Enhancement of odd nitrogen modifies mesospheric ozone chemistry during polar winter

Energetic particle precipitation (EPP) enhances odd nitrogen (NO x ) in the polar upper atmosphere. Model studies have reported a solar cycle response in mesospheric ozone (O 3 ) caused by EPP‐related NO x enhancements which are included by applying a vertical NO x flux at around 80 km. However, it is not clear how O 3 can be affected when the main chemical catalyst of odd oxygen (O x = O + O( 1 D) + O 3 ) loss in the mesosphere is odd hydrogen (HO x ). Here we use a 1‐D atmospheric model and show how enhanced NO x affects mesospheric chemistry and changes HO x partitioning, which subsequently leads to increase in O x loss through standard HO x ‐driven catalytic cycles. Another, smaller increase of O x loss results from HO x storage in HNO 3 during night and its release by daytime photodissociation. Our results suggest that EPP, through NO x enhancements, could have a longer‐term effect on mesospheric HO x and O x in polar winter.