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Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NO_x from the atmosphere.

ABSTRACT: The formation of a suite of isoprene-derived hydroxy nitrate (IHN) isomers during the OH-initiated oxidation of isoprene affects both the concentration and distribution of nitrogen oxide free radicals (NO_x). Experiments performed in an atmospheric simulation chamber suggest that the lifetime of the most abundant isomer, 1,2-IHN, is shortened significantly by a water-mediated process (leading to nitric acid formation), while the lifetime of a similar isomer, 4,3-IHN, is not. Consistent with these chamber studies, NMR kinetic experiments constrain the 1,2-IHN hydrolysis lifetime to less than 10 s in deuterium oxide (D₂O) at 298 K, whereas the 4,3-IHN isomer has been observed to hydrolyze much less efficiently. These laboratory findings are used to interpret observations of the IHN isomer distribution in ambient air. The IHN isomer ratio (1,2-IHN to 4,3-IHN) in a high NO_x environment decreases rapidly in the afternoon, which is not explained using known gas-phase chemistry. When simulated with an observationally constrained model, we find that an additional loss process for the 1,2-IHN isomer with a time constant of about 6 h best explains our atmospheric measurements. Using estimates for 1,2-IHN Henry's law constant and atmospheric liquid water volume, we show that condensed-phase hydrolysis of 1,2-IHN can account for this loss process. Simulations from a global chemistry transport model show that the hydrolysis of 1,2-IHN accounts for a substantial fraction of NO_x lost (and HNO₃ produced), resulting in large impacts on oxidant formation, especially over forested regions.

SUBMITTER: Vasquez KT

PROVIDER: S-EPMC7777079 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

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Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NO<sub>x</sub> from the atmosphere.

Vasquez Krystal T KT Crounse John D JD Schulze Benjamin C BC Bates Kelvin H KH Teng Alexander P AP Xu Lu L Allen Hannah M HM Wennberg Paul O PO

Proceedings of the National Academy of Sciences of the United States of America 20201210 52

The formation of a suite of isoprene-derived hydroxy nitrate (IHN) isomers during the OH-initiated oxidation of isoprene affects both the concentration and distribution of nitrogen oxide free radicals (NO<sub>x</sub>). Experiments performed in an atmospheric simulation chamber suggest that the lifetime of the most abundant isomer, 1,2-IHN, is shortened significantly by a water-mediated process (leading to nitric acid formation), while the lifetime of a similar isomer, 4,3-IHN, is not. Consistent ...[more]

PMID: 33303653

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Project description:The nitrate radical (NO3) oxidation of isoprene is an important contributor to secondary organic aerosol (SOA). Isoprene has two double bonds which allow for multigeneration oxidation to occur. The effects of multigeneration chemistry on the gas- and particle-phase product distributions of the isoprene + NO3 system are not fully understood. In this study, we conduct chamber experiments by varying the ratio of N2O5 (precursor of NO3) to isoprene concentration from 1:1 to 14:1 to investigate the formation of products in both phases under different oxidation levels. Multigeneration chemistry leads to the formation of gas-phase products which then partition into particle phase depending on the product volatility; first-generation products (15-36% of total SOA) such as C5H9NO5 and C10H16N2O9 have volatility (log10C* = 1.0-3.0 using the partitioning method and log10C* = 2.6-4.5 using the formula method) 1-5 orders of magnitude higher than second-generation products (37-57% of total SOA, log10C* = -0.8-2.1 using the partitioning method and log10C* = -3.7-1.8 using the formula method) such as C5H8,10N2O8, C5H9N3O10, and C10H17N3O13. The fast reaction rate constants of first-generation products (estimated to be on the order of 10-13 cm3 molecules-1 s-1 at 295 K) and the lower volatility of second-generation products result in increased SOA yields when NO3 availability increases and multigeneration chemistry is enhanced. Specifically, an increase of up to 300% in SOA yield is observed when the N2O5/isoprene ratio increases from 1:1 to 3:1; from 5.7% (organic aerosol mass concentration, ΔM o = 4.2 μg/m3) to 16.3% (ΔM o = 11.9 μg/m3) when the reacted isoprene concentration is 25 ppb and from 3.1% (ΔM o = 1.2 μg/m3) to 12.4% (ΔM o = 5.4 μg/m3) when the reacted isoprene concentration is 15 ppb. The maximum SOA yield occurs when the N2O5/isoprene ratio is greater than or equal to 3:1 as a combined result of multigeneration chemistry and peroxy radicals (RO2) fate. We encourage future studies to consider both factors, which can vary under different laboratory and ambient conditions, when comparing SOA yields to better understand any differences observed. Our results highlight that multigeneration chemistry and the updated parameters including reaction rate constants and volatility distribution of products should be considered to enable a more comprehensive representation and prediction of SOA formation from NO3 oxidation of isoprene in atmospheric models.

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Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NO_x from the atmosphere.

Publications

Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NO<sub>x</sub> from the atmosphere.

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Dataset Information

Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NOx from the atmosphere.

Publications

Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NO<sub>x</sub> from the atmosphere.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

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Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NO_x from the atmosphere.