Abstract
Abstract. We quantified ambient mixing ratios of 9 monoterpenes, 6 sesquiterpenes, methyl chavicol, the oxygenated terpene linalool, and nopinone using an in-situ gas chromatograph with a quadrupole mass spectrometer (GC-MS). These measurements were a part of the 2007 Biosphere Effects on AeRosols and Photochemistry EXperiment (BEARPEX) at Blodgett Forest, a ponderosa pine forest in the Sierra Nevada Mountains of California. To our knowledge, these observations represent the first direct in-situ ambient quantification of the sesquiterpenes α-bergamotene, longifolene, α-farnesene, and β-farnesene. From average diurnal mixing ratio profiles, we show that α-farnesene emissions are dependent mainly on temperature whereas α-bergamotene and β-farnesene emissions are temperature- and light-dependent. The amount of sesquiterpene mass quantified above the canopy was small (averaging a total of 3.3 ppt during the day), but nevertheless these compounds contributed 7.6% to the overall ozone-olefin loss rate above the canopy. Assuming that the monoterpene-to-sesquiterpene emission rate in the canopy is similar to that observed in branch enclosure studies at the site during comparable weather conditions, and the average yield of aerosol mass from these sesquiterpenes is 10–50%, the amount of sesquiterpene mass reacted within the Blodgett Forest canopy alone accounts for 6–32% of the total organic aerosol mass measured during BEARPEX. The oxygenated monoterpene linalool was also quantified for the first time at Blodgett Forest. The linalool mass contribution was small (9.9 ppt and 0.74 ppt within and above the canopy, respectively), but it contributed 1.1% to the total ozone-olefin loss rate above the canopy. Reactive and semi-volatile compounds, especially sesquiterpenes, significantly impact the gas- and particle-phase chemistry of the atmosphere at Blodgett Forest and should be included in both biogenic volatile organic carbon emission and atmospheric chemistry models.
Highlights
Biogenic volatile organic compounds (BVOCs), including monoterpenes (C10H16), sesquiterpenes (C15H24), and oxygenated compounds, are important for atmospheric chemistry because they contribute to secondary organic aerosol (SOA) production and play an important role in the oxidative capacity of the atmosphere (Andreae and Crutzen, 1997; Fuentes et al, 2000)
We investigate the temporal changes in mixing ratios to elucidate controls over emissions and assess the contribution of the newly quantified BVOCs on: 1) the amount of carbon mass released by the ecosystem and 2) the above canopy ozone-olefin loss rate
Timelines of BVOC mixing ratios over the 7-week Biosphere Effects on AeRosols and Photochemistry EXperiment (BEARPEX) campaign are presented in conjunction with temperature and rainfall patterns (Fig. 1)
Summary
Biogenic volatile organic compounds (BVOCs), including monoterpenes (C10H16), sesquiterpenes (C15H24), and oxygenated compounds, are important for atmospheric chemistry because they contribute to secondary organic aerosol (SOA) production and play an important role in the oxidative capacity of the atmosphere (Andreae and Crutzen, 1997; Fuentes et al, 2000). Many studies indirectly suggest the presence of unmeasured highly reactive BVOCs in forest ecosystems (Di Carlo et al, 2004; Goldstein et al, 2004; Holzinger et al, 2005; Farmer and Cohen, 2008). This evidence highlights the importance of unmeasured BVOC compounds in understanding gasphase chemistry. These biogenic compounds can significantly impact SOA formation and growth.
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