[1] Frost flowers, intricate featherlike crystals that grow on refreezing sea ice leads, have been implicated in lower atmospheric chemical reactions. Few studies have presented chemical composition information for frost flowers over time and many of the chemical species commonly associated with Polar tropospheric reactions have never been reported for frost flowers. We undertook this study on the sea ice north of Barrow, Alaska to quantify the major ion, stable oxygen and hydrogen isotope, alkalinity, light absorbance by soluble species, organochlorine, and aldehyde composition of seawater, brine, and frost flowers. For many of these chemical species we present the first measurements from brine or frost flowers. Results show that major ion and alkalinity concentrations, stable isotope values, and major chromophore (NO 3 À and H 2 O 2 ) concentrations are controlled by fractionation from seawater and brine. The presence of these chemical species in present and future sea ice scenarios is somewhat predictable. However, aldehydes, organochlorine compounds, light absorbing species, and mercury (part 2 of this research and Sherman et al. (2012)) are deposited to frost flowers through less predictable processes that probably involve the atmosphere as a source. The present and future concentrations of these constituents in frost flowers may not be easily incorporated into future sea ice or lower atmospheric chemistry scenarios. Thinning of Arctic sea ice will likely present more open sea ice leads where young ice, brine, and frost flowers form. How these changing ice conditions will affect the interactions between ice, brine, frost flowers and the lower atmosphere is unknown.

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The observation, that absorption of light by concentrated sulphuric acid at wavelengths near 193 nm apparently tends to zero as the acid is progressively purified, is supported by ab initio calculations of the energies of the three lowest excited states of monomeric H 2 SO 4 . The electronic-structure calculations indicate that the lowest excited state is not accessible by single-photon absorption for light of wavelengths >150 nm. This limit includes a generous allowance for error; the calculated energy of the transition corresponds to a wavelength <120 nm. Previous observations of photoluminescence and photo-oxidation of CO in sulphuric acid aerosols are attributed to multiphoton processes, caused by internal focusing of the incident light by the aerosol droplets. This finding does not rule out the occurrence of significant photochemistry of sulphuric acid aerosols in the stratospheres of the Earth and Venus, because of the likely presence of transition-metal ions as impurities in the atmospheric aerosols.

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