On the importance of atmospheric loss of organic nitrates by aqueous-phase ●OH oxidation

Abstract

Abstract. Organic nitrates are secondary species in the atmosphere. Their fate is related to the chemical transport of pollutants from polluted areas to more distant zones. While their gas-phase chemistry has been studied, their reactivity in condensed phases is far from being understood. However, these compounds represent an important fraction of organic matter in condensed phases. In particular, their partition to the aqueous phase may be especially important for oxidized organic nitrates for which water solubility increases with functionalization. This work has studied for the first time the aqueous-phase ⚫OH-oxidation kinetics of four alkyl nitrates (isopropyl nitrate, isobutyl nitrate, 1-pentyl nitrate, and isopentyl nitrate) and three functionalized organic nitrates (α-nitrooxyacetone, 1-nitrooxy-2-propanol, and isosorbide 5-mononitrate) by developing a novel and accurate competition kinetic method. Low reactivity was observed, with kOH ranging from 8×107 to 3.1×109 L mol−1 s−1 at 296±2 K. Using these results, a previously developed aqueous-phase structure–activity relationship (SAR) was extended, and the resulting parameters confirmed the extreme deactivating effect of the nitrate group, up to two adjacent carbon atoms. The achieved extended SAR was then used to determine the ⚫OH-oxidation rate constants of 49 organic nitrates, including hydroxy nitrates, ketonitrates, aldehyde nitrates, nitrooxy carboxylic acids, and more functionalized organic nitrates such as isoprene and terpene nitrates. Their multiphase atmospheric lifetimes towards ⚫OH oxidation were calculated using these rate constants, and they were compared to their gas-phase lifetimes. Large differences were observed, especially for polyfunctional organic nitrates: for 50 % of the proposed organic nitrates for which the ⚫OH reaction occurs mainly in the aqueous phase (more than 50 % of the overall removal), their ⚫OH-oxidation lifetimes increased by 20 % to 155 % under cloud/fog conditions (liquid water content LWC = 0.35 g m−3). In particular, for 83 % of the proposed terpene nitrates, the reactivity towards ⚫OH occurred mostly (>98 %) in the aqueous phase, while for 60 % of these terpene nitrates, their lifetimes increased by 25 % to 140 % compared to their gas-phase reactivity. We demonstrate that these effects are of importance under cloud/fog conditions but also under wet aerosol conditions, especially for the terpene nitrates. These results suggest that considering aqueous-phase ⚫OH-oxidation reactivity of biogenic nitrates is necessary to improve the predictions of their atmospheric fate.

T- and pH-Dependent Kinetics of the Reactions of ·OH(aq) with Glutaric and Adipic Acid for Atmospheric Aqueous-Phase Chemistry

“…SI). Table summarizes the results of the two SAR calculations based on Doussin and Monod ,, and Minakata et al The influences of the two adjacent functional groups on each side of the CH 2 groups are taken into account in the method of Doussin and Monod, and therefore, the rate constants of the fully protonated, deprotonated, and fully deprotonated glutaric and adipic acids can be calculated. The results obtained using this SAR method are 7%, 28%, and 35% higher than the measured values for the H 2 A, HA – , and A 2– forms of glutaric acid, respectively, and 14%, 28%, and 50% higher than those for adipic acid, respectively.…”

“…Glutaric acid and adipic acid can also evaporate into the gas phase. The partitioning between gas and aqueous phase can be calculated as in eq , where n X ,gas and n X ,aq represent the mole number in the gas and aqueous phases, respectively, ρ is the density of water (in units of g m –3 ), LWC is the liquid water content (in units of g m –3 ), K H represents the Henry’s law constant (in units of mol L –1 atm –1 ), and R and T are the ideal gas constant (0.082 atm L mol –1 K –1 ) and the temperature (in units of K), respectively According to the previous publications, the K H of glutaric acid was reported as 2.4 × 10 9 and that of adipic acid was 6.7 × 10 9 mol L –1 atm –1 .…”

T- and pH-dependent OH radical reaction kinetics with glycine, alanine, serine, and threonine in the aqueous phase

“…The partitioning fractions of the amino acids in gas and aqueous phases can be calculated according to eqn (22), which includes the density of water ρ (in unit of g m −3 ), the liquid water content LWC (in unit of g m −3 ), the Henry's law constant k H (in unit of mol L −1 atm −1 ), the ideal gas constant R (0.082 atm L mol −1 K −1 ), and the Kelvin temperature T (in unit of K) . 73 The values of k H of Gly, Ala, Ser, and Thr were reported as 9.0 × 10 7 , 6.0 × 10 7 , 4.0 × 10 12 , and 1.4 × 10 10 mol L −1 atm −1 according to previous publications. 74,75 The LWC values in aerosols and cloud episodes were generally reported in the range of 10 −5 –1 g m −3 .…”

“…Activation parameters of the OH reactions with Gly, Ala, Ser, and Thr E A /kJ mol À1 A/L mol À1 s À1 AE 0.1) Â 10 9 1 AE 1 À(80 AE 2) 25 AE 11 Threonine HA AE 11 AE 1 (3.3 AE 0.1) Â 10 10 8 AE 1 À(52 AE 1) 24 AE 3 H 2 A + 12 AE 1 (5.0 AE 0.1) Â 10 10 10 AE 1 À(48 AE 1) 24 AE 2 (0.082 atm L mol À1 K À1), and the Kelvin temperature T (in unit of K) 73. …”

Aqueous‐Phase Secondary Processes and Meteorological Change Promote the Brown Carbon Formation and Transformation During Haze Events

“…As suggested in our previous study (Jiang et al., 2022),the molecular composition of P5 were mainly composed of low‐oxidized and unsaturated nitrogen‐containing molecules, which were mainly from primary emissions (e.g., vehicles emission) and aqueous‐phase SOA reactions of highly saturated compounds. However, multiphase photolysis and hydrolysis may also lead to the decomposition of these compounds (González‐Sánchez et al., 2023). Therefore, the aqueous‐phase SOA reactions under high RH in the afternoon may not lead to a largely increasing contribution of P5 in this study.…”