Abstract. In this study we look at the concentration of CO at four remote stations in the North Pacific to evaluate the impact of Asian industrial emissions on the remote atmosphere. Using a locally weighted smoothing technique to identify individual data outliers from the seasonal cycle, we have identified 22-92 outliers or "events" (greater than 5 ppbv above the seasonal cycle) at each site for the 3-6 year data records. Using isentropic back trajectories, we identify a possible source region for each event and present a distribution of the trajectory types. For the events at Midway, Mauna Loa, Guam, and Shemya, we are able to identify a source region for the elevated CO in 82, 72, 65, and 50% of the events, respectively. At Mauna Loa and Midway a majority of the events occur during spring and are usually associated with transport from Asia. These events bring the highest CO mixing ratios observed at any time during the year to these sites, with CO enhancements up to 46 ppb. At Guam, easterly trade winds are the norm, but occasionally synoptic events bring Asian emissions to the island, generally during late summer and fall, from either East Asia or Southeast Asia (e.g., Indonesia). These events bring with them the largest CO enhancements of any of the four sites considered in this paper, up to 58 ppb. Finally, to examine the robustness of our conclusions, we redo our analysis using the more stringent definition that an event must be either 10 or 15 ppb above the seasonal cycle. Although this reduces the number of events identified at each site, it does not significantly change the fraction of events which can be attributed to a known source.

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. In situ measurements of surface CO were conducted from June 1994 to May 1995, and surface ozone was measured from February to May, 1995, at Shemya, Alaska (52o44'N, 174o06'E) using nondispersive infrared-gas filter correlation (GFC) and UV absorption spectroscopy, respectively. Over the same period, air samples were collected in flasks for analysis of CO and other trace gases as part of the NOAA-CMDL cooperative air sampling network. We compared the continuous GFC measurements with the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory (NOAA-CMDL) flask data. Over this 1-year period, CO mixing ratios varied between 60 and 250 parts per billion by volume (ppbv). Within this range, the comparison between the two measurements is quite good, with an overall R 2 of 0.953 and an average difference of 3.1%. A seasonal cycle is apparent in the CO data, with a springtime maximum and a summer minimum. Synoptic influences on the data include transport from the lower-latitude Pacific, bringing air with very low CO mixing ratios to Shemya, and, occasionally, transport from industrial areas in east Asia, including northern China, Japan, and eastern Russia. A scatterplot of CO versus 03 using all the data shows essentially no relationship at this remote site. This result implies that the primary sources and sinks for these trace gases are different at this location. However, during a few 12-to 48-hour periods in fall and late spring, enhancements in CO or in both CO and 03 were observed. During these periods, isentropic back trajectories indicate transport from the west and southwest. However, the trajectories are often difficult to interpret due to looping and are of short duration due to impact at the surface. These complexities are associated with the presence of cyclonic systems in the region. The local meteorological data suggest that the enhanced concentrations occurred around the time when these cyclonic systems passed near the sampling site. Synoptic surface pressure maps indicate that these cyclonic systems formed or crossed industrial regions in east Asia and passed near Shemya on their way to the Bering Sea. This process suggests a role for transport of anthropogenic pollutants by cyclonic systems moving northward along the western edge of the Pacific Ocean.

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