Influence of reaction time and ozone concentration in flow tube studies of secondary organic aerosol formation from α-pinene ozonolysis

Nikolina Leona Serdarević1, Andreas Held1
1 Atmospheric Chemistry, University of Bayreuth

P 4.5 in BayCEERversity: Across scales, compartments & communities

Aerosol particles directly influence climate by absorbing and scattering light, and indirectly by influencing cloud formation and cloud properties. Secondary aerosols result from gas to particle conversion processes in the atmosphere. Some reactions leading to new particle formation involve the oxidation of organic precursor gases such as α-pinene. α-pinene is a monoterpene found in the oils of many species of coniferous trees. Ozone can quickly oxidize α-pinene forming, e.g. pinic and pinonic acid. These oxidation products contribute to the formation and growth of secondary organic aerosols. Depending on their size, newly formed particles have different physical properties. 
In this study, new particle formation experiments were conducted in a glass flow tube with constant concentrations of α-pinene, variable concentrations of ozone, and variable reaction times. After exiting the flow tube, particles were directed through an activated charcoal denuder in order to stop reactions and particle growth, and to remove ozone and precursor gases. After the denuder the size distribution of the formed aerosol was measured with a scanning mobility particle sizer (SMPS). The results have shown that reaction time and different ozone concentrations influence particle size and number concentration by means of proportional growth in size and number. Higher ozone concentrations lead to higher total number of particles and volume concentration whereas the particle diameter increases only up to 350 ppb of ozone. With prolongation of the reaction time, particle diameter as well as volume increase.

Keywords: secondary organic aerosol, new particle formation, α- pinene, ozone