Review of Quantifying the nitrogen equilibrium and photochemistry-induced isotopic
effects between NO and NO2 by Li, Zhang, Michalski, Orlando and Tyndall.
This paper is a professional investigation of an important question that yields valuable
insight. Chamber experiments were carried out to measure the isotopic fractionation
factors of the Equilibrium Isotopic Effect (EIE) and the Leighton Cycle Induced Isotope
Effect (LCIE). A model was used to predict the variations that can be expected in field
measurements based on the EIE and LCIE. The experiments seem to yield valuable
results and my comments mainly concern model validation (limited because of lack
of data), and I am not convinced the LCIE result is perfectly general. I would like
to see more discussion regarding how the LCIE will change with the widely variable
conditions of the atmosphere including actinic flux spectrum, temperature, pressure,
concentrations of O3, RO2 and HO2, etc.