Gas phase precursors to anthropogenic secondary organic aerosol: detailed observations of 1,3,5-trimethylbenzene photooxidation

Abstract

Abstract. A series of photooxidation experiments were conducted in an atmospheric simulation chamber in order to investigate the oxidation mechanism and secondary organic aerosol (SOA) formation potential of the model anthropogenic gas phase precursor, 1,3,5-trimethylbenzene. Alongside specific aerosol measurements, comprehensive gas phase measurements, primarily by Chemical Ionisation Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS), were carried out to provide detailed insight into the composition and behaviour of the organic components of the gas phase matrix during SOA formation. An array of gas phase organic compounds was measured during the oxidation process, including several previously unmeasured primary bicyclic compounds possessing various functional groups. Analysis of results obtained during this study implies that these peroxide bicyclic species along with a series of ring opening products and organic acids contribute to SOA growth. The effect of varying the VOC/NOx ratio on SOA formation was explored, as was the effect of acid seeding. It was found that low NOx conditions favour more rapid aerosol formation and a higher aerosol yield, a result that implies a role for organic peroxides in the nucleation process and SOA growth.

Online measurements of water-soluble organic acids in the gas and aerosol phase from the photooxidation of 1,3,5-trimethylbenzene

“…5 presents the aerosol mass concentration measured by the SMPS assuming a particle density ρ p of 1.4 g cm −3 (Alfarra et al, 2006). Particles sufficiently large to be detected are formed when the NO mixing ratio becomes low in the system, similarly to earlier observations (Ng et al, 2007;Wyche et al, 2009). The SOA particles reached mobility diameters up to ∼ 700 nm during the photooxidation of 1200 ppbv TMB in the absence of SO 2 .…”

“…5, solid lines), more SOA is produced at higher precursor concentration than with a lower precursor concentration but its formation starts later and the final diameter of the particles formed is larger. From the CPC data (not shown), particles larger than 3 nm can be observed after approximately 3.2 h after lights on during the experiments with 1200 ppbv TMB while in the case with 600 ppbv nucleation occurs already after 2 h of photooxidation (Wyche et al, 2009).…”

High summertime aerosol organic functional group concentrations from marine and seabird sources at Ross Island, Antarctica, during AWARE

“…This difference may be because the local emissions from McMurdo Station facilities reached the Cosray site in less than 5 min (since McMurdo Station was 2 km away and wind speeds were 6 m s −1 on average), making them essentially "fresh" primary particles, whereas those from the large upwind penguin colony took 6 h (since Cape Crozier was 100 km away and wind speeds were 6 m s −1 on average) to reach the site, giving them approximately 50 times more time for photochemical reactions leading to SOA production. It is also possible that the anthropogenic gas-phase precursor emissions had lower SOA acid yields but there is little evidence to support this (Rickard et al, 2010;Wyche et al, 2009;McNeill, 2015). The source of the vaporphase organic precursors of the summer seabird acid groups is not known, but given their substantial contribution to mass is worthy of further investigation.…”

The production and persistence of ΣRONO<sub>2</sub> in the Mexico City plume

“…In addition to uncertainty in the yield of nitrates from the initial oxidation of aromatic compounds, there is a high degree of uncertainty in the yields of ring-opening vs. ring-retaining products (Hamilton et al, 2003;Jenkin et al, 2003;Wagner et al, 2003;Wyche et al, 2009). The products of ringopening pathways could themselves have high nitrate yields and significant nitrate formation could thus result from oxidation of the first-generation products of aromatic oxidation.…”