Ambient observations of dimers from terpene oxidation in the gas phase: Implications for new particle formation and growth

Abstract

We present ambient observations of dimeric monoterpene oxidation products (C16–20HyO6–9) in gas and particle phases in the boreal forest in Finland in spring 2013 and 2014, detected with a chemical ionization mass spectrometer with a filter inlet for gases and aerosols employing acetate and iodide as reagent ions. These are among the first online dual‐phase observations of such dimers in the atmosphere. Estimated saturation concentrations of 10−15 to 10−6 µg m−3 (based on observed thermal desorptions and group‐contribution methods) and measured gas‐phase concentrations of 10−3 to 10−2 µg m−3 (~106–107 molecules cm−3) corroborate a gas‐phase formation mechanism. Regular new particle formation (NPF) events allowed insights into the potential role dimers may play for atmospheric NPF and growth. The observationally constrained Model for Acid‐Base chemistry in NAnoparticle Growth indicates a contribution of ~5% to early stage particle growth from the ~60 gaseous dimer compounds.

Semi-volatile and highly oxygenated gaseous and particulate organic compounds observed above a boreal forest canopy

“…8a). While there are few, if any, reports of such nitrated dimers in both the gas and particle phases, there is evidence from offline analyses of particlephase SOA of nitrate oligomers (Nguyen et al, 2011). That we observed some of these dimers enhanced at night is suggestive of a possible role for NO 3 radical chemistry.…”

α-pinene secondary organic aerosol at low temperature: Chemical composition and implications for particle viscosity

“…The resulting mass spectral signal evolutions as a function of desorption 185 temperature are termed thermograms . Single mode thermograms of a compound with signal maxima occurring at distinct desorption temperatures (Tmax), which correlate with the compound's enthalpy of sublimation, can be used to infer its saturation vapor pressure (Lopez-Hilfiker et al, 2015;Mohr et al, 2017). Multi-mode thermograms indicate contributions from isomers having different vapor pressures, or thermal fragmentation of larger molecules during the heating of the filter (Lopez-Hilfiker et al, 2015).…”

“…These thermograms result from the thermal desorption of particles deposited on the Teflon filter in the FIGAERO . Single mode thermograms 295 of a compound with a signal maximum occurring at a distinct desorption temperature (Tmax) can be used to infer the compound's saturation vapor pressure (Lopez-Hilfiker et al, 2015;Mohr et al, 2017). However, evaporative behavior and inferred volatility of a particle-bound compound are also influenced by the particles' physical phase state, particle phase diffusivity and viscosity (Yli-Juuti et al, 2017).…”

“…Less oxygenated dimers (e.g. esters and other accretion products), some of which have similarly low volatility as HOM and for many of which formation mechanisms are still not known, are major products in aerosol particles from α-pinene ozonolysis, and have been proposed as key components in organic particle growth in field and laboratory (Kristensen et al, 2014;75 Kristensen et al, 2016;Tröstl et al, 2016;Mohr et al, 2017).…”

An electrospray chemical ionization source for real-time measurement of atmospheric organic and inorganic vapors

“…These dimers have compositions ranging, for example, from C 15 H 26 O 3 to C 20 H 32 O 7 . We note that many of these dimers have been recently detected in the gas phase using a low-pressure iodideadduct HR-ToF-CIMS in a boreal forest environment (Mohr et al, 2017). Thus, while the lower detection efficiency of dimers in this work using I − or NO − 3 may be from differences in reagent ion sensitivities, we suspect that differences in ion optic settings between negative and positive ion modes that affect ion transmission efficiencies at large massto-charge ratios is a more likely explanation.…”