Description: Aerosol particle number concentrations have been measured at Halley and Neumayer on the Antarctic coast, since 2004 and 1984, respectively. Sulphur compounds known to be implicated in particle formation and growth were independently measured: sulphate ions and methane sulphonic acid in filtered aerosol samples and gas phase dimethyl sulphide for limited periods. Iodine oxide, IO, was determined by a satellite sensor from 2003 to 2009 and by different ground-based sensors at Halley in 2004 and 2007. Previous model results and midlatitude observations show that iodine compounds consistent with the large values of IO observed may be responsible for an increase in number concentrations of small particles. Coastal Antarctica is useful for investigating correlations between particles, sulphur, and iodine compounds, because of their large annual cycles and the source of iodine compounds in sea ice. After smoothing all the measured data by several days, the shapes of the annual cycles in particle concentration at Halley and Neumayer are approximated by linear combinations of the shapes of sulphur compounds and IO but not by sulphur compounds alone. However, there is no short-term correlation between IO and particle concentration. The apparent correlation by eye after smoothing but not in the short term suggests that iodine compounds and particles are sourced some distance offshore. This suggests that new particles formed from iodine compounds are viable, i.e., they can last long enough to grow to the larger particles that contribute to cloud condensation nuclei, rather than being simply collected by existing particles. If so, there is significant potential for climate feedback near the sea ice zone via the aerosol indirect effect.

Description: Because investigations of PAN at higher southern latitudes are very scarce, we measuredsurface PAN concentrations for the first time in Antarctica. During the PhotochemicalExperiment at Neumayer (PEAN'99) campaign mean surface PAN mixing ratios of(13 ± 7) pptv and maximum values of 48 pptv were found. When these PAN mixing ratioswere compared to the sum of NOx and inorganic nitrate they were found to be equal orhigher. Low ambient air temperatures and low PAN concentrations caused a slowhomogeneous PAN decomposition rate of approximately 5 x 10^-2 pptv hr^-1. These slowdecay rates were not sufficient to firmly establish the simultaneously observed NOxconcentrations. In addition, low concentration ratios of [HNO3] / [NOx] imply that thephotochemical production of NOx within the snow pack can influence surface NOx mixingratios in Antarctica. Alternate measurements of PAN mixing ratios at two different heightsabove the snow surface were performed to derive fluxes between the lower troposphereand the underlying snow pack using calculated friction velocities. Most of the concentrationdifferences were below the precision of the measurements. Therefore, only an upper limitfor the PAN flux of ± 1 x 10^13 molecules m^-2 s^-1 without a predominant direction canbe estimated. However, PAN fluxes below this limit can still influence both the transfer ofnitrogen compounds between atmosphere and ice, and the PAN budget in higher southernlatitudes.

Description: It has been shown that NOx is produced photochemically within the snowpack of polar regions. If emitted to the atmosphere, this processcould be a major source of NOx in remote snowcovered regions. We report here on measurements made at the German Antarctic station,Neumayer, during austral summer 1999, aimed at detecting and quantifying emissions of NOx from the surface snow. Gradients of NOxwere measured, and fluxes calculated using local meteorology measurements. On the 2 days of flux measurements, the derived fluxesshowed continual release from the snow surface, varying between similar to0 and 3x10(8) molecs/cm(2)/s. When not subject toturbulence, the variation was coincident with the uv diurnal cycle, suggesting rapid release once photochemically produced. Scaling thediurnal average of Feb. 7th (1.3x10(8) molecs/cm(2)/s) suggests an annual emission over Antarctica of the order 0.0076TgN.

Description: The occurence of a diurnal variability in measured total oxidised nitrogen (NOy) was observed at Neumayer, Antarctica, (70°39S, 8°15W) during a recent summer measurement campaign. Minima and maxima occurred in the early morning/early evening respectively, with the amplitude of the cycle around 40% of the daily mean NOy values. Given that this campaign was the first to attempt NOy measurements on the Antarctic continent, it is not presently clear whether this is an Antarctic-wide phenomenon, or local to Neumayer. A similar cycle was observed for HNO3, although HNO3 concentrations and fluctuations are too small to account for all of the NOy variability. In this paper we investigate possible mechanisms that might cause such diurnal signals, focussing on the influence of local meteorology and also of the snow-pack. Exchange processes at the air/snow interface appear to dominate the observed NOy variability, although an influence from the changing surface inversion strength exists. These findings have important implications in understanding and hence correctly interpreting ice core nitrate data.

