Supporting data for: Observations of gas-phase products from the nitrate radical-initiated oxidation of four monoterpenes

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