Ozonolysis of α-Pinene and Δ³-Carene Mixtures: Formation of Dimers with Two Precursors

Abstract

The formation of secondary organic aerosol (SOA) from the structurally similar monoterpenes, α-pinene and Δ 3 -carene, differs substantially. The aerosol phase is already complex for a single precursor, and when mixtures are oxidized, products, e.g., dimers, may form between different volatile organic compounds (VOCs). This work investigates whether differences in SOA formation and properties from the oxidation of individual monoterpenes persist when a mixture of the monoterpenes is oxidized. Ozonolysis of α-pinene, Δ 3 -carene, and a 1:1 mixture of them was performed in the Aarhus University Research on Aerosol (AURA) atmospheric simulation chamber. Here, ∼100 ppb of monoterpene was oxidized by 200 ppb O 3 under dark conditions at 20 °C. The particle number concentration and particle mass concentration for ozonolysis of α-pinene exceed those from ozonolysis of Δ 3 -carene alone, while their mixture results in concentrations similar to α-pinene ozonolysis. Detailed offline analysis reveals evidence of VOC-cross-product dimers in SOA from ozonolysis of the monoterpene mixture: a VOC-crossproduct dimer likely composed of the monomeric units cis-caric acid and 10-hydroxy-pinonic acid and a VOC-cross-product dimer ester likely from the monomeric units caronaldehyde and terpenylic acid were tentatively identified by liquid chromatography-mass spectrometry. To improve the understanding of chemical mechanisms determining SOA, it is relevant to identify VOC-crossproducts.

The effect of temperature and relative humidity on secondary organic aerosol formation from ozonolysis of Δ3-carene

“…A slight temperature trend is observed with an increasing O/C ratio with increasing temperature for dry experiments. Previous studies with ozonolysis of Δ 3 -carene at 50 ppb 34 and 100 ppb 35 and ozone concentration of about 200 ppb, respectively, both show O/C ratios of about 0.4. In this work, the O/C ratio for experiments 10A–C lies at about 0.45–0.5, which indicates a more oxidised particle phase.…”

“…The particle extracts were stored at 5 °C until analysis. The analysis was performed according to Thomsen et al 35 with an ultra-high performance liquid chromatograph (UHPLC) coupled to a quadrupole time-of-flight mass spectrometer (QTOF-MS, Compact, Bruker) through an electrospray inlet. The UHPLC method and QTOF-MS settings are described briefly in Section 6 in the ESI† and a detailed description is found elsewhere.…”

“…The absolute uncertainty on the D 3 -carene concentration is based on previous measurements. 34,35 The uncertainty in the O 3 concentration is estimated based on the noise and instrument accuracy. The uncertainty on the SOA yield is based on the uncertainty of the SMPS measurements and the absolute uncertainty of the D concentrations of 10 ppb and the assumption that all D 3 -carene is consumed.…”

“…This likely stems from the lower VOC loading in this work, while the ozone concentration is similar to the previous studies. 34,35 It seems that there is an effect of relative humidity on the H/C ratio for the ozonolysis of 10 ppb In the offline analysis, four carboxylic acids, cis-3-caric acid, cis-3-caronic acid, OH-3-caronic acid (10-hydroxy-3-caronic acid), and a carboxylic acid with molecular weight (MW) 170 g mol −1 , are tentatively identied. MW170 is tentatively identied as 3-caralic acid or nor-3-caronic acid.…”

The driving effects of common atmospheric molecules for formation of clusters: the case of sulfuric acid, nitric acid, hydrochloric acid, ammonia, and dimethylamine

“…8–14 Thus, an incredible amount of experimental and computational effort has been devoted to understanding which species are involved, and how they combine together, to form secondary aerosols. 6,8–85 It is common in the field to work under the assumption that acids and bases grow into an ensemble that contains an equal number of both types of molecules. 8–14 Yet, the tremendous number of potential compounds that can form prenucleation clusters is vast, and there is no experimental technique that can identify all of the different molecules in prenucleation complexes or small aerosols in the sub-nanometer (nm) to nm size range.…”