A006-0009
Insights into the formaldehyde (HCHO) budget at PROPHET Forest using leaf-level laboratory measurements and the FORCAsT model for biosphere-atmosphere exchange

Monday, 7 December 2020
Poster
Joshua D Shutter1, Joshua L Cox1, Dandan Wei2, Allison L Steiner2, Frank N Keutsch3 and PROPHET-AMOS 2016 Science Team, (1)Harvard University, Department of Chemistry and Chemical Biology, Cambridge, MA, United States, (2)University of Michigan Ann Arbor, Department of Climate and Space Sciences and Engineering, Ann Arbor, MI, United States, (3)Harvard University, School of Engineering and Applied Sciences, Department of Chemistry and Chemical Biology, and Department of Earth and Planetary Sciences, Cambridge, MA, United States
Abstract:
As a ubiquitous oxidation product of volatile organic compounds (VOCs) in the atmosphere, formaldehyde (HCHO) is used by models to help constrain VOC emissions as well as oxidants in the atmosphere. Thus, better constraining the magnitude of HCHO sources and sinks over a forest can aid in our understanding of oxidation processes in these pristine conditions.


Since HCHO exchange with leaves plays a substantial role in the HCHO budget within the crown space of the canopy, leaf-cuvette measurements were conducted on red oak (Quercus rubra) saplings under controlled laboratory conditions to quantify the bidirectional exchange of HCHO. Compensation points on the order of 0.5 – 1 ppbv HCHO were measured with an exponential dependence observed for temperature. This implies that red oak leaves are generally not a source of HCHO within forest canopies. Leaf resistance to HCHO exchange was also parameterized as a function of the leaf’s stomatal conductance to water.


The results of these laboratory measurements were then parameterized in a 1-D forest canopy model (FORCAsT) which was initialized with field measurements of HCHO and other VOCs and oxidants measured at PROPHET Forest during the PROPHET-AMOS 2016 campaign. By constraining the meteorology measured at the site on a photochemically-active day, the FORCAsT model is used to help apportion the HCHO budget throughout the entire height of the forest canopy and determine its exchange between the canopy and the atmosphere.

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