Seasonal cycles of nonmethane hydrocarbons and methyl chloride, as derived from firn air from Dronning Maud Land, Antarctica (original) (raw)
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Atmospheric Environment, 2010
Multiyear (2000e2006) seasonal measurements of carbon monoxide, hydrocarbons, halogenated species, dimethyl sulfide, carbonyl sulfide and C 1 eC 4 alkyl nitrates at the South Pole are presented for the first time. At the South Pole, short-lived species (such as the alkenes) typically were not observed above their limits of detection because of long transit times from source regions. Peak mixing ratios of the longer lived species with anthropogenic sources were measured in late winter (August and September) with decreasing mixing ratios throughout the spring. In comparison, compounds with a strong oceanic source, such as bromoform and methyl iodide, had peak mixing ratios earlier in the winter (June and July) because of decreased oceanic production during the winter months. Dimethyl sulfide (DMS), which is also oceanically emitted but has a short lifetime, was rarely measured above 5 pptv. This is in contrast to high DMS mixing ratios at coastal locations and shows the importance of photochemical removal during transport to the pole. Alkyl nitrate mixing ratios peaked during April and then decreased throughout the winter. The dominant source of the alkyl nitrates in the region is believed to be oceanic emissions rather than photochemical production due to low alkane levels.
Journal of Geophysical Research: Atmospheres, 2001
The atmospheric trend of methane isotopic ratios since the mid‐20th century has been reconstructed from Antarctic firn air. High volume air samples were extracted at several depth levels at two sites in East Antarctica. Methane concentration and its 13C/12C and D/H ratios were determined by gas chromatography, mass spectrometry, and infrared spectroscopy. A firn air transport model was applied to reconstruct past atmospheric trends in methane and its isotopic composition. By subsequent application of an atmospheric model, changes in methane sources and OH sink compatible with the past atmospheric trends are explored. In step with increasing methane mixing ratios, δ13C increased by ∼1.7‰ over the last 50 years. These changes mainly reflect a shift in relative source strength toward the heavier anthropogenic methane source, such as biomass burning and methane of nonbiological origin. The δD (CH4) showed a period of decline between the 1950s and 1975, followed by a gradual increase of ...
Tellus B, 2007
as part of the Chemistry of the Antarctic Boundary Layer and the Interface with Snow (CHABLIS) experiment. The data show long-and short-term variabilities in NMHCs controlled by the seasonal and geographic dependence of emissions and variation in atmospheric removal rates and pathways. Ethane, propane, iso-butane, n-butane and acetylene abundances followed a general OH-dependent sinusoidal seasonal cycle. The yearly averages were 186, 31, 3.2, 4.9 and 19 pptV, respectively, lower than those which were reported in some previous studies. Superimposed on a seasonal cycle was shorter-term variability that could be attributed to both synoptic airmass variability and localized loss processes due to other radical species. Hydrocarbon variability during periods of hour-to-day-long surface O 3 depletion in late winter/early spring indicated active halogen atom chemistry estimated to be in the range 1.7 × 10 3 -3.4 × 10 4 atom cm −3 for Cl and 4.8 × 10 6 -9.6 × 10 7 atom cm −3 for Br. Longer-term negative deviations from sinusoidal behaviour in the late August were indicative of NMHC reaction with a persistent [Cl] of 2.3 × 10 3 atom cm −3 . Maximum ethene and propene of 157 and 179 pptV, respectively, were observed in the late February/early March, consistent with increased oceanic biogenic emissions; however, their presence was significant year-round (June-August concentrations of 17.1 ± 18.3 and 7.9 ± 20.0 pptV, respectively).
