This PhD thesis aims to improve the knowledge on the processes and chemical species in the gas- and particle-phases that are involved in the production of secondary organic aerosol (SOA) from monoterpene oxidation in the atmosphere. A denuder/filter technique that enabled the simultaneous sampling of gaseous and particulate compounds was applied in the present study. The sampling technique was comprehensively characterised and optimised using twelve atmospherically relevant carbonyl compounds. The present study improved the denuder coating procedure and the sampling performance. An additional coating with the derivatisation reagent, 2,4‑dinitrophenylhydrazine (DNPH), reduced the break-through potential (e.g., from 98% to 0.9% for methyl vinyl ketone) and the fraction of carbonyl compounds on the filter material (e.g., from 8.7% to 0% for acetone). Calibration experiments against an aerosol chamber were performed to reduce the relative standard deviation (RSD) of the calibration points in the denuder measurements. The RSDs were reduced by half for acetone, acetaldehyde, methyl vinyl ketone, glyoxal, benzaldehyde and campholenic aldehyde using a XAD‑4/DNPH denuder, and the quantification error was also reduced. This sampling technique was then applied to a series of α- and β-pinene ozonolysis experiments. The present study examined the influence of an OH radical scavenger (CO), and hence the HO2/RO2 ratio, on the SOA formation, product distribution and partitioning behaviour of selected oxidation products in conjunction with different seed particle acidities. It was shown that SOA yields increased by about 8% in α-pinene ozonolysis when CO and acidic seed particles co-existed, whereas only a marginal difference was observed (increase of 2%) for β-pinene compared to neutral seed particles. From the denuder/filter sample analysis, it was possible to tentatively identify a new compound from the α-pinene ozonolysis, i.e., terpenylic aldehyde. Gas- and particle-phase yields were estimated for the first time for this compound (i.e., 1% and 0.4%, respectively). The atmospheric relevance of terpenylic aldehyde was demonstrated based on ambient filter measurements and a possible formation pathway was suggested. Furthermore, the present study provided an additional explanation for enhanced SOA formation when acidic seed particles are used in monoterpene ozonolysis. It was demonstrated that the isomerisation of monoterpene oxides on acidic seed particles leads to the formation of highly reactive SOA precursors, whose subsequent reaction with ozone contributes significantly to SOA formation.

This PhD thesis aims to improve the knowledge on the processes and chemical species in the gas- and particle-phases that are involved in the production of secondary organic aerosol (SOA) from monoterpene oxidation in the atmosphere. A denuder/filter technique that enabled the simultaneous sampling of gaseous and particulate compounds was applied in the present study. The sampling technique was comprehensively characterised and optimised using twelve atmospherically relevant carbonyl compounds. The present study improved the denuder coating procedure and the sampling performance. An additional coating with the derivatisation reagent, 2,4‑dinitrophenylhydrazine (DNPH), reduced the break-through potential (e.g., from 98% to 0.9% for methyl vinyl ketone) and the fraction of carbonyl compounds on the filter material (e.g., from 8.7% to 0% for acetone). Calibration experiments against an aerosol chamber were performed to reduce the relative standard deviation (RSD) of the calibration points in the denuder measurements. The RSDs were reduced by half for acetone, acetaldehyde, methyl vinyl ketone, glyoxal, benzaldehyde and campholenic aldehyde using a XAD‑4/DNPH denuder, and the quantification error was also reduced. This sampling technique was then applied to a series of α- and β-pinene ozonolysis experiments. The present study examined the influence of an OH radical scavenger (CO), and hence the HO2/RO2 ratio, on the SOA formation, product distribution and partitioning behaviour of selected oxidation products in conjunction with different seed particle acidities. It was shown that SOA yields increased by about 8% in α-pinene ozonolysis when CO and acidic seed particles co-existed, whereas only a marginal difference was observed (increase of 2%) for β-pinene compared to neutral seed particles. From the denuder/filter sample analysis, it was possible to tentatively identify a new compound from the α-pinene ozonolysis, i.e., terpenylic aldehyde. Gas- and particle-phase yields were estimated for the first time for this compound (i.e., 1% and 0.4%, respectively). The atmospheric relevance of terpenylic aldehyde was demonstrated based on ambient filter measurements and a possible formation pathway was suggested. Furthermore, the present study provided an additional explanation for enhanced SOA formation when acidic seed particles are used in monoterpene ozonolysis. It was demonstrated that the isomerisation of monoterpene oxides on acidic seed particles leads to the formation of highly reactive SOA precursors, whose subsequent reaction with ozone contributes significantly to SOA formation.