Measurements of J_(NO_3~-) in snow by nitrate-based actinometry

摘要

Chemical actinometry was used to measure nitrate photolysis rate coefficients, J_(NO_3~-), on and in snowpack at Summit, Greenland. Sealed glass tubes containing nitrate and a hydroxyl radical trapping system were buried in snow and exposed for between 2 and 24 h. Average J_(NO_3~-) values for 2-h midday exposures in early June on surface snow were 10- 14 × 10~(-7) s~(-1). Averages over 24 h were 3.5-4.5 × 10~(-7) s~(-1). These values reflect the integrated photon flux and also any variation of the nitrate photolysis rate with temperature. Attenuation of J_(NO_3~-) within the firn was 0.03-0.04 cm~(-1) for 24-h exposures and 0.08 cm~(-1) for a 2-h exposure. Different attenuation coefficients may relate to differential light penetration due to changes in sun angle over the course of 24 h.