Atmospheric Chemistry and Physics Discussions, 2005
Although for several atmospheric trace gases trends over the past 100 year have been reconstructed using firn air analyses, little is known about one of the chemically most significant trace gases, namely CO. Among the 3 Antarctic drilling expeditions reported, the one from Berkner Island appears to have given results of sufficient analytical quality to warrant a modelling with the aim to reconstruct past changes in atmospheric CO. Based on our reconstructions, CO in high latitudes of the Southern Hemisphere has been increasing since beginning of the 20th century from ∼38 ppbv to a recent value of about 52.5 ppbv. The increase in CO is mainly explained by the known increase in CH 4 , with biomass burning output being most likely responsible for an additional increase. Which, if any, role changes in OH have played cannot be derived.
Atmospheric Chemistry and Physics, 2007
Trends of carbon monoxide (CO) for the past 100 years are reported as derived from Antarctic firn drilling expeditions. Only one of 3 campaigns provided high quality results. The trend was reconstructed using a firn air model in the forward mode to constrain age distributions and assuming the CO increase to be proportional to its major source, namely CH 4. The results suggest that CO has increased by ∼38%, from 38±7 to 52.5±1.5 ppbv over a period of roughly 100 years. The concentrations are on the volumetric scale which corresponds to ∼1.08 of the scale used by NOAA/CMDL. The estimated CO increase is somewhat larger than what is estimated from the CO budget estimations and the CH 4 growth alone. The most likely explanation might be an increase in biomass burning emissions. Using CH 3 Cl as another proxy produces a very similar reconstruction.
Model calculations of the age of firn air across the Antarctic continent
Atmospheric Chemistry and Physics, 2004
The age of firn air in Antarctica at pore close-off depth is only known for a few specific sites where firn air has been sampled for analyses. We present a model that calculates the age of firn air at pore close-off depth for the entire Antarctic continent. The model basically uses four meteorological parameters as input (surface temperature, pressure, 5 accumulation rate and wind speed). Using parameterisations for surface snow density, pore close-off density and tortuosity, in combination with a density-depth model and data of a regional atmospheric climate model, distribution of pore close-off depth for the entire Antarctic continent is determined. The deepest pore close-off depth was found for the East Antarctic Plateau near 72 • E, 82 • S, at 150±15 m (2σ). A firn air 10 diffusion model was applied to calculate the age of CO 2 at pore close-off depth. The results predict that the oldest firn gas (CO 2 age) is located between Dome Fuji, Dome Argos and Vostok at 43
Journal of Geophysical Research, 2003
1] We report measurements of light (C 2 -C 4 ) nonmethane hydrocarbons (NMHCs) and C 1 -C 4 alkyl nitrates made at Summit, Greenland, over a full annual cycle (June 1997(June -1998. The remoteness of the Summit camp from industrial source regions resulted in trends of these trace gases that showed a clear seasonal variation with low variability. Variability (calculated as the percentage 1-sigma deviation of a running 10-point mean) averaged 7-9% for ethane over the entire study. The shorter-lived species (ethyne, propane, and the butanes) exhibited variability from 12-20% in winter to 20-100% in summer. The best fit curve to the annual cycle of ethane is a sinusoidal oscillation, but each of the shorter-lived NMHCs exhibited flat periods of low concentrations during the summer months. The C 2 -C 4 NMHCs peaked between 8 and 24 February, with the longer-lived NMHCs maximizing latest. These data were broadly consistent with literature values, confirming that high-latitude Northern Hemisphere (NH) emissions are similar year to year. Employing their linear fall accumulation rates, we calculated average NMHC ratios versus ethane of 0.59(±0.10):0.33(±0.05):0.26(±0.08):0.14(±0.04) for propane, ethyne, n-butane, and ibutane, respectively. We suggest that these ratios represent useful quantities with which to compare averaged mid-and high-latitude NH emission ratios. We also report the first yearround observations of the seasonal cycle of light C 1 -C 4 alkyl nitrates. Similar to the NMHCs, the seasonal trend of these gases shows primary dependence on transport to Summit during winter, and photochemical removal during summer. Unlike their parent NMHCs, alkyl nitrate concentrations did not asymptote to low levels during summer and they exhibited winter maxima later with decreasing photochemical lifetime.