Investigating Tropospheric Hydrogen Peroxide Trends from 1950-2014
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sun-sunv-sm-eaps-2024-thesis.pdf
Description
Thesis PDF
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10.36 MB
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Adobe PDF
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Author(s)
Sun, Vanessa
Advisor(s)
Fiore, Arlene
Date Issued
May 2024
Publisher
Massachusetts Institute of Technology
Abstract
The oxidizing capacity of the atmosphere, or the ability of the atmosphere to clean itself of the pollutants that build up in the troposphere, is determined by oxidants including ozone (O₃), HOx radicals (OH and HO₂) and hydrogen peroxide (H₂O₂). O₃ is the primary source for HOx radicals, while H₂O₂ is a key sink for HOx radicals that terminates the rapid cycling between OH and HO₂. The concentrations of the HOx radicals and H₂O₂ are difficult to measure directly, with scarce long term data of H₂O₂ primarily available through ice core records. Given the lack of observational data, much of our knowledge on the history of tropospheric oxidants relies on modeling studies. We quantify the global H₂O₂ burden and trends between 1950 and 2014 from the Community Earth System Model - Whole Atmosphere Community Climate Model version 6 (CESM2-WACCM6). This is a global chemistry-climate model, with each of the 13 ensemble members simulating the historical period. Each has a miniscule difference in their initial conditions, and subsequently yield different responses when reacting to the same external forcing. In this study, we discern where H₂O₂ is increasing in the troposphere, particularly in the Southern Hemisphere and over Antarctica. We quantify a rate of increase for the H₂O₂ annual burden, noting the rise beginning in the 1970's and growing from 14% in the 1970's to 34% in the 2000's, with respect to the burden in the 1950's. We find that changes in globally averaged annual mean H₂O₂ are most strongly correlated with changes in ozone, whereas over Antarctica, the strongest relationships for H₂O₂ trends occur with ozone photolysis rates. This aligns well with previous ice core and modelling studies in the literature. Lastly, we also find evidence of stratospheric ozone depletion having no discernible impact on global H₂O₂ burden changes using an additional parallel set of simulations holding ozone depleting substances at 1950 levels.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
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