Continuous measurements of O3 and CO were made during 1997--1999 at Mondy, a remote mountain site in East Siberia, in order to quantify their mixing ratios and their climatology in the background troposphere of continental Eurasia. The seasonal cycles of O3 and CO show the spring maximum-summer minimum similar to that previously reported in the remote Northern Hemisphere. The influences of Siberian forest fires on the variations of CO mixing ratios at Mondy were observed both on a local and a regional scale during spring 1997 and fall 1998, respectively. We further evaluate the possible impact of European pollution export to the remote atmosphere of Siberia using trajectory analysis. It was found that the O3 and CO mixing ratios in the air masses transported from Europe are higher than those from Siberia and high-latitude regions for most of the year. The medians of O3 and CO mixing ratios associated with the European air masses are 44.2 and 134 ppb, respectively, in comparison with 42.7 and 128 ppb in the Siberian air masses, and 41.0 and 110 ppb in the high-latitude air masses. The residence time analysis of air masses transported from the European continent indicates that CO mixing ratios significantly decrease with longer transport time of air masses from Europe, while rapid air motion retains higher CO mixing ratios in every season due to the admixture of polluted European air into the continental background air during air mass transport over Eurasia and photochemical loss by OH. Because of a shorter lifetime in summer, CO mixing ratios decrease at a rate of 6--7 ppb per day, while they decrease at a rate of 2--4 ppb per day in winter and spring. The similar trend is found for O3 but only in summer, at a rate of 2--3 ppb per day. From this analysis, we are able to identify that European pollution exerts an influence, though not very strong, on the background O3 and CO at Mondy in remote Siberia/East Asia.