Formaldehyde (HCHO) in air, snow and interstitial air at Concordia (East Antarctic plateau) in summer

During the 2011/12 and 2012/13 austral summers, HCHO was investigated for the first time in ambient air, snow, and interstitial air at the Concordia site, located near Dome C on the East Antarctic Plateau, by deploying an Aerolaser AL-4021 analyzer. Snow emission fluxes were estimated from vertical gradients of mixing ratios observed at 1 cm and 1 m above the snow surface as well as in interstitial air a few centimeters below the surface and in air just above the snowpack. Typical flux values range between 1 and 2 × 1012 molecules m−2 s−1 at night and 3 and 5 × 1012 molecules m−2 s−1 at noon. Shading experiments suggest that the photochemical HCHO production in the snowpack at Concordia remains negligible compared to temperature-driven air–snow exchanges. At 1 m above the snow surface, the observed mean mixing ratio of 130 pptv and its diurnal cycle characterized by a slight decrease around noon are quite well reproduced by 1-D simulations that include snow emissions and gas-phase methane oxidation chemistry. Simulations indicate that the gas-phase production from CH4 oxidation largely contributes (66%) to the observed HCHO mixing ratios. In addition, HCHO snow emissions account for ~ 30% at night and ~ 10% at noon to the observed HCHO levels

Air–snow transfer of nitrate on the East Antarctic Plateau - Part 1: Isotopic evidence for a photolytically driven dynamic equilibrium in summer

Here we report the measurement of the comprehensive isotopic composition (δ15N, Δ17O and δ18O) of nitrate at the air–snow interface at Dome C, Antarctica (DC, 75°06' S, 123°19' E), and in snow pits along a transect across the East Antarctic Ice Sheet (EAIS) between 66° S and 78° S. In most of the snow pits, nitrate loss (either by physical release or UV photolysis of nitrate) is observed and fractionation constants associated are calculated. Nitrate collected from snow pits on the plateau (snow accumulation rate below 50 kg m−2 a−1) displays average fractionation constants of (−59±10) ‰, (+2.0±1.0) ‰ and (+8.7±2.4)‰ for δ15N, Δ17O and δ18O, respectively. In contrast, snow pits sampled on the coast show distinct isotopic signatures with average fractionation constants of (−16±14) ‰, (−0.2±1.5) ‰ and (+3.1±5.8) ‰, for δ15N, Δ17O and δ18O, respectively. Our observations corroborate that photolysis (associated with a 15N / 14N fractionation constant of the order of –48 ‰ according to Frey et al. (2009) is the dominant nitrate loss process on the East Antarctic Plateau, while on the coast the loss is less pronounced and could involve both physical release and photochemical processes. Year-round isotopic measurements at DC show a~close relationship between the Δ17O of atmospheric nitrate and Δ17O of nitrate in skin layer snow, suggesting a photolytically driven isotopic equilibrium imposed by nitrate recycling at this interface. Atmospheric nitrate deposition may lead to fractionation of the nitrogen isotopes and explain the almost constant shift of the order of 25 ‰ between the δ15N values in the atmospheric and skin layer nitrate at DC. Asymptotic δ15N(NO3−) values calculated for each snow pit are found to be correlated with the inverse of the snow accumulation rate (ln(δ15N as. + 1) = (5.76±0.47) ċ (kg m−2 a−1/ A) + (0.01±0.02)), confirming the strong relationship between the snow accumulation rate and the degree of isotopic fractionation, consistent with previous observations by Freyer et al. (1996). Asymptotic Δ17O(NO3−) values on the plateau are smaller than the values found in the skin layer most likely due to oxygen isotope exchange between the nitrate photoproducts and water molecules from the surrounding ice. However, the apparent fractionation in Δ17O is small, thus allowing the preservation of a portion of the atmospheric signal

Oxygen isotope mass balance of atmospheric nitrate at Dome C, East Antarctica, during the OPALE campaign

