Records of delta-carbon-13, delta-oxygen-18 and concentration of atmospheric carbon monoxide in the past

Atmospheric carbon monoxide (CO) plays a significant role in atmospheric chemistry, as CO is a major sink for atmospheric hydroxyl radicals (OH) and thus strongly influences the oxidizing capacity of the atmosphere. In this thesis, new high precision measurements of atmospheric CO concentration and isotope composition during the past 700 years have been accomplished by analyzing the air in polar snow and ice.The first part of this study focuses on the trends of atmospheric CO over the past several decades. Firn air samples from the North Greenland Ice Core Project, Berkner Island, and North Greenland Eemian Ice Drilling (NEEM) have been analyzed to reconstruct atmospheric CO concentration and isotopic compositions during the past half century in both hemispheres. Firn diffusion models have been applied for NEEM firn air data to reconstruct past atmospheric trend in CO, indicating that the maximum of CO concentration and delta 18O in high latitude Northern Hemisphere occurred in 1970s-1980s, reflecting the largest contribution of CO emissions from fossil fuel combustion in this time.The second part of this study focuses on atmospheric CO records over the past 700 years. New decade-scale records of CO concentration as well as isotopic ratios have been produced from 40 Antarctic ice core samples (D47 and South Pole). CO concentration in the 13th century was &sim50 ppbv, which is comparable with today's CO level in high-latitude Southern Hemisphere. CO level then gradually dropped to 38 ppbv during the following 300 years, followed by a gradual increase to 55 ppbv in 1900. delta 13C and delta18O decreased by about 3&permil and 5&permil respectively from 1380 to 1700, then increased by about 3&permil and 5&permil respectively by 1900. Mass balance model implies biomass burning emissions were high in the 13th century, but reduced by &sim50% over the next 300 years and then almost doubled by 1900. We conclude biomass burning strongly modulated the CO budget during preindustrial time and considerably decreased since the early 20th century. This decrease was nearly compensated by the concomitant CH4 increase, bringing back CO mixing ratio close to its maximum level observed over the last 700 years.