Measurements of JNO3− in snow by nitrate-based actinometry

Chemical actinometry was used to measure nitrate photolysis rate coefficients, JNO3−, 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 JNO3− 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 JNO3− 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.