HR: 10:50h
AN: A21F-03    [PDF]
TI: Large vertical gradients indicate emission, photochemical production, deposition, or a combination for a wide variety of organic trace gases in a Ponderosa Pine plantation in the Sierra Nevada Mountains of California
AU: * Holzinger, R
EM: holzing@nature.berkeley.edu
AF: University of California at Berkeley, ESPM Department 151 Hilgard Hall, Berkeley, CA 94720 United States
AU: Lee, A
EM: alee@nature.berkeley.edu
AF: University of California at Berkeley, ESPM Department 151 Hilgard Hall, Berkeley, CA 94720 United States
AU: Goldstein, A H
EM: ahg@nature.berkeley.edu
AF: University of California at Berkeley, ESPM Department 151 Hilgard Hall, Berkeley, CA 94720 United States
AB: We measured vertical gradients for a wide suite of volatile organic compounds (VOCs) through the forest canopy at the Blodgett Forest Research Station (38.88N, 120.62W, 1315m elevation) during summer 2003 using a PTR-MS. The sampling height was switched between 1.1, 3.1, 4.9, 8.75, and 12.5 m above the ground at 6 minute intervals, and mass to charge ratios ranging from 20 to 205 were recorded. The ability of the PTR-MS to achieve high time resolution, low detection limits (few ppt for averaged data), and whole air measurements without preconcentration allowed us to measure gradients for compounds that cannot be measured easily with other techniques. Significant gradients were observed for many compounds. Monoterpene and sesquiterpene emissions from the plants caused mixing ratios that were typically 2-3 times higher below the canopy than above, and our data did not show evidence for soil deposition of these compounds. Methanol mixing ratios were highest at the lowest level (1.1m) indicating that much of the methanol is released from or near the soil. Gradients with the highest mixing ratio above the forest and lowest near the ground indicated persistent deposition for mass 42 (acetonitrile) and mass 71 (MVK+MACR); compounds that are predominantly transported to the local ecosystem. Mixing ratios of several compounds were highest at levels within the canopy and significantly lower above and below. This pattern is indicative of compounds that are emitted or photochemically produced in the canopy whose photochemical lifetime is so short that they are removed before being mixed down to the ground (few minutes) and/or they are efficiently deposited to the soil. Many of these compounds were so far identified only by their mass to charge ratio and their identity has not been conclusively determined. Concentrations of compounds emitted as a function of light and temperature by Ponderosa Pine tended to be highest at the 3.1m level during the day; thereby showing that the emission rates were highest around this elevation; among those compounds is MBO. For one week every month we measured direct plant emissions with a branch enclosure in order to determine which compounds were emitted directly from the plants and which were photochemically produced.
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting