Observation of widespread depletion of ozone in the springtime boundary layer of the central Arctic linked to mesoscale synoptic conditions

International audienceRecurrent and episodic depletions of ozone (O3) in the atmospheric boundary layer have been observed at arctic coastal sites during springtime for the past 25 years. Additional measurements from the central Arctic Ocean in April 2003 and 2007 confirm previous observations in 1994 indicating that low (<5 nmol mol‑1) O3 levels most likely represent the normal state of the boundary layer of the Arctic Ocean in springtime. Ozone mixing ratios increase sporadically to typical remote background values only during the approach of lows moving northward into the central Arctic from midlatitudes, bringing O3-rich air into the Arctic basin. During a vast majority of the observed O3 transitions related to the influence of lows, O3 mixing ratios are strongly negatively correlated to atmospheric pressure. This negative correlation is generally stronger than the correlation between O3 mixing ratios and air temperature. The observations indicate that the stable boundary layer, which is a large-scale feature of the Arctic Ocean in springtime, may regularly be void of O3 implying a shift to halogen radicals as the major oxidizing agent on the same spatial scale. The removal of O3 in the boundary layer on such a large scale may contribute to a reduction of the warming caused by tropospheric O3 in the Arctic, although the overall impact on the radiation budget is currently unknown

Regular Airborne Surveys of Arctic Sea Ice and Atmosphere

Accurate fine-scale measurements of sea ice thicknesses and of the Arctic troposphere cannot easily be obtained or validated by satellites alone. To get these key data, necessary for better understanding the rapidly changing Arctic, a new project began conducting airborne surveys in 2009; efforts are under way to make the surveys an annual occurrence

Alkenes in the Arctic boundary layer at Alert, Nunavut, Canada

Measurements of ethene and other non-methane hydrocarbons are reported from intensive measurements campaigns in spring 1998 and 2000. It is argued that the observed levels and the scatter in the data records that have been seen before, are real and not due to canister or other sampling related artifacts. It is then shown that these observations imply that there are local sources for alkenes in the Arctic. Gradient and flux measurements are reported that suggest that this source is in the snow-pack. The flux of ethene out of the snow-pack is estimated to be of the order of 1×10 7 molecules cm −2 s 1 and may be photochemically induced. While small, it is shown that this rate could explain a significant fraction of the observed ethene levels during a typical O 3 depletion episode at Alert

Tracing the Origin and Fate of NOx in the Arctic Atmosphere Using Stable Isotopes in Nitrate

International audienceAtmospheric nitrogen oxides (NOx =NO+ NO2) play a pivotal role in the cycling of reactive nitrogen (ultimately deposited as nitrate) and the oxidative capacity of the atmosphere. Combined measurements of nitrogen and oxygen stable isotope ratios of nitrate collected in the Arctic atmosphere were used to infer the origin and fate of NOx and nitrate on a seasonal basis. In spring, photochemically driven emissions of reactive nitrogen from the snowpack into the atmosphere make local oxidation of NOx by bromine oxide the major contributor to the nitrate budget. The comprehensive isotopic composition of nitrate provides strong constraints on the relative importance of the key atmospheric oxidants in the present atmosphere, with the potential for extension into the past using ice cores

Snowpack photochemical production of HONO: A major source of OH in the Arctic boundary layer in springtime

Both snow manipulation experiments and ambient measurements during the Polar Sunrise Experiment 2000 at Alert (Alert2000) indicate intensive photochemical production of nitrous acid (HONO) in the snowpack. This process constitutes a major HONO source for the overlying atmospheric boundary layer in the Arctic during the springtime, and sustained concentrations of HONO high enough that upon photolysis they became the dominant hydroxyl radical (OH) source. This implies a much greater role for OH radicals in Arctic polar sunrise chemistry than previously believed. Although the observations were made in the high Arctic, this finding has a significant implication for the boundary layer atmospheric chemistry in Antarctica during sunlit seasons and in the mid to high latitudes of the Northern Hemisphere during the winter and spring seasons when approximately 50% of the land mass may be covered by snow