Atmospheric particle formation from the ozonolysis of alkenes in the presence of SO2

Laboratory studies on the formation of new particles have been performed in a flow tube in the system O3/alkene/SO2 using α-pinene, trans-butene, and tetramethylethylene (TME) as model alkenes. Reactant concentrations were kept close to atmospheric conditions. In the absence of SO2, no particle formation was observed. The number of newly formed particles measured in the presence of SO2 was found to be H2SO4-controlled, whereas a distinct contribution of different organic products from the ozonolysis was not discovered. Scavenger experiments for OH radicals revealed that the main fraction of H2SO4 produced arose from OH+SO2. An additional pathway for H2SO4, probably Criegee Intermediate+SO2, accounted for 26% (α-pinene), 23% (trans-butene), and 42% (TME) of the total amount of H2SO4 formed. For conditions where particle formation occurred in the flow tube, H2SO4 concentrations of a few 107 molecule cm−3 were calculated, similar to observations in the atmosphere. Under the experimental conditions used, an analysis of the particle volume indicated that the organic ozonolysis products did not influence the particle growth significantly.