Evaluation of 1,3,5 trimethylbenzene degradation in the detailed tropospheric chemistry mechanism, MCMv3.1, using environmental chamber data

Abstract

Abstract. The degradation mechanism of 1,3,5-trimethyl- benzene (TMB) as implemented in the Master Chemical Mechanism version 3.1 (MCM) was evaluated using data from the environmental chamber at the Paul Scherrer Institute. The results show that the MCM provides a consistent description of the photo-oxidation of TMB/NOx mixtures for a range of conditions. In all cases the agreement between the measurement and the simulation decreases with decreasing VOC-NOx ratio and in addition with increasing precursor concentration. A significant underestimation of the decay rate of TMB and thus underestimation of reactivity in the system, consistent with results from previous appraisals of the MCM, was observed. Much higher nitrous acid (HONO) concentrations compared to simulations and expected from chamber characterization experiments were measured during these smog chamber experiments. A light induced NO2 to HONO conversion at the chamber walls is suggested to occur. This photo-enhanced NO2 to HONO conversion with subsequent HONO photolysis enhances the reactivity of the system. After the implementation of this reaction in the model it describes the decay of TMB properly. Nevertheless, the model still over-predicts ozone at a later stage of the experiment. This can be attributed to a too slow removal of NO2. It is also shown that this photo-enhanced HONO formation is not restricted to TMB photo-oxidation but also occurs in other chemical systems (e.g. α-pinene). However, the influence of HONO as a source of OH radicals is less important in these more reactive systems and therefore the importance of the HONO chemistry is less obvious.

Measurements of VOCs by proton transfer reaction mass spectrometry at a rural Ontario site: Sources and correlation to aerosol composition

“…There is also a tight connection between the overall organic mass concentration and select VOCs observed during the campaign, as shown in Figures 11 and 12. It is well known that formation of gas‐phase carbonyls has been observed in smog‐chamber experiments that investigated SOA formation from biogenic and anthropogenic VOCs [ Lee et al , 2006a, 2006b; Metzger et al , 2008; Wisthaler et al , 2001]. The correspondence is best with acetone, which has anthropogenic and biogenic sources, both primary and secondary (Figure 12).…”

“…as terpene [Lee et al, 2006a[Lee et al, , 2006b or aromatic oxidation product in case of m/z 113 [Metzger et al, 2008]. The time profile of F3 is remarkably well correlated with the oxygenated organic aerosol component, OOA, that is derived from a PMF analysis of Aerosol Mass Spectrometer aerosol composition data collected during the study [Slowik et al, 2009a].…”

Development and chamber evaluation of the MCM v3.2 degradation scheme for β-caryophyllene

“…For illustrative simulation of the photo-oxidation experiment in the Caltech chamber, reported by Lee et al (2006b), a representative blacklight spectrum emitting over the range 330-400 nm (λ max ≈355 nm) was assumed, and the intensity was scaled to provide simulated profiles of β-caryophyllene, NO x and ozone that were comparable with those reported. The impact of chamber wall effects for simulations of the ACES experiments was represented using the mechanism characterized for the PSI chamber, as reported by Metzger et al (2008), that being an FEP Teflon chamber of similar volume and light source to the Manchester chamber. The auxiliary mechanism includes a conventional description of wall sources of radicals and the reactivity of background organics, and adsorption or desorption of oxidised nitrogen species.…”

“…On the basis of the critical appraisal of Barley and McFiggans (2010), the applied values of p • L were calculated using the method of Nannoolal et al (2008), in conjunction with species boiling temperatures estimated by the method of Nannoolal et al (2004). For simplicity, all vapour pressures applied in the current work were calculated for a temperature of 298 K. The value used for p • L for a given species clearly has a critical impact on the calculated value of K p , but estimating p • L values for complex multifunctional oxygenates remains subject to considerable uncertainty, as very few quantitative data are available for checking the predicted values.…”

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

“…The presence of SO 2 increases the nucleation rate as described in Metzger et al (2010): it is possible to observe particles in the CPC (>3 nm) already after 1 hour of photooxidation (1200 ppbv TMB). The slightly higher final aerosol mass concentration produced in the presence of SO 2 during the high concentration experiments is probably explained by the earlier particle formation, resulting in lower vapour wall losses of low-volatility oxidation products.…”