Measurement of Henry's law and liquid-phase loss rate constants of peroxypropionic nitric anhydride (PPN) in deionized water and in n-octanol

The Henry's law solubility ( 𝐻 S ) and liquid-phase loss rate constants ( k l ) of the tropospheric trace gas constituents peroxyacetic nitric anhydride (PAN, CH 3 C(O)O 2 NO 2 ; commonly known as peroxyacetyl 15 nitrate) and peroxypropionic nitric anhydride (PPN, C 2 H 5 C(O)O 2 NO 2 ; also known as peroxypropionyl nitrate) in deionized (DI) water and of PPN in n-octanol were measured using a flow bubble apparatus at temperatures between 5.0 °C and 25.0 °C. For PAN in DI water, the observed values for 𝐻 S,aq are consistent with literature, whereas the solubility of PPN in DI water is slightly lower than literature values, ranging from 𝐻 S𝐶𝑃 (PPN) aq = (1.49±0.05) M atm -1 at 25.0 °C to 𝐻 S𝐶𝑃 (PPN) aq = (7.01±0.25) M atm -1 at 5.0 °C (stated 20 uncertainties are at the 1σ level). The data are best described by ln( 𝐻 S𝐶𝑃 (PAN) aq /[M atm -1 ]) = - (17.8±0.3) + (5620±85)/ T and ln( 𝐻 S𝐶𝑃 (PPN) aq /[M atm -1 ]) = -(19.5±1.7) + (5955±480)/ T where T is in Kelvin. For n-octanol, the PPN solubility ranges from 𝐻 S𝐶𝑃 (PPN) oct = (88±5) M atm -1 at 25.0 °C to 𝐻 S𝐶𝑃 oct = (204±16) M atm -1 at 5.0 °C and is best described by ln( 𝐻 S𝐶𝑃 (PPN) oct /[M atm -1 ]) = -(6.92±0.75) + (3390±320)/ T . n-Octanol-water partition coefficients ( K OW ) for PPN were determined for the first time, ranging from 59±4 25 at 25.0 °C to 29±3 at 5.0 °C. Observed loss rate constants in DI water are consistent with recent literature and larger than the thermal dissociation rates for both PAN and PPN, consistent with a hydrolysis mechanism, whereas k l values in n-octanol are significantly smaller than gas-phase dissociation rate constants, likely owing to a "cage effect" in the organic liquid. The results imply that uptake of either PAN or PPN on cloud water and organic aerosol is negligible but that uptake of PPN may constitute an 30 overlooked source of peroxy radicals in organic aerosol.