Observations of Diurnal to Weekly Variations of Monoterpene-Dominated Fluxes of Volatile Organic Compounds from Mediterranean Forests: Implications for Regional Modeling

Abstract

The Estate of Castelporziano (Rome, Italy) hosts many ecosystems representative of Mediterranean vegetation, especially holm oak and pine forests and dune vegetation. In this work, basal emission factors (BEFs) of biogenic volatile organic compounds (BVOCs) obtained by Eddy Covariance in a field campaign using a proton transfer reaction−time-of-flight−mass spectrometer (PTR-TOF-MS) were compared to BEFs reported in previous studies that could not measure fluxes in real-time. Globally, broadleaf forests are dominated by isoprene emissions, but these Mediterranean ecosystems are dominated by strong monoterpene emitters, as shown by the new BEFs. The original and new BEFs were used to parametrize the model of emissions of gases and aerosols from nature (MEGAN v2.1), and model outputs were compared with measured fluxes. Results showed good agreement between modeled and measured fluxes when a model was used to predict radiative transfer and energy balance across the canopy. We then evaluated whether changes in BVOC emissions can affect the chemistry of the atmosphere and climate at a regional level. MEGAN was run together with the land surface model (community land model, CLM v4.0) of the community earth system model (CESM v1.0). Results highlighted that tropospheric ozone concentration and air temperature predicted from the model are sensitive to the magnitude of BVOC emissions, thus demonstrating the importance of adopting the proper BEF values for model parametrization.

Simulation of fine organic aerosols in the western Mediterranean area during the ChArMEx 2013 summer campaign

“…Unfortunately, to our best knowledge, no comparable studies exist in order to validate monoterpene emissions. For the Rome area, Italy, Fares et al (2013) concluded for a variety of typical Mediterranean tree and vegetation species mix, that MEGAN correctly simulated 10 mean observed monoterpene fluxes over the last two weeks of August 2007 within 10% error, as long as a canopy model was included (as in our study). meteorological parameters, the model can reproduce the daily concentration changes for these two species better than the hourly changes.…”

“…The local character of the comparisons for biogenic VOCs was pointed out, as well as the fact that biogenic OA is formed at a regional scale from these precursors rather than a 10 local scale. Available regional comparisons show acceptable comparisons for BVOC observed and simulated concentrations (Curci et al, 2010 ;Zare et al, 2012 ;Fares et al, 2013).Therefore, a systematic misrepresentation of BVOC in the model seem to be unlikely. For aerosol species, low bias was seen for BC, while an overestimation in simulations is observed for sulfates.…”

Isoprene emission potentials from European oak forests derived from canopy flux measurements: an assessment of uncertainties and inter-algorithm variability

“…In total, 14 days of isoprene flux measurements were collected at this site. More detailed information on the experimental site and flux tower set up can be found in Fares et al (2013). Eddy covariance measurements were performed on the top of a self-standing tower 37 m above ground, using a Gill HS-100 sonic anemometer for the measurement of high frequency vertical wind velocities.…”

Isoprenoid emissions by the Mediterranean vegetation in Castelporziano

“…The undisturbed Mediterranean mixed oak forest of Castelporziano represented an excellent study site to test a new instrument in an environment rich in highly reactive volatile compounds. The data on VOC emission have been reported by Fares et al (2013a) and basal emission factors for isoprene and monoterpenes are reported in Table 1, with monoterpenes totaling 1,760 lg m -2 h -1 , approximately three times the emission of isoprene. High levels of ozone deposition to the forest canopy up to -5,530 lg m -2 h -1 (Fares et al 2013b) suggested that reactive compounds originated in situ from the Mediterranean vegetation, and other reactive compounds of anthropogenic origin transported through polluted urban plumes from the close urban area of Rome could contribute to ozone removal at canopy level.…”

“…In plant ecosystems, a direct method to measure ozone losses by isoprenoids is not yet available, but micrometeorological techniques allow to quantify stomatal and total ozone deposition, therefore calculating non-stomatal ozone deposition by difference between these two terms. Results from experimental measurements showed that in the central hours of the day, when light and temperature maximize isoprenoid emissions, non-stomatal ozone deposition can be larger than stomatal deposition (Kurpius and Goldstein 2003;Fares et al 2010Fares et al , 2012Fares et al , 2013aGerosa et al 2005).…”