Date of Award

Spring 2026

Language

English

Embargo Period

4-30-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Atmospheric and Environmental Sciences

Program

Atmospheric Science

First Advisor

Cheng-Hsuan Lu

Committee Members

Fangqun Yu, Oliver Timm, Xueying Yu

Keywords

Aerosols, PyroCb, Wildfires

Subject Categories

Atmospheric Sciences | Atomic, Molecular and Optical Physics | Climate

Abstract

Stratospheric aerosols play an important role in maintaining global radiative balance with impacts to stratospheric equilibria through physical and chemical forcings.  Stratospheric aerosol size distributions, in particular aerosol size, are vitally important in determining the physical and chemical impacts of aerosols in the stratosphere. The representation of aerosol size and size distributions in most climate models contain large uncertainties due to relatively sparse sampling of stratospheric aerosols. Occultation measurements from satellite provide an unique opportunity to retrieve the aerosol size distribution using high quality aerosol extinction measurements. A retrieval algorithm is developed to characterize size distributions of stratospheric aerosols from global utilities like SAGEIII/ISS, NASA’s contemporary occultation measuring instrument sampling the stratosphere.

The recent two decades have seen an increase in awareness of mega wildfires which produce pyrocumulonimbus (pyroCb), smoke filled thunderstorms which efficiently transport smoke and gas into the upper troposphere and lower stratosphere (UTLS). Smoke aerosols are distinct in their chemical, optical, and microphysical properties from stratospheric sulfate aerosols. The role of pyroCb events in altering stratospheric equilibria through changes in stratospheric aerosol concentrations, composition, and size distributions is a critical topic of ongoing study, given the trend of more intense, and longer wildfire seasons and increased pyroCb formations globally. Sparse measurements of UTLS aerosols means that there is significant uncertainty regarding the initial size distribution and composition of pyroCb aerosols, as well as how their optical and microphysical properties evolve following such events. Constraining the aerosol size distributions in the lower stratosphere can help to address these uncertainties in global modeling and instrumental and algorithmic development efforts.

Aerosol size distribution retrievals are shown to validate well in both test and applied settings under background, moderate, and enhanced aerosol scenarios. The satellite retrieved aerosol size distributions compare favorably with in situ samples and provides insight into the vertically distributed aerosol field and aerosol optical and microphysical properties. Aerosol size distributions are shown to match the range of the in situ measurements and are composed of ultrafine, fine, and coarse mode aerosols with high resolution of the accumulation mode. The retrieval using bimodal lognormal distribution can potentially address limitations of aerosol retrieval using single mode where aerosol size can potentially be inflated or misrepresentative of the total aerosol population in a given sample of air. PyroCb aerosols are shown to be enhanced over boundary layer smoke samples with size distributions mostly containing concentrations within the accumulation mode. Large pyroCb events in terms of aerosol mass in the UTLS concurrently have increased size spanning the upper accumulation mode up to 1–2 μm.

License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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