Trend Analysis and Model Comparison of Ground-Based Solar FTIR Data

Licentiatavhandling, 2011

The Network for the Detection of Atmospheric Composition Change (NDACC) was initiated in the early 90s to investigate the major atmospheric problem of the day, the destruction of stratospheric ozone. About three years later solar FTIR measurements were started in Harestua, 50 km north of the Norwegian capital Oslo. Since then, much of the medial focus has shifted towards the climate issue but still the stratospheric chemistry is of great importance. Since the FTIR measurements in Harestua, and at several other stations within the NDACC network, have been going on for more than 15 years it is now possible and of great interest to study the long term trends of the measured species. In this thesis, the measured time series of methane (CH4) and nitrous oxide (N2O) have been studied. Reasons for the variability in these two important climate gases were outlined and used in a multiple regression model to estimate reliable long term linear trends. Further, the trend model was used on FTIR data from four European FTIR stations to investigate spatial difference in the trends. A very useful tool in atmospheric science is chemical transport models (CTMs). In this thesis, the EMEP model was used to find possible causes to the negative trends in carbon monoxide (CO) seen within the NDACC network. CO is the dominant sink for the hydroxyl radical (OH) which acts as a detergent of the atmosphere and hence is a key component of the tropospheric chemistry.