Daytime isoprene nitrates under changing NOx and O-3

Organonitrates are important species in the atmosphere due to their impacts on NOx, HOx, and O-3 budgets, and their potential to contribute to secondary organic aerosol (SOA) mass. This work presents a steady-state modelling approach to assess the impacts of changes in NOx and O-3 concentrations on the organonitrates produced from isoprene oxidation. The diverse formation pathways to isoprene organonitrates dictate the responses of different groups of organonitrates to changes in O-3 and NOx. For example, organonitrates predominantly formed from the OH-initiated oxidation of isoprene favour formation under lower-ozone and moderate-NOx concentrations, whereas organonitrates formed via daytime NO3 oxidation show the highest formation under high-O-3 concentrations with little dependence on NOx concentrations. Investigating the response of total organonitrates reveals complex and nonlinear behaviour with implications that could inform expectations of changes to organonitrate concentrations as efforts are made to reduce NOx and O-3 concentrations, including a region of NOx-O-3 space where total organonitrate concentration is relatively insensitive to changes in NOx and O-3. These conclusions are further contextualised by estimating the volatility of the isoprene organonitrates revealing the potential for high concentrations of low-volatility species under high-ozone conditions.

Automated summary

This study presents a modelling approach to assess the impacts of changes in NOx and O-3 concentrations on organonitrates produced from isoprene oxidation. Different formation pathways of isoprene organonitrates show different responses to O-3 and NOx concentrations. The study also reveals complex and nonlinear behavior of total organonitrates, which has important implications for understanding the changes in organonitrate concentrations under efforts to reduce NOx and O-3 concentrations.