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Date of Award
Doctor of Philosophy in Environmental Engineering (PhD)
College, School or Department Name
Department of Geological and Mining Engineering and Sciences
Aerosol and ozone are important components of the atmosphere, which play essential roles in affecting air quality and climate as well as adversely impacting human health. In this work, a chemical transport model (GEOS-Chem) is used as a tool to improve our understanding of these two species in response to anthropogenic perturbations in the context of global change.
A new physical condensation-coagulation and chemical oxidation aging scheme for carbonaceous aerosols has been implemented in GEOS-Chem. Atmospheric parameters, including water vapor, ozone, hydroxyl radicals and sulfuric acid concentrations, affect the hydrophobic-to-hydrophilic conversion lifetime (τ) for carbonaceous aerosols. The updated τ shows large spatial and temporal variations with the global average calculated to be about 2.6 days (up to 11 km altitude). Compared to the control simulation, the updated aging scheme increases the global burdens of BC (OC) by 9% (3%). Considerable enhancements of carbonaceous aerosols are observed in the Southern Hemisphere. Additionally, the updated aging scheme improves model simulations of carbonaceous aerosols for the remote areas in the Northern Hemisphere revealed from the comparisons to multiple observational datasets.
The impacts of land use/land cover associated with global change on global wildfires over the period 2000-2050 are investigated. Compared to the 2000 levels, the 2050 fire frequencies are projected to increase by about 27%. Changes in fire meteorology (including temperature, precipitation and relative humidity) driven by 2000-2050 climate change are calculated to increase the global fire frequency by approximately 19%. Relative to the present-day conditions, fire frequencies under the 2050 conditions are found to increase by 4% in response to changes in lightning activities driven by climate change. Changes in land cover by 2050 driven by climate change and increasing CO2 fertilization are expected to increase the global wildfire occurrences by 15% relative to the 2000 conditions while the 2000-2050 anthropogenic land use changes show little effects on global wildfire frequency. The 2000-2050 changes in global population are projected to reduce the total wildfires by about 7%.
Model evaluations against in-situ measurements and balloon campaigns over Summit, Greenland in the Arctic show that snowpack NOx emissions missing from current model contribute over 50% to the model simulated surface NOx mixing ratios during late spring to early summer. Simultaneously, model simulated surface ozone mixing ratios during this period are found to be underestimated by ~9 ppbv (19%), which possibly attributes to the missing snowpack NOx emissions in the model, model uncertainties in assimilated meteorological fields as well as the underestimates of stratosphere-to-troposphere events during this period.
Driven by intensification of agricultural fertilizer applications in the sub-Saharan Africa, future African surface soil NOx emissions are projected to substantially increase. Constrained by field measurements, model simulation by GEOS-Chem shows that surface ozone mixing ratios increase by up to 2.2 ppbv in response to the 150 kg N ha-1 fertilizer application rate, which potentially causes about 2-2.5% yield decline for crop productions.
Huang, Yaoxian, "GLOBAL MODELING OF ATMOSPHERIC OZONE AND AEROSOLS: MODEL IMPROVEMENTS AND APPLICATIONS", Dissertation, Michigan Technological University, 2014.