Measurement of Henry's law constants of ethyl nitrate in deionized water, synthetic sea salt solutions, and n-octanol

Abstract

Ethyl nitrate (EN; C2H5ONO2) is an important component of atmospheric “odd nitrogen” (NOy) whose main source is marine emissions. To correctly describe its air-water transfer and model its global distribution, accurate values for its temperature- and salinity-dependent Henry's law solubility constants are needed. Here, we report Henry's law (HScp) constants for EN in deionized (DI) water, synthetic sea salt solutions (SSS), and n-octanol at temperatures between 278.2 K and 303.2 K. For DI water, HScp constants of (2.03 ± 0.06) M atm−1 at 293.2 K and (4.88 ± 0.13) M atm−1 at 278.2 K were observed (all stated uncertainties are at the 1σ level). The data are best described by ln(HScp(aq)/[Matm−1]) = -(16.2 ± 0.4)+(4.94 ± 0.11) × 103/T and ln(HScp(octanol)/[Matm−1]) = -(11.1 ± 1.9)+(4.15 ± 0.33) × 103/T, from which the octanol-water partition coefficient (KOW) was calculated. A temperature-independent salting-out factor of 1.25 ± 0.03 and Setschenow constant of KS = (0.33 ± 0.04) mol kg−1 were determined for SSS. Liquid-phase losses of EN were negligible in all solvents (kl < 1 × 10−4 s−1). The HScp(aq) values agree with results by Kames (1993) but are between 2% (at 303.2 K) and 19% (at 278.2 K) lower than the widely used parameterization by Kames and Schurath (1992), indicating a systemic bias in the EN literature and modelling of the Earth's nitrogen cycle.