Enhancement of odd nitrogen modifies mesospheric ozone chemistry during polar winter

Abstract

Energetic particle precipitation (EPP) enhances odd nitrogen (NOx) in the polar upper atmosphere. Model studies have reported a solar cycle response in mesospheric ozone (O3) caused by EPP-related NOx enhancements which are included by applying a vertical NOx flux at around 80 km. However, it is not clear how O3 can be affected when the main chemical catalyst of odd oxygen (Ox = O + O(1D) + O3) loss in the mesosphere is odd hydrogen (HOx). Here we use a 1-D atmospheric model and show how enhanced NOx affects mesospheric chemistry and changes HOx partitioning, which subsequently leads to increase in Ox loss through standard HOx-driven catalytic cycles. Another, smaller increase of Ox loss results from HOx storage in HNO3 during night and its release by daytime photodissociation. Our results suggest that EPP, through NOx enhancements, could have a longer-term effect on mesospheric HOx and Ox in polar winter.