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Abstract. Chemical ionization mass spectrometry with the nitrate reagent ion (NO3- CIMS) was used to investigate the products of the nitrate radical(NO3) initiated oxidation of four monoterpenes in laboratory chamber experiments. α-Pinene, β-pinene, Δ-3-carene, andα-thujene were studied. The major gas-phase species produced in each system were distinctly different, showing the effect of monoterpenestructure on the oxidation mechanism and further elucidating the contributions of these species to particle formation and growth. By comparinggroupings of products based on the ratios of elements in the general formula CwHxNyOz, therelative importance of specific mechanistic pathways (fragmentation, termination, and radical rearrangement) can be assessed for eachsystem. Additionally, the measured time series of the highly oxidized reaction products provide insights into the ratio of relative production andloss rates of the high-molecular-weight products of the Δ-3-carene system. The measured effective O:C ratios of reaction products wereanticorrelated with new particle formation intensity and number concentration for each system; however, the monomer : dimer ratios of products had a smallpositive trend. Gas-phase yields of oxidation products measured by NO3- CIMS correlated with particle number concentrations for eachmonoterpene system, with the exception of α-thujene, which produced a considerable amount of low-volatility products but noparticles. Species-resolved wall loss was measured with NO3- CIMS and found to be highly variable among oxidized reaction products in ourstainless steel chamber.