Nitrate Photochemistry at the Air-Ice Interface and in Other Ice Reservoirs

Environ Sci Technol. 2018 May 15;52(10):5710-5717. doi: 10.1021/acs.est.8b00095. Epub 2018 Apr 26.

Abstract

The photolysis of snowpack nitrate (NO3-) is an important source of gaseous reactive nitrogen species that affect atmospheric oxidants, particularly in remote regions. However, it is unclear whether nitrate photochemistry differs between the three solute reservoirs in/on ice: in liquid-like regions (LLRs) in the ice; within the solid ice matrix; and in a quasi-liquid layer (QLL) at the air-ice interface, where past work indicates photolysis is enhanced. In this work, we explore the photoformation of nitrite in these reservoirs using laboratory ices. Nitrite quantum yields, Φ(NO2-), at 313 nm for aqueous and LLR ice samples agree with previous values, e.g., 0.65 ± 0.07% at -10 °C. For ice samples made via flash-freezing solution in liquid nitrogen, where nitrate is possibly present as a solid solution, the nitrite quantum yield is 0.57 ± 0.05% at -10 °C, similar to the LLR results. In contrast, the quantum yield at the air-ice interface is enhanced by a factor of 3.7 relative to LLRs, with a value of 2.39 ± 0.24%. These results indicate nitrate photolysis is enhanced at the air-ice interface, although the importance of this enhancement in the environment depends on the amount of nitrate present at the interface.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Nitrates*
  • Nitrites
  • Nitrogen Oxides*
  • Photochemistry
  • Photolysis

Substances

  • Nitrates
  • Nitrites
  • Nitrogen Oxides