Potentiality of Ozone production over sub-Arctic Boreal forest in Alaska during thawing Period

Ozone is generally decomposed in natural vegetation, however, we found ozone efflux during the beginning of soil thawing period at a black spruce forest in Alaska (64°52' N, 147°51' W, 155 m a.s.l.). We measured ozone concentration gradient by an ozone analyzer (1006-AHJ, Dasibi, USA) continuously at 2 and 8 m above the ground. Half hourly ozone flux was calculated by applying the flux-gradient relationship of sensible heat flux by eddy correlation flux (CSAT3, Campbell Sci., USA) at 6m and the temperature gradient between 2 and 8m by probes (HMP155AC, Väisälä, Finland). Observed ozone concentration was high in daytime under windy condition but low in calm nighttime with a range between 1 and 50 ppbv. Calculated ozone flux (positive and negative values mean upward and downward fluxes, respectively) during the observation period from day of year (DOY) 141and 168 showed mostly positive and ranged up to +20 mg m^-2 day^-1, especially in day time. While that in the latter period from DOY 169 - 196 showed mostly negative ranging up to -20 mg m^-2 day^-1. The observed upward ozone flux was unique and showing the potentiality of ozone production at understory of sub-arctic boreal forest, where permafrost was underlay. Soil thaw depth was 1 mm at the beginning of soil thawing on DOY 135 which deepened to 90 mm on DOY 161 and 270 mm on DOY 204. One of well known ozone precursors is nitrogen oxides, which might be produced in the organic-rich shallow permafrost by soil freezing and thawing process. The new potentiality of ozone production at sub-arctic boreal forest during early thawing period might be an important effect on ecosystem processes such as fertilization. We analyze nitrogen oxides and other ozone precursors during the soil thawing period in our next study. Broad objectives of this work are to gain better understandings of mechanisms and roles of the ozone production at a boreal forest ecosystem of Alaska.