[Eoas-seminar] Meteorology PhD Defense for Jason Ducker, November 4, 1:00 PM, Love 353

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Mon Oct 28 10:09:41 EDT 2019

Meteorology Seminar

Jason Ducker

PhD Meteorology Candidate

Title:  Developing new datasets to evaluate tropospheric photochemistry and the effects of ozone uptake in the biosphere

Major Professor:  Dr. Christopher Holmes

Date: November 4, 2019                        Time: 1:00 PM

Location: Werner A. Baum Seminar Room (353 Love Building)
(Please join us for refreshments served outside room 353 Love @ 12:30 PM)

In the presence of water vapor, photolysis of tropospheric ozone (O3) produces the hydroxyl radical (OH), which is a strong oxidant that directly and indirectly controls a host of greenhouse gases and air pollutants. When tropospheric O3 reaches the surface, its oxidative effects perturb plant transpiration and photosynthesis. Although these effects have been included in climate and air quality models, there are limited observational datasets to constrain key aspects of atmospheric photochemistry and O3 deposition on regional to global scales. This dissertation develops and uses two new datasets to better understand the ozone photochemistry and impacts.
Photolysis, the breaking of chemical bonds by sunlight, is the engine for reactive atmospheric chemistry. It controls production of atmopsheric oxidants, especially O3 and OH, which then influence the lifetimes of other air pollutants and climate forcing agents. Global chemistry and climate models differ in their estimates of these photolysis rates and there hasnt been datasets capable of discriminating amongst different models. Here, we integrate satellite-retrivals of clouds and aerosols into a photolysis code and produce a 3-D global photolysis dataset called Sat-J. We show that Sat-J is tightly correlated with in-situ measurements of photolysis rates from airborne chemistry campaigns, with errors (4-20%) mainly attributed to differences in cloud sampling and surface albedo characteristics. By comparing regional, not necessarily collocated, averages of aircraft data, SatJ, and a chemistry model (GEOS-Chem); we demonstrate that SatJ provides a representative climatology of photolysis rates across the globe and can serve as a benchmark for photochemistry models.
Using surface micrometeorological fluxes and surface O3 monitoring networks, we also develop and evaluate a method to estimate O3 deposition and stomatal O3 uptake across networks of eddy covariance flux tower sites where O3 concentrations and O3 fluxes have not been measured. This method, called SynFlux, reproduces the variability in daily stomatal O3 uptake at sites with O3 flux measurements, with a modest bias (21% or less) attributed to gridded O3 concentrations. Across SynFlux sites, we highlight environmental factors controlling spatial patterns in O3 deposition and showed that previous O3 concentration-based metrics for plant damages did not correlate with SynFlux O3 uptake, which is a better predictor for plant damage than ambient concentration in air.
SynFlux has dramatically expanded the available data on surface O3 deposition, which can now be used for performing ecosystem impact studies across a species and climates in the US and Europe. Past controlled experiments involving single plant species have shown that O3 uptake can degrade water-use efficiency (WUE), which is the ratio of carbon uptake in photosynthesis (GPP) to water loss in plant transpiration (T). Using SynFlux sites, we can quantify this effect for whole ecosystems under natural environmental variability, which has not been previously studied. Across 74 SynFlux sites, we find a significant negative relationship (-0.02% per [cid:image001.png at 01D58D77.CFC4BF20] mol m-2 d-1) between daily cumulative O3 uptake (CUO) and WUE anomalies, with the largest impacts occurring at forest sites. Past controlled studies of selected individual species also observed a similar O3 reduction of WUE over the growing season, indicating a consistent response to O3 across multiple species with an ecosystem. When we analyze the relationships between daily CUO and GPP or T anomalies, we also find that CUO degrades GPP and increases T over the growing season. We postulate that O3 degrades WUE through O3 non-stomatal biochemical factors, which result in a reduction of GPP or an increase in T. Our SynFlux results here provide climate models the ability to incorporate O3-dose response relationships between O3 uptake and ecosystem carbon and water vapor fluxes across ecosystems that have not previously been studied.

Shel McGuire
Florida State University
Academic Program Specialist
Department of Earth, Ocean, & Atmospheric Science
1017 Academic Way, 410 Love Building (Meteorology)
Tallahassee, FL 32306

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