Variations in the stable oxygen isotope composition of atmospheric nitrate act as novel tools for studying oxidative processes taking place in the troposphere. They provide both qualitative and quantitative constraints on the pathways determining the fate of atmospheric nitrogen oxides (NO + NO₂ = NO_<i>x</i>). The unique and distinctive ¹⁷O excess (Δ¹⁷O = <i>δ</i>¹⁷O − 0.52 × <i>δ</i>¹⁸O) of ozone, which is transferred to NO_<i>x</i> via oxidation, is a particularly useful isotopic fingerprint in studies of NO_<i>x</i> transformations. Constraining the propagation of ¹⁷O excess within the NO_<i>x</i> cycle is critical in polar areas, where there exists the possibility of extending atmospheric investigations to the glacial–interglacial timescale using deep ice core records of nitrate. Here we present measurements of the comprehensive isotopic composition of atmospheric nitrate collected at Dome C (East Antarctic Plateau) during the austral summer of 2011/2012. Nitrate isotope analysis has been here combined for the first time with key precursors involved in nitrate production (NO_<i>x</i>, O₃, OH, HO₂, RO₂, etc.) and direct observations of the transferrable Δ¹⁷O of surface ozone, which was measured at Dome C throughout 2012 using our recently developed analytical approach. Assuming that nitrate is mainly produced in Antarctica in summer through the OH + NO₂ pathway and using concurrent measurements of OH and NO₂, we calculated a Δ¹⁷O signature for nitrate on the order of (21–22 ± 3) ‰. These values are lower than the measured values that ranged between 27 and 31 ‰. This discrepancy between expected and observed Δ¹⁷O(NO₃⁻) values suggests the existence of an unknown process that contributes significantly to the atmospheric nitrate budget over this East Antarctic region. However, systematic errors or false isotopic balance transfer functions are not totally excluded

Spatial and diurnal variability in reactive nitrogen oxide chemistry as reflected in the isotopic composition of atmospheric nitrate: Results from the CalNex 2010 field study

International audiencewe present measurements of the size-resolved concentration and isotopic composition of atmospheric nitrate (NO3-) collected during a cruise in coastal California. Significant differences in air mass origin and atmospheric chemistry were observed in the two main regions of this cruise (South and Central Coast) with corresponding differences in NO3- concentration and isotope ratios. Measurements of the 17O-excess (Δ17O) of NO3- suggest that nocturnal chemistry played an important role in terms of total NO3- production ( 50%) in the coastal Los Angeles region (South Coast), where NO3- concentrations were elevated due to the influence of sea breeze / land breeze recirculation and Δ17O(NO3-) averaged (25.3 ± 1.6)‰. Conversely, Δ17O(NO3-) averaged (22.3 ± 1.8)‰ in the Central Coast region, suggesting that the daytime OH + NO2 reaction was responsible for 60-85% of NO3- production in the marine air sampled in this area. A strong diurnal signal was observed for both the Δ17O and δ15N of NO3-. In the case of Δ17O, this trend is interpreted quantitatively in terms of the relative proportions of daytime and nighttime production and the atmospheric lifetime of NO3-. For δ15N, which had an average value of (0.0 ± 3.2)‰, the observed diurnality suggests a combined effect of isotopic exchange between gas-phase precursors and variability in reactive nitrogen sources. These findings represent a significant advance in our understanding of the isotope dynamics of nitrate and its precursor molecules, with potentially important implications for air quality modeling

'Making friends with the neighbours': blogging as a research method

During my research about women and surfing, I have found writing a blog useful as a tool for doing research in the cultural context of surfing. More than a simply a space to increase transparency in my ethnographic research process, blogging became a method of its own. Linking Elizabeth St Pierre's discussion of research 'folds' with Elspeth Probyn's encouragement to 'think the social through myself', blogging helped to address feminist concerns that research remains relevant to lived cultural understandings and experiences of the women participating. Blogging also helped in developing a language and a style of writing that reflects the experiences of surfing in a culturally meaningful way, and to provide a way of locating my own subjectivity within the research space. Through blogging I have been able to keep fieldnotes and ideas alive, engaged and in exchange throughout the project, moving and shifting through both theory and culture