Abstract

Ambient aerosols affect climate and air quality in the Earth system. Global chemical transport models used to study these impacts require an accurate representation of aerosols in terms of shape, composition, and vertical distribution. For example, despite having a complex morphology, mineral dust is often treated as spherical particles in these models. This can lead to errors in optical properties calculations, trace gas retrievals, and heterogeneous chemistry. Similarly, inaccurate representation of the vertical distribution of smoke particles in these models can lead to uncertainties in air quality assessments. Aerosol composition also plays a critical role in determining radiative forcing and atmospheric visibility. This dissertation addresses these challenges by developing improved aerosol representations within the GEOS-Chem global chemical transport model. Through a combined theoretical and observational framework, this work advances the modeling of ambient aerosols to better reflect their physical and chemical complexity, thereby enhancing our understanding of their climate and air quality impacts. The dissertation includes three studies. The first study aims to use the spheroidal model as an effective dust shape to study how the optical properties, such as extinction efficiency and phase function, deviate from the previously assumed spherical shape. Subsequently, the study examines how the updated optical properties affect the scattering weights and air mass factor (AMF) used for NO2 retrievals over the urban city of Riyadh. The impact of shape and surface complexities (pores) on dust surface area, reaction, and diffusion parameters is also examined using a theoretical framework based on surface fractal dimension and porosity. The findings emphasize the use of non-sphericity and surface heterogeneity in atmospheric modelling. The second study aims to improve the vertical distribution of smoke aerosols during wildfire events by implementing satellite-constrained plume heights in the high-performance configuration of GEOS-Chem (GCHP). A Gaussian vertical profile is used for aerosol mass distribution, and the resulting satellite-derived surface-level PM2.5 concentrations are compared against ground-based observations. The results demonstrate that incorporating plume height information significantly enhances the accuracy of air quality assessments during wildfire events. The third study focuses on understanding the role of aerosol chemical composition in determining the mass scattering efficiency using measurements from Surface PARTiculate mAtter Network (SPARTAN). The study finds that the hygroscopic species such as secondary inorganic aerosols, organics, and sea salt considerably affect mass scattering efficiency. Sea salt, in particular, emerges as a significant contributor to mass scattering efficiency across all sites. In contrast, mineral dust is not a major contributor even in dust-prone regions. This underscores the important role of relative humidity in particle growth and thereby, in light scattering. Together, these studies provide a more physically grounded and observationally validated framework for representing aerosols in global chemical transport models, leading to improved assessments of their climate and air quality impacts.

Committee Chair

Randall Martin

Committee Members

Jay Turner; Jian Wang; Jun Wang; Rajan Chakrabarty

Degree

Doctor of Philosophy (PhD)

Author's Department

Energy, Environmental & Chemical Engineering

Author's School

McKelvey School of Engineering

Document Type

Dissertation

Date of Award

8-18-2025

Language

English (en)

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