| Summary: | We present long-term (5-year) measurements of particulate matter (PM10), elemental carbon (EC), organic carbon (OC), and water-soluble organic carbon (WSOC) in aerosol filter samples with an upper limit of ~ 10 µm collected at the Zotino Tall Tower Observatory in the middle-taiga subzone (Siberia). The data are complemented with carbon monoxide (CO) measurements. Air mass back trajectory analysis and satellite image analysis were used to characterize potential source regions and the transport pathway of haze plumes. Polluted and background periods were selected using a non-parametric statistical approach and analyzed separately. In addition, near-pristine air masses were selected based on their EC concentrations being below the detection limit of our thermal/optical instrument. Over the entire sampling campaign, 75 % and 48 % of air masses in winter and in summer, respectively, and 42 % in spring and fall are classified as polluted. In the winter season, pollution plumes originated mainly from the big industrialized cities to the south and southwest of the site. During the winter pollution events, the pollution concentration enhancements (Δ values) ratios ∆OC / ∆EC and ∆EC / ∆CO are 3.9 ± 0.6 and 5.8 ± 0.7 ng m−3 ppb−1, respectively, suggesting that the contribution of coal and other fossil fuel burning for heating was dominant. In summertime, pollution plumes arrived at the ZOTTO site from nearby large-scale boreal wildfires, which were observed during the three years from 2011 to 2013. As a result, the seasonal concentrations of CO, PM10, and OC were as high as 670 ± 710 ppb, 59 ± 53 µg m−3, and 26 ± 27 µg m−3, respectively, with ∆OC / ∆EC of 26.2 ± 0.1 and ∆EC / ∆CO of 1.3 ± 0.1 ng m−3 ppb−1. Agricultural fires from the steppe zone of southern Siberia and northern Kazakhstan also accounted for elevated concentrations of CO and carbonaceous species. For one extreme pollution episode observed on 28 April 2010 the CO, PM10, EC, and OC concentrations were as high as 261 ± 12 ppb, 54.4 ± 3.7, 1.5 ± 0.3, and 18.9 ± ...
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