Does Night-time Chemistry of Isoprene Impact Urban Air Quality in Polluted Environments?

Isoprene is a small organic compound that is predominantly emitted into the atmosphere by trees. It is the most emitted non-methane volatile organic hydrocarbon globally, meaning its chemistry is highly consequential for human health and climate around the world. Isoprene organonitrates are species which can be formed from the oxidation of isoprene by the hydroxyl (OH) or nitrate (NO3) radicals, and are of interest due to their potential to impact the chemical cycles that form HOx, NOx, and O3, as well as their ability to contribute to secondary organic aerosol (SOA). This thesis presents the results from a collection of modelling and experimental studies that investigate the oxidation of isoprene by NO3 and the chemistry of isoprene organonitrates. This work identifies crucial differences between the formation of some groups of organonitrates in existing chemical mechanisms; explores the importance of response factors in the analysis of isoprene organonitrates by Iodide Chemical Ionisation Mass Spectrometry (I-CIMS); investigates the impacts of changing NOx and O3 concentrations on the production of different organonitrates; highlights the importance of a small number of low-concentration high-volatility species for SOA formation; provides experimental evidence for the role of daytime NO3 chemistry under polluted conditions; presents measurements of nitrated epoxides from the NO3-initiated oxidation of isoprene; and describes measurements of several particle-phase isoprene oxidation products. These findings reveal the impact that isoprene nitrate chemistry can have on polluted environments, and provide direction for future investigations into isoprene chemistry and measurement of the resulting products.