| NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
| Recipient: |
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| Initial Amendment Date: | July 30, 2014 |
| Latest Amendment Date: | August 7, 2015 |
| Award Number: | 1433264 |
| Award Instrument: | Fellowship Award |
| Program Manager: |
Sylvia Edgerton
sedgerto@nsf.gov (703)292-8522 AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
| Start Date: | January 1, 2015 |
| End Date: | December 31, 2016 (Estimated) |
| Total Intended Award Amount: | $86,000.00 |
| Total Awarded Amount to Date: | $172,000.00 |
| Funds Obligated to Date: |
FY 2015 = $86,000.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
Davis CA US 95616-2201 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
Berkeley CA US 94720-8226 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Postdoctoral Fellowships |
| Primary Program Source: |
01001516DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Atmospheric aerosols emitted into the air by biomass burning undergo many chemical reactions in the atmosphere as they age. These reactions can significantly change the impacts that these particles have on air quality and climate. The research conducted by this Postdoctoral Fellow will investigate several factors that can influence these reactions for both simple and complex aerosol mixtures.
The overarching goal of this research is to increase the understanding of heterogeneous OH oxidation mechanisms on organic aerosols by performing laboratory studies on multi-component mixtures of organics (variety of functional groups, and mixtures) and inorganic components (sulfate and nitrate), that more closely mimic the compositional complexity of BBA in the atmosphere. This goal will be achieved by four objectives: (1) Determine the effect multi-functional organic groups have on OH heterogeneous uptake kinetics and oxidation products; (2) Examine whether heterogeneous oxidation of single component organic aerosol systems are different than in mixtures; (3) Determine the effect relative humidity has on single organic systems and mixed inorganic-organic mixtures on heterogeneous reaction mechanisms; and (4) Integrate the data to assess what complexities in model BBA systems have the greatest impact on heterogeneous oxidation mechanisms. The results of this effort will provide useful information to climate modelers in estimating the impact of aerosols on climate change.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Heterogeneous (gas/liquid or gas/solid) reaction rates were measured in "polluted" atmospheres, i.e. in the presence of gas-phase nitric oxide (NO) or gas-phase sulfur dioxide (SO2), on single-component organic aerosol proxies (both liquid or solid) in a specialized reaction chamber designed to mimic atmospheric conditions. The chemical composition of the aerosol was measured using a VUV-photoionization aerosol mass spectrometer at ALS Beamline 9.0.2. The rate of decay of the aerosol was used to quantify the effective uptake coefficient which reveals how fast a reaction occurs. The results show that, as the OH concentration decreases, there is a steep increase in the rate of oxidation of the aerosol.
Because OH quickly reacts with nearby hydrocarbons and oxygen to produce peroxy radicals (RO2, where R is a generic hydrocarbon-based radical), at high concentrations of OH, the concentrations of RO2 will also be relatively high. Thus, at high OH concentrations, RO2 radicals react with other RO2 radicals, which leads to stable products that do not react further. At much lower OH concentrations (approaching atmospheric levels), RO2 reacts primarily with either NO or SO2, which leads to sustained, free-radical chain reactions that result in oxidation rates 10-30 times faster than previsously observed.
These rate measurements, covering four orders of magnitude in OH concentration, overturn the common belief that gas-phase reactions dominate organic aerosol formation and aging and that heterogenous oxidation is simply too slow (on the order of hours) of organic aerosol in urban environments. The incorporation of this new free-radical chain-reaction mechanism into global and regional climate models is expected to improve aerosol mass and composition predictions.
Additional reach was conducted on more complex aerosol systems, such as more dilute aqueous solutions and semi-solids to understand the role of molecular structure on particle phase chain cycling reactions.
Last Modified: 03/30/2017
Modified by: Nicole K Richards
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