http://journals.cambridge.org Downloaded: 11 Dec 2013 IP address: 186.167.64.99 Analysis of near-surface ozone variations in Terra Nova Bay, Antarctica P. CRISTOFANELLI, P. BONASONI*, F. CALZOLARI, U. BONAFE ` , C. LANCONELLI, A. LUPI, G. TRIVELLONE, V. VITALE and B. PETKOV ISAC-CNR, Via Gobetti 101, 40129 Bologna, Italy *Corresponding author: P.Bonasoni@isac.cnr.it Abstract: Ozone concentration measurements were made during December from 2001–2005 to quantify the contributions of different processes to near-surface ozone concentrations (O 3 ) in Terra Nova Bay, Antarctica. The average O 3 concentration was 20.3 ppbv. On days characterized by high solar radiation fluxes (HSR), significantly higher concentrations of O 3 (21.3 ppbv) were recorded compared to days with low solar radiation fluxes (LSR days, 16.8 ppbv). High O 3 concentrations could be related to strong winds from SW–NW. Three-dimensional back-trajectories show that air from the interior of the continent could affect O 3 at Terra Nova Bay. Moreover, during HSR days, high O 3 concentrations were also recorded in connection with weak circulation, suggesting that emissions from the Italian base (located 2 km north) could also represent a significant source of O 3 . To clarify the role of local pollution in Terra Nova Bay, O 3 values were also calculated using the photochemical steady state (PSS) approximation under clear sky and cloudy conditions. Received 11 April 2007, accepted 2 October 2007 Key words: katabatic wind, solar radiation fluxes, surface ozone, tropospheric ozone Introduction In the troposphere, ozone (O 3 ) is one of the most active gases involved in photochemical reactions. In fact, being the precursor of important oxidizing radicals (i.e. OH and NO 3 ), O 3 is one of the key agents influencing the oxidizing capacity of the troposphere. In Antarctica, several processes can influence tropospheric O 3 concentrations, e.g. photochemical processes involving reactive halogen atoms (Barrie et al. 1988, Roscoe et al. 2001, Tarasick & Bottenheim 2002) and NO x (Crawford et al. 2001) as well as transport of air masses from lower latitudes (Murayama et al. 1992, Gruzdev & Stinov 1992) or vertical transport (Grudzev et al. 1993). During the summer season, the photochemical production of NO x (Jones et al. 2001, Davis et al. 2001, Beine et al. 2002) due to the photolysis of NO 3- in snowpack interstitial air, as well as the photolysis of atmospheric HONO (Yang et al. 2002), can occur in the Polar Regions thus providing a surprisingly active photochemical environment. Accurate knowledge of the latitudinal distribution of O 3 is needed to improve global modelling of O 3 and future levels of atmospheric greenhouse gases. That is why, within the framework of the Italian National Programme of Antarctic Researches (PNRA), continuous measurements of summer surface O 3 concentrations have been carried out at the Italian Antarctic research station at Terra Nova Bay (TNB) (Mario Zucchelli Station - 74.78S, 164.18E, 41 m a.s.l.) since 2001. In this paper, these near-surface ozone measurements will be presented and analysed for the first time. Measurement site and method The TNB M. Zucchelli summer station is located on the western edge of the Ross Sea (Fig. 1). During the period 2001–2005, five summer campaigns for the determination of surface O 3 concentrations were conducted at the clean- air facility of Icaro Camp (TNB-IC) located on the coast 2 km south from the main station. The O 3 measurements were undertaken in a purpose designed shelter with an air intake 5 m above the surface composed of a 2 m long Pyrex stack (67 mm diameter) enclosed in a steel cover. Air is forced through this by a blower with a flux velocity ranging from 1–3 m s -1 . Ozone measurements (at 1.8 l min -1 ) were made every minute and with a precision and accuracy of  1 ppbv. Zero and span checks were automatically performed every 24 hours. Moreover, after each experimental campaign the O 3 analyser (DASIBI 1108 PC) was returned to the factory for ordinary maintenance and calibration. Standard meteorological parameters were continuously observed at 1 min intervals using an IRDAM WST7000 meteorological station at a height of 6 m above the ground. Surface measurements of shortwave incoming solar radiation (SW in ) were obtained using a CNR-1 Kipp & Zonen radiometer with a sensitivity of 10–35 lV Wm -2 in the spectral range from 305–2800 nm. At TNB-IC, the seasonal behaviour of SW in is characterized by a seasonal cycle with a relatively flat maximum in December (not shown here). Because of this characteristic pattern O 3 and meteorological parameters (on hourly basis) as well as SW in (daily average values) have 415 Antarctic Science 20 (4), 415–421 (2008) & Antarctic Science Ltd 2008 Printed in the UK doi:10.1017/S0954102008001028