Abstract
Abstract. 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 (Pinus sylvestris L.) and Norway spruce (Picea abies), by hydroxyl radical (OH) and ozone (O3). Oxidation of α-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 α-pinene are consistent with previous studies while the yields from the real plant emissions are generally lower than that from α-pinene, varying from 1.9% at an aerosol mass loading of 0.69 μg m−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.
Highlights
The largest uncertainties in predicting anthropogenic influences on climate are associated with global aerosol burdens
Biogenic volatile organic compounds (VOCs) (BVOC) emissions contribute an overwhelming fraction of 90% of the overall VOC emissions (Guenther et al, 1995), which underscores the importance of biogenic VOC (BVOC) as a significant source of secondary organic aerosol (SOA)
After addition of BVOCs and oxidants, the inlet flow was turned off and the chamber was operated in batch-mode; i.e., the chamber was gradually emptied by sample flows to the instruments
Summary
The largest uncertainties in predicting anthropogenic influences on climate are associated with global aerosol burdens. In order to mimic more realistic atmospheric conditions, recent studies have been carried out to investigate SOA formation using direct biogenic emissions in the laboratory, varying from macroalgae (McFiggans et al, 2004), herbaceous plant white cabbage (Joutsensaari et al, 2005; Pinto et al, 2007) to the woody plant, oak and loblolly pine (Lang-Yona et al, 2010; VanReken et al, 2006) and silver birch, Scots pine and Norway spruce (Mentel et al, 2009; Hao et al, 2009; Kiendler-Scharr et al, 2009a, b; Vaattovaara et al, 2009; Virtanen et al, 2010) Most of these studies focused on the phenomenon of new particle formation, rarely reporting SOA mass yields (Mentel et al, 2009; Lang-Yona et al, 2010). This approach is expected to give more realistic, quantitative yields, which can be incorporated in global aerosol models
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