Abstract
This work focuses on the near-surface O3 variability over the eastern Antarctic Plateau. In particular, eight years (2006–2013) of continuous observations at the WMO/GAW contributing station “Concordia” (Dome C–DMC: 75°06′S, 123°20′E, 3280 m) are presented, in the framework of the Italian Antarctic Research Programme (PNRA). First, the characterization of seasonal and diurnal O3 variability at DMC is provided. Then, for the period of highest data coverage (2008–2013), we investigated the role of specific atmospheric processes in affecting near-surface summer O3 variability, when O3 enhancement events (OEEs) are systematically observed at DMC (average monthly frequency peaking up to 60% in December). As deduced by a statistical selection methodology, these OEEs are affected by a significant interannual variability, both in their average O3 values and in their frequency. To explain part of this variability, we analyzed OEEs as a function of specific atmospheric variables and processes: (i) total column of O3 (TCO) and UV-A irradiance, (ii) long-range transport of air masses over the Antarctic Plateau (by Lagrangian back-trajectory analysis – LAGRANTO), (iii) occurrence of “deep” stratospheric intrusion events (by using the Lagrangian tool STLEFLUX). The overall near-surface O3 variability at DMC is controlled by a day-to-day pattern, which strongly points towards a dominating influence of processes occurring at “synoptic” scales rather than “local” processes. Even if previous studies suggested an inverse relationship between OEEs and TCO, we found a slight tendency for the annual frequency of OEEs to be higher when TCO values are higher over DMC. The annual occurrence of OEEs at DMC seems related to the total time spent by air masses over the Antarctic plateau before their arrival to DMC, suggesting the accumulation of photochemically-produced O3 during the transport, rather than a more efficient local production. Moreover, the identification of recent (i.e., 4-day old) stratospheric intrusion events by STEFLUX suggested only a minor influence (up to 3% of the period, in November) of “deep” events on the variability of near-surface summer O3 at DMC.
Highlights
Tropospheric ozone (O3) is a greenhouse gas and a driver for atmospheric oxidation capacity (Schultz et al, 2015)
The main purpose of this paper is to provide a systematic assessment of the specific processes which affect near-surface summer O3 interannual variability over an East Antarctic plateau area: (i) total column of O3 (TCO) and UV irradiance variability, (ii) synoptic-scale air mass transport within Antarctic interior, and (iii) “deep” stratosphere-to-troposphere transport (STT) transport
This feature appeared to be similar to what recorded at the other permanent continental station in Antarctica, and can be attributed to the occurrence of O3 enhancement events (OEEs) during the period November–January (Oltmans et al, 2008; Helmig et al, 2007)
Summary
Tropospheric ozone (O3) is a greenhouse gas and a driver for atmospheric oxidation capacity (Schultz et al, 2015). Summer episodes of sudden O3 increases were observed within Antarctica interior (e.g., Crawford et al, 2001; Legrand et al, 2009), and at coastal sites affected by air mass transport from the interior of the continent (e.g., Cristofanelli et al, 2011) These events were attributed to the photo-denitrification of the summer snowpack, resulting in NOX emissions to the atmosphere and subsequent photochemical O3 production (Jones et al, 1999, 2000). The direct transport of air masses enriched in O3 would represent another process by which stratosphere-to-troposphere transport (STT) events can potentially affect O3 in the Antarctic troposphere
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