Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NOx from the atmosphere. Journal Article uri icon

Overview

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 (NOx). 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 NOx 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 NOx lost (and HNO3 produced), resulting in large impacts on oxidant formation, especially over forested regions.

publication date

  • December 29, 2020

Date in CU Experts

  • June 27, 2021 5:54 AM

Full Author List

  • Vasquez KT; Crounse JD; Schulze BC; Bates KH; Teng AP; Xu L; Allen HM; Wennberg PO

author count

  • 8

Other Profiles

Electronic International Standard Serial Number (EISSN)

  • 1091-6490

Additional Document Info

start page

  • 33011

end page

  • 33016

volume

  • 117

issue

  • 52