The Isotopes of Carbon Monoxide in the Free Troposphere and Their Implications to Atmospheric Chemistry.

My thesis project was designed to provide information for answering the following questions: what is the oxidative capacity of the troposphere, and how are the source strengths of carbon monoxide partitioned? Because of its active role in tropospheric chemistry, carbon monoxide is important in determining the fate of a number of species, including hydroxyl radicals. OH is responsible for the oxidation of most hydrocarbons and many other reduced trace gas species, including carbon monoxide. ^{14} CO in atmospheric CO serves as a natural tracer for its destruction, as the source function can be well constrained. By determining the tropospheric inventory of ^{14}CO and calculating its source strength, one may realize the rate of destruction. Similarly, because certain sources have unique stable isotope signatures, an analysis of the stable isotopes provides information on the relative strengths of those sources. This enables the partitioning of anthropogenic sources (such as biomass burning and fossil fuel combustion) from natural pathways (e.g., hydrocarbon oxidation). The airborne sampling system which has been built for the collection of large (1000 liters) air samples is discussed, with particular attention given to the modifications necessary to ensure the integrity of the samples. The methodology for extraction and analysis of carbon monoxide is also discussed. ^{14}CO, ^{13}CO, C^ {18}O, and CO concentration results are presented and interpreted. For the ^{14 }CO data, a two dimensional transport model has been used to help relate ^{14} CO to OH. Based on this analysis there exists a possibility of a sink for carbon monoxide which may be as large as 35% of the presently known sink strength. The stable isotopes are used to constrain the relative contributions from various sources between the two hemispheres.