Observations of gas-phase products from the nitrate-radical-initiated oxidation of four monoterpenes

Abstract. Chemical ionization mass spectrometry with the nitrate reagent ion (NO3- CIMS) was used to investigate products of radical (NO3) initiated oxidation four monoterpenes in laboratory chamber experiments. α-Pinene, β-pinene, Δ-3-carene, and α-thujene were studied. The major gas-phase species produced each system distinctly different, showing effect monoterpene structure on mechanism further elucidating contributions these particle formation growth. By comparing groupings based ratios elements general formula CwHxNyOz, relative importance specific mechanistic pathways (fragmentation, termination, rearrangement) can be assessed for system. Additionally, measured time series highly oxidized reaction provide insights into ratio production loss rates high-molecular-weight Δ-3-carene effective O:C anticorrelated new intensity number concentration system; however, monomer : dimer had a small positive trend. Gas-phase yields by NO3- CIMS correlated concentrations system, exception α-thujene, which considerable amount low-volatility but no particles. Species-resolved wall found variable among our stainless steel chamber.