UC Irvine

This dissertation involves measurements of ethane and carbon monoxide in the air trapped in polar firn (porous ice) and ice cores from Greenland and Antarctica. Ethane and carbon monoxide are reactive trace gases that are involved in tropospheric ozone formation and impact the atmosphere's oxidative capacity. The major sources of these gases are from anthropogenic fossil fuel use, biofuel use, and biomass burning. Ethane fossil fuel emissions are mainly from evaporative emissions associated with the production, processing and transmission of fossil fuels. Carbon monoxide emissions are primarily due to fossil fuel combustion and atmospheric hydrocarbon oxidation. In this study, past atmospheric levels of ethane and carbon monoxide are reconstructed from polar firn air to examine man's impact on their global budgets.

Antarctic and Greenland firn air measurements show that ethane levels rose globally during the twentieth century, reached a peak in the 1980s, followed by a decline to their present-day levels. Ethane emissions reconstructions suggest that the ethane decline since 1980 was likely due to a reduction in fossil fuel emissions. The firn-air based ethane emissions histories suggest the slowdown in the atmospheric methane growth rate during the 1980s and 1990s was also due to reductions in fossil fuel emissions, possibly as a result of capture, recovery, and/or storage of natural gas that was previously vented or flared. In order to develop longer atmospheric histories, ethane was analyzed in air extracted from bubbles in Antarctic ice cores. Both dry extraction and wet extraction procedures were utilized in this study. The results indicate that preindustrial (1000-1900 AD) ethane levels over Antarctica were 40-50% lower than today.

Carbon monoxide levels increased by roughly 40% from 1920-1980, with near zero growth after the 1990s, based on the South Pole firn air reconstructions. The rate of CO rise during the mid-twentieth century was faster than the rate of methane rise during the same period. Modeling studies show that the twentieth century CO trends at high latitudes in each hemisphere can be explained by changes in anthropogenic fossil fuel emissions. The timing of the peak and decline in the anthropogenic CO emissions reconstructions is consistent with the implementation of clean air policies in the US and Europe.