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Biogenic volatile organic compounds (VOCs) are a significant source of global secondary organic aerosol (SOA); however, quantifying their aerosol forming potential remains a challenge. This study presents smog chamber laboratory work, focusing on SOA formation via oxidation of the emissions of two dominant tree species from boreal forest area, Scots pine (<i>Pinus sylvestris</i> L.) and Norway spruce (<i>Picea abies</i>), by hydroxyl radical (OH) and ozone (O₃). Oxidation of &alpha;-pinene was also studied as a reference system. Tetramethylethylene (TME) and 2-butanol were added to control OH and O₃ levels, thereby allowing SOA formation events to be categorized as resulting from either OH-dominated or O₃-initiated chemistry. SOA mass yields from &alpha;-pinene are consistent with previous studies while the yields from the real plant emissions are generally lower than that from &alpha;-pinene, varying from 1.9% at an aerosol mass loading of 0.69 μg m^&minus;3 to 17.7% at 26.0 μg m⁻³. Mass yields from oxidation of real plant emissions are subject to the interactive effects of the molecular structures of plant emissions and their reaction chemistry with OH and O₃, which lead to variations in condensable product volatility. SOA formation can be reproduced with a two-product gas-phase partitioning absorption model in spite of differences in the source of oxidant species and product volatility in the real plant emission experiments. Condensable products from OH-dominated chemistry showed a higher volatility than those from O₃-initiated systems during aerosol growth stage. Particulate phase products became less volatile via aging process which continued after input gas-phase oxidants had been completely consumed.