Photooxidation and ozonolysis of Δ3-carene and its oxidation product caronaldehyde in the atmospheric simulation chamber SAPHIR

Of the total global annual monoterpene emissions, Δ³-carene contributes 4.5 %, making it the 7^th most abundant monoterpene worldwide. As it is primarily emitted by pine trees, Δ³-carene can regionally gain in importance, for example in boreal forests and Mediterranean regions.  Oxidation products of monoterpenes such as organic nitrates and aldehydes are known to impact the formation of secondary pollutants such as ozone and particles, so understanding their atmospheric formation and fate is crucial.

The photooxidation and ozonolysis of Δ³-carene and the photooxidation and photolysis of its main daytime photooxidation product caronaldehyde were investigated in the atmospheric simulation chamber SAPHIR. Oxidation reactions were studied under atmospheric conditions with high (> 8 ppbv) and low (< 2 ppbv) NOx concentrations. Reaction rate constants of the reaction of Δ³-carene with OH and O₃, and of the reaction of caronaldehyde with OH as well as photolysis frequencies of caronaldehyde were determined. Production and destruction rates of the sum of hydroxyl and peroxy radicals (ROx = OH+HO2+RO2) were analysed to determine if there were unaccounted production and loss processes of radicals in the oxidation of Δ³-carene. The yield of Δ³-carene’s oxidation product caronaldehyde was determined from measured timeseries from OH photooxidation and ozonolysis experiments. Additionally, the OH yield from ozonolysis of Δ³-carene was determined.

Organic nitrate (RONO₂) yields of the reaction of RO₂ + NO, from RO₂ produced from the reactions of Δ³-carene and caronaldehyde with OH were determined by analyzing the reactive nitrogen species (NOy) in the chamber.