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

Abstract. Trends in the CO andC₂H₆ 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 for 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.