 ± 0.37) for 3-nitrocatechol and k5M3NCAT = (5.55 ± 0.45) for 5-methyl-3-nitrocatechol at 365 nm, using CH3ONO photolysis as OH radicals source and dimethyl ether and cyclohexane as reference compounds, and k4NCAT = (1.27 ± 0.19) for 4-nitrocatechol and k4M5NCAT = (0.92 ± 0.14) for 4-methyl-5-nitrocatechol at 254 nm using H2O2 as OH radicals source and dimethyl ether and methanol as reference compounds. The photolysis rates in the actinic region, scaled to atmospheric relevant conditions by NO2 photolysis, were evaluated for 3-nitrocatechol and 5-methyl-3-nitrocatechol: J3NCAT = (3.06 ± 0.16) × 10−4 s−1 and J5M3NCAT = (2.14 ± 0.18) × 10−4 s−1, respectively. The photolysis rate constants at 254 nm were measured for 4-nitrocatechol and 4-methyl-5-nitrocatechol and the obtained values are J4NCAT = (6.7 ± 0.1) × 10−5 s−1 and J4M5NCAT = (3.2 ± 0.3) × 10−5 s−1. Considering the obtained results, our study suggests that photolysis may be the main degradation process for 3-nitrocatechol and 5-methyl-3-nitrocatechol in the atmosphere, with a photolytic lifetime in the atmosphere of up to 2 h. Results are discussed in terms of the reactivity of the four nitrocatechols under investigation toward OH-radical-initiated oxidation and their structural features. The rate coefficient values of the nitrocatechols are also compared with those estimated from the structure-activity relationship for monocyclic aromatic hydrocarbons and assessed in relation to their gas-phase IR spectra. Additional comparison with similar compounds is also presented, underlining the implications toward possible degradation pathways and atmospheric behaviour.

Characteristics and evolution of brown carbon in western United States wildfires

“…As noted above, 4-NC is less stable than bulk WS BrC, and in this plume it also displayed possible evidence of volatility-driven loss as it advected downwind, here, at an average rate of 5 % K −1 . For just these data, the 4-NC contributes ∼ 10 % of the total particle BrC absorption closest to the fire and the fraction decreases to ∼ 3 % when temperature increases from 287 to 303 K. To maintain a constant NEMR BrC despite a decrease of 4-NC, BrC production may have compensated for evaporation loss, such as gas-phase 4-NC and other volatile chromophores to less-volatile species that partitioned back to the aerosol phase (Roman et al, 2022). Alternatively, a temperature effect on the particle chemistry resulted in an unchanged BrC absorption.…”

Gas-Phase Ozone Reaction Kinetics of C5–C8Unsaturated Alcohols of Biogenic Interest

“…A Bruker Vertex 80 FT-IR spectrometer was used to collect IR spectra over a White type mirror system with an optical path length of 492 m at a resolution of 1 cm –1 . A more detailed description of the reactor can be found in literature . The relative kinetics method was employed for rate coefficient measurements using trans -2-butene and cyclohexene as reference compounds, with k ( trans -2-butene + O 3 ) = (2.00 ± 0.50) × 10 –17 cm 3 molecule –1 s –1 and k (cyclohexene + O 3 ) = (7.44 ± 1.86) × 10 –17 cm 3 molecule –1 s –1 .…”

“…A more detailed description of the reactor can be found in literature. 34 The relative kinetics method was employed for rate coefficient measurements using trans-2-butene and cyclohexene as reference compounds, with k(trans-2-butene + O 3 ) = (2.00 ± 0.50) × 10 −17 cm 3 molecule −1 s −135 and k(cyclohexene + O 3 ) = (7.44 ± 1.86) × 10 −17 cm 3 molecule −1 s −1 . 36 1,3,5-Trimethylbenzene was used as OH scavenger in concentrations such that more than 90% of any OH radicals produced were suppressed during the ozonolysis of unsaturated compounds.…”

Atmospheric breakdown chemistry of the new green solvent 2,2,5,5-tetramethyloxolane via gas-phase reactions with OH and Cl radicals

“…Relative rate experiments were conducted in the 760 dm 3 ESC-Q-UAIC environmental simulation chamber at "Alexandru Ioan Cuza" University of Iasi, Romania (Roman et al, 2022). The quartz chamber was equipped with inlet ports, sampling lines, 2 sets of UV lamps for photolysis at 365 nm (generation of OH or Cl-atoms) and at 254 nm (generation of OH), and FTIR instrumentation for observation of reference VOC, TMO, and TMO oxidation products.…”

“…Figure 3 displays FTIR spectra of TMO recorded at the CERNESIM atmospheric simulation chamber (Roman et al, 2022).…”