The bi-directional exchange of oxygenated VOCs between a loblolly pine (Pinus taeda) plantation and the atmosphere

[摘要] Using new in-situ field observations of the most abundant oxygenated VOCs(methanol, acetaldehyde, acetone, C₃/C₄ carbonyls, MVK+MAC andacetic acid) we were able to constrain emission and deposition patternsabove and within a loblolly pine (Pinus taeda) plantation with a sweetgum (Liquidambar styraciflua) understory.During the day canopy scale measurements showed significant emission ofmethanol and acetone, while methyl vinyl ketone and methacrolein,acetaldehyde and acetic acid were mainly deposited during the day. Alloxygenated compounds exhibited strong losses during the night that could notbe explained by conventional dry deposition parameterizations. Accompanyingleaf level measurements indicated substantial methanol and acetone emissionsfrom loblolly pine. The exchange of acetaldehyde was more complex.Laboratory measurements made on loblolly pine needles indicated thatacetaldehyde may be either emitted or taken up depending on ambientconcentrations, with the compensation point increasing exponentially withtemperature, and that mature needles tended to emit more acetaldehyde thanyounger needles. Canopy scale measurements suggested mostly deposition.Short-term (approx. 2 h) ozone fumigation in the laboratory had nodetectable impact on post-exposure emissions of methanol and acetone, butdecreased the exchange rates of acetaldehyde. The emission of a variety ofoxygenated compounds (e.g. carbonyls and alcohols) was triggered orsignificantly enhanced during laboratory ozone fumigation experiments. Theseresults suggest that higher ambient ozone levels in the future might enhancethe biogenic contribution of some oxygenated compounds. Those withsufficiently low vapor pressures may potentially influence secondary organicaerosol growth. Compounds recently hypothesized to be primarily produced inthe canopy atmosphere via ozone plus terpenoid-type reactions can alsooriginate from the oxidation reaction of ozone with leaf surfaces and insidethe leaf. This needs to be taken into account when scaling up very reactivebiogenic compounds.

[学科分类] 大气科学