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2014
Thompson, RL, Chevallier F, Crotwell AