Carbon monoxide (CO) and ethane (C2H6) trends from ground-based solar FTIR measurements at six European stations, comparison and sensitivity analysis with the EMEP model.

Trends in the CO and C₂H₆ partial columns (~0-15 km) have been estimated from four European ground-based solar FTIR (Fourier Transform InfraRed) stations for the 1996-2006 time period. The CO trends from the four stations Jungfraujoch, Zugspitze, Harestua and Kiruna have been estimated to -0.45±0.16% yr^-1, -1.00±0.24% yr^-1, -0.62±0.19% yr^-1 and -0.61±0.16% yr^-1, respectively. The corresponding trends for C₂H₆ are -1.51±0.23% yr^-1, -2.11±0.30% yr^-1, -1.09±0.25% yr^-1 and -1.14±0.18% yr^-1. All trends are presented with their 2-σ confidence intervals. To find possible reasons for the CO trends, the global-scale EMEP MSC-W chemical transport model has been used in a series of sensitivity scenarios. It is shown that the trends are consistent with the combination of a 20% decrease in the anthropogenic CO emissions seen in Europe and North America during the 1996-2006 period and a 20 % increase in the anthropogenic CO emissions in East Asia, during the same time period. The possible impacts of CH₄ and biogenic volatile organic compounds (BVOCs) are also considered. The European and global-scale EMEP models have been evaluated against the measured CO and C₂H₆ partial columns from Jungfraujoch, Zugspitze, Bremen, Harestua, Kiruna and Ny-Ålesund. The European model reproduces, on average the measurements at the different sites fairly well and within 10-22% deviation for CO and 14-31% deviation tor C₂H₆. Their seasonal amplitude is captured within 6-35% and 9-124% for CO and C₂H₆, respectively. However, 61-98% of the CO and C₂H₆ partial columns in the European model are shown to arise from the boundary conditions, making the global-scale model a more suitable alternative when modeling these two species. In the evaluation of the global model the average partial columns for 2006 are shown to be within 1-9% and 37-50% of the measurements for CO and C₂H₆, respectively. The global model sensitivity for assumptions made in this paper is also analyzed. [ABSTRACT FROM AUTHOR]