Abstract. The isotopic composition of carbon monoxide (•3C,

Abstract. The northern Eurasian regions and Arctic Ocean will very likely undergo substantial changes during the next decades. The Arctic-boreal natural environments play a crucial role in the global climate via albedo change, carbon sources and sinks as well as atmospheric aerosol production from biogenic volatile organic compounds. Furthermore, it is expected that global trade activities, demographic movement, and use of natural resources will be increasing in the Arctic regions. There is a need for a novel research approach, which not only identifies and tackles the relevant multi-disciplinary research questions, but also is able to make a holistic system analysis of the expected feedbacks. In this paper, we introduce the research agenda of the Pan-Eurasian Experiment (PEEX), a multi-scale, multi-disciplinary and international program started in 2012 (https://www.atm.helsinki.fi/peex/). PEEX sets a research approach by which large-scale research topics are investigated from a system perspective and which aims to fill the key gaps in our understanding of the feedbacks and interactions between the land-atmosphereaquatic-society continuum in the northern Eurasian region. We introduce here the state of the art for the key topics in the PEEX research agenda and present the future prospects of the research, which we see relevant in this context.

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Abstract. We present the results of a first comparison of the tropospheric NO 2 column amounts derived from the measurements of the Global Ozone Monitoring Experiment (GOME) with the simulated data from a European scale chemistry transport model (CTM) which is distinct from existing global scale CTMs in higher horizontal resolution and more detailed description of the boundary layer processes and emissions. We employ, on the one hand, the newly developed extended version of the CHIMERE CTM, which covers both Western and Eastern Europe, and, on the other hand, the most recent version (Version 2) of GOME measurement based data-products, developed at the University of Bremen. We evaluate our model with the data from ground based monitoring of ozone and verify that it has a sufficiently high level of performance, which is expected for a state-of-theart continental scale CTM. The major focus of the study is on a systematic statistical analysis and a comparison of spatial variability of the tropospheric NO 2 columns simulated with CHIMERE and derived from GOME measurements. The analysis is performed separately for Western and Eastern Europe using the data for summer months of 1997 and 2001. In this way, we obtain useful information on the nature and magnitudes of uncertainties of spatial distributions of the considered data. Specifically, for Western Europe, it is found that the uncertainties of NO 2 columns from GOME and CHIMERE are predominantly of the multiplicative character, and that the mean relative random (multiplicative) errors of the GOME measurement derived and simulated data averaged over the summer seasons considered do not exceed 23% and 32%, respectively. The mean absolute (additive) errors of both kinds of the data are estimated to be less than Correspondence to: I. B. Konovalov (konov@appl.sci-nnov.ru) 3×10 14 mol/cm 2 . In Eastern Europe, the uncertainties have more complex character, and the separation between their multiplicative and additive parts is not sufficiently unambiguous. It is found, however, that the total random errors of NO 2 columns from both GOME and CHIMERE over Eastern Europe are not, on the average, larger than the errors of the NO 2 columns with similar magnitudes over Western Europe.

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