Description: Abstract. NO, NOy (total reactive nitrogen oxides), gaseous HNO3 and particulate nitrate (p-NO3-) were measured at Neumayer Station from February 1999 to January 2000. We found a mean NOy mixing ratio of 46±29 pptv, with significantly higher values between February and the end of May (58±35 pptv). Between February and November, the (HNO3+p-NO3-)/NOy ratio was extremely low (around 0.22) and in contrast to NOy the seasonality of p-nitrate and HNO3 showed a distinct maximum in November and December, respectively. Trajectory analyses and radioisotope measurements (7Be, 10Be, 210Pb, and 222Rn) indicated that the upper troposphere or stratosphere was the main source region of the observed NOy with a negligible contribution of ground-level sources at northward continents. Frequent maxima of NOy mixing ratios up to 100 pptv are generally associated with air mass transport from the free troposphere of continental Antarctica, while air masses with the lowest NOy mixing ratios were typically advected from the marine boundary layer. Due to the highly variable (HNO3+p-NO3-)/NOy ratio and different seasonality of (HNO3+p-NO3-) and NOy, nitrate concentrations in firn caused by deposition of HNO3 and p-nitrate are most probably not directly connected with the atmospheric budget of reac-tive nitrogen oxides. Consequently, there is no straightforward way to derive the total reactive nitrogen content of the paleo-atmosphere from ice nitrate records.

Description: In controlled experiments carried out at Neumayer, Antarctica, throughout a diurnal cycle,concentrations of NOx (NO + NO2) were measured in air pulled through a snowblock cutfrom the Antarctic surface snow. It was found that the concentrations are higher than thosein ambient air. The production rates of NOx in the snowblock air vary with the intensity ofradiation incident on the block, consistent with photolytic mechanisms. By alternatelyshading and exposing the snowblock to sunlight, it was confirmed that photochemistrydrives the NOx production rates in the snowblock air, with, presumably, nitrate in the snowserving as the reservoir species for the production. These results provide evidence thatphotochemical activity in Antarctic surface snow can significantly increase concentrations ofNO and NO2.

Description: A key focus of the PEAN99 campaign (Photochemical Experimentat Neumayer (70°S, 8°W) January/February 1999) was to studythe photochemistry of reactive nitrogen compounds and theirchemical and physical exchange processes with the firn layer.For the latter, two sets of controlled experiments werecarried out, designed to i) show conclusively that NOxproduction in the snowpack is photochemical, ii) determinewhether NO or NO2 is produced, iii) quantify the productionrate of NO2 and NO inside a snowblock, iv) derive fluxes ofNox from the snow into the overlying atmosphere. Throughouta diurnal cycle, measurements were made of ambient air andof air from inside a snowblock. Enhanced concentrations ofNO and NO2 (up to 15 pptv and 32 pptv, respectively) weremeasured inside the snowblock. The production rate insidethe block varied with intensity of incident radiation, andreached a maximum of 1.1*10(6) molec cm(-3) s(-1) for NO and2.1*10(6) molec cm(-3) s(-1) for NO2. A second experiment,in which the snowblock was alternately exposed to sunlightand then shaded, showed that the diurnal production wasdriven by photochemistry rather than some other diurnallyvarying factor. Gradient measurements and subsequent fluxcalculations showed that the snowpack can be a source of NOxto the overlying atmosphere, but suggest that the sourcestrength varies considerably from day to day.

Description: Surface ozone has been measured since 2004 at the coastal East Antarctic site of Dumont d'Urville (DDU) and since 2007 at the Concordia station located on the high East Antarctic plateau. This paper discusses long-term trends, seasonal and diurnal cycles, as well as inter-annual summer variability observed at these two East Antarctic sites. At Concordia, near surface ozone data were complemented by balloon soundings and compared to similar measurements done at the South Pole. The DDU record is compared to those obtained at the coastal site of Syowa also located in East Antarctica, as well as the coastal sites of Neumayer and Halley, both located at the coast of the Weddell Sea in West Antarctica. Surface ozone mixing ratios exhibit very similar seasonal cycle at Concordia and the South Pole. However, in summer the diurnal cycle and the vertical distribution of ozone above the snow surface are different at the two sites with a drop of ozone in the afternoon at Concordia and not at the South Pole, and a far well-mixed rich ozone layer within the lower 250 m at Concordia than at the South Pole during sunlight hours. These differences are related to different solar radiation and wind regimes encountered at these two inland sites. DDU appears to be the coastal site where the impact of the late winter/spring bromine chemistry is the weakest, but where the impact of NOx snow emissions from the high Antarctic plateau is the highest. The highest impact of the bromine chemistry is seen at Halley and Neumayer, and to a lesser extent at Syowa. These three sites are only weakly impacted by the NOx chemistry and the net ozone production occurring on the high Antarctic plateau. The differences in late winter/spring are attributed to the abundance of sea-ice offshore the sites whereas those in summer are related to the topography of East Antarctica that promotes the katabatic flow bringing oxidant-rich inland air masses to the site. There appears to be a decreasing trend in summer at the two East Antarctic sites of Concordia and DDU over the most recent period (2004/2007–2014). Further researches including continuing monitoring are needed at these two sites to better separate effect of synoptic transport from possible change of NOx snow emissions in response to change of the stratospheric ozone layer.