Atmospheric sulfur sources and chemistry from preindustrial to present

Abstract

Atmospheric aerosols affect climate by scattering radiation and influencing cloud properties. Sulfate aerosols are estimated to have a large but uncertain cooling effect on global climate over the industrial era. A substantial portion of this uncertainty is caused by the dependence of anthropogenic aerosol radiative forcing on the preindustrial (natural) aerosol abundance due to the nonlinear relationship between aerosol abundance and cloud albedo. This nonlinear relationship motivates study of the relative importance of sulfate sources, sulfur oxidation chemistry, and how sulfate aerosols change over time. In this dissertation, I investigate the sources and chemistry of sulfate aerosols over the industrial era using ice core records of the sulfur isotopic composition of sulfate. Chapter 1 provides background and motivation for the research questions explored in this dissertation. Chapter 2 quantifies anthropogenic influence on Greenland sulfate using sulfur isotopes in a Summit, Greenland ice core. Chapter 3 shows that a change in DMS oxidation chemistry in regions influenced by anthropogenic pollution causes an industrial-era decline in methanesulfonic acid and an increase in biogenic sulfate in a Greenland ice core. Chapter 4 compares industrial-era changes in ice core MSA and biogenic sulfate to trends in changes in DMS oxidation chemistry simulated in a global model. Chapter 5 examines sulfate sources in the southern high latitudes, which are quantified using sulfur isotopes in Antarctic ice cores and compared to a global model. Conclusions and opportunities for future work are summarized in Chapter 6.