Contribution of flowering trees to urban atmospheric biogenic volatile organic compound emissions

[摘要] Emissions of biogenic volatile organic compounds (BVOC) from urban treesduring and after blooming were measured during spring and early summer 2009in Boulder, Colorado. Air samples were collected onto solid adsorbentcartridges from branch enclosures on the tree species crabapple (Malus sp.),horse chestnut (Aesculus carnea, "Ft. McNair"), honey locust (Gleditsiatriacanthos, "Sunburst"), and hawthorn (Crataegus laevigata, "PaulsScarlet"). These species constitute ~ 65% of theinsect-pollinated fraction of the flowering tree canopy (excludingcatkin-producing trees) from the street area managed by the City of Boulder.Samples were analyzed for C₁₀–C₁₅ BVOC by thermal desorption andgas chromatography coupled to a flame ionization detector and a massspectrometer (GC/FID/MS). Identified emissions and emission rates from thesefour tree species during the flowering phase were found to vary over a widerange. Monoterpene emissions were identified for honey locust, horse chestnutand hawthorn. Sesquiterpene emissions were observed in horse chestnut andhawthorn samples. Crabapple flowers were found to emit significant amounts ofbenzyl alcohol and benzaldehyde. Floral BVOC emissions increased withtemperature, generally exhibiting exponential temperature dependence. Changesin BVOC speciation during and after the flowering period were observed forevery tree studied. Emission rates were significantly higher during theblooming compared to the post-blooming state for crabapple and honey locust.The results were scaled to the dry mass of leaves and flowers contained inthe enclosure. Only flower dry mass was accounted for crabapple emissionrates as leaves appeared at the end of the flowering period. Total normalized(30 °C) monoterpene emissions from honey locust were higher duringflowering (5.3 μgC g⁻¹ h⁻¹) than after flowering(1.2 μgC g⁻¹ h⁻¹). The total normalized BVOC emissionrate from crabapple (93 μgC g⁻¹ h⁻¹) during theflowering period is of the same order as isoprene emissions from oak trees,which are among the highest BVOC flowering period floral emissions observedfrom plants to date. These findings illustrate that during the relativelybrief springtime flowering period, floral emissions constitute by far themost significant contribution to the BVOC flux from these tree species, someof which are leafless at this time. Experimental results were integrated intothe MEGAN biogenic emission model and simulations were performed to estimatethe contribution of floral BVOC emissions to the total urban BVOC flux duringthe spring flowering period. The floral BVOC emitted during thisthree-month simulation are equivalent to 11% of the integratedmonoterpene flux for the Boulder urban area.

[学科分类] 地球化学与岩石