자료유형  

 학위논문

Control Number  

0017161434

International Standard Book Number  

9798382775982

Dewey Decimal Classification Number  

551.5

Main Entry-Personal Name  

Li, Yaowei.

Publication, Distribution, etc. (Imprint  

[S.l.] : Harvard University., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

167 p.

General Note  

Source: Dissertations Abstracts International, Volume: 85-12, Section: B.

General Note  

Advisor: Keutsch, Frank.

Dissertation Note  

Thesis (Ph.D.)--Harvard University, 2024.

Summary, Etc.  

요약The interactions between atmospheric aerosols and radiation represent one of the largest uncertainties in our scientific understanding of climate change. Aerosols in the stratosphere and upper troposphere (S/UT), above approximately 7 km from the Earth's surface, play a critical role in modulating global radiative balance by scattering and absorbing radiation, and by affecting the lifecycle of ice clouds. Stratospheric aerosols have been suggested to contribute to ~21% of the total aerosol direct radiative forcing since 1850. Furthermore, they affect the protective ozone layer directly by modulating heterogeneous reaction rates of halogen activation and N2O5 hydrolysis and indirectly via more uncertain radiative impacts on temperature and dynamics. This thesis delves into novel insights regarding the microphysical, chemical, and optical properties of S/UT aerosols, which are essential for understanding their radiative and chemical effects. Despite significant advances, important questions remain about these properties, especially in light of intermittent aerosol perturbations from volcanic eruptions and severe wildfire/biomass burning events.A primary focus of this thesis lies in unraveling the diverse chemical composition and morphology of S/UT aerosols and its influence on their optical properties, consequently affecting radiative forcing. Contrary to the traditional assumption that stratospheric aerosols are predominantly composed of sulfate, observations and recent modeling studies indicate that organic matter may constitute a substantial portion (5-60%) of the particle mass in the lower stratosphere. The implications of these organic components are not fully understood but could lead to substantial revisions in our comprehension of the stratosphere's climate influence. This thesis begins by exploring the composition dependence of stratospheric aerosol radiative forcing, particularly examining the sensitivity to the intrinsic optical property (i.e., refractive index) of organics and their mixing states with sulfates. Using long-term balloon-borne aerosol measurement records and radiative transfer calculations, this work revealed that organics may have significant impacts (up to a 100% change) on stratospheric aerosol shortwave radiative forcing during periods of minimal to moderate volcanic activity (Chapter 1). However, data on the refractive index of stratospheric organic aerosols is scarce. To bridge this gap, laboratory measurements of the refractive index of organic aerosols were conducted, alongside the development of a semi-empirical model that predicts the refractive index of organic aerosol from its widely measured oxygen-to-carbon and hydrogen-to-carbon elemental ratios (Chapter 2). These efforts help better constrain the optical properties of organic-containing stratospheric aerosols.The second focus of this thesis involves in situ sampling and measurements of aerosols in the S/UT. During the NASA DCOTSS (ER-2 aircraft) and NOAA SABRE (WB-57 aircraft) missions, I developed and deployed two aircraft instruments to: 1) measure S/UT aerosol concentration and size distribution across a range of 140-2,500 nm in diameter, and 2) collect S/UT aerosol samples for offline chemical composition and morphology analysis (Chapter 3). My work yielded a valuable dataset of aerosol concentration, size distribution, composition, and morphology up to 22 km over North America. This dataset is essential for characterizing the baseline state of S/UT aerosols and discerning the effects of volcanic and wildfire perturbations.Notably, volcanic plumes from La Soufriere eruptions in April 2021 were sampled repeatedly in the stratosphere, enabling detailed analysis of aerosol concentration and size distribution within these volcanic plumes and their spatiotemporal evolutions in the stratosphere. Contrary to the conventional wisdom that volcanic eruptions lead to increased aerosol size-evidenced by the aftermath of massive events like the 1991 Pinatubo eruption-my findings from the 2021 La Soufriere eruption indicate a decrease in aerosol effective diameter within the midlatitude lower stratosphere due to a significant increase in small particles ( 400 nm). This suggests a nuanced impact of relatively smaller yet more frequent eruptions. The radiative and ozone impacts of these volcanic plumes were further examined using the SOCOL-AERv2 aerosol-chemistry-climate model (Chapter 4).Additionally, encounters with wildfire smoke from a pyrocumulonimbus (pyroCb) event were recorded in the UT. These pyroCb smoke aerosols show a distinct large size mode (500-600 nm diameter) and a high concentration of biomass burning organics. The radiative effects of these large smoke aerosols were assessed using radiative transfer calculations. Subsequent offline analysis of the S/UT aerosol samples unveiled the prevalence of organic-containing particles, particularly those originating from biomass burning sources, in the summer stratosphere. These particles were predominantly complex mixtures of inorganic and organic substances, occasionally intermingled with black carbon (Chapter 5).My Ph.D. work integrates fieldwork, laboratory experiments, instrumentation, and computational modeling to delve into the properties, perturbations, and radiative effects of aerosols in the S/UT. This multifaceted approach aids in quantifying the climate and chemical impacts of S/UT aerosols and underscores the imperative to increase our understanding of organic and biomass burning aerosols in this region.

Subject Added Entry-Topical Term  

Atmospheric chemistry.

Subject Added Entry-Topical Term  

Climate change.

Subject Added Entry-Topical Term  

Environmental science.

Subject Added Entry-Topical Term  

Meteorology.

Index Term-Uncontrolled  

Aerosols

Index Term-Uncontrolled  

Airborne measurements

Index Term-Uncontrolled  

Microphysical properties

Index Term-Uncontrolled  

Optical properties

Index Term-Uncontrolled  

Radiative forcing

Index Term-Uncontrolled  

Stratosphere

Index Term-Uncontrolled  

Upper troposphere

Added Entry-Corporate Name  

Harvard University Engineering and Applied Sciences - Engineering Sciences

Host Item Entry  

Dissertations Abstracts International. 85-12B.

Electronic Location and Access  

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Control Number  

joongbu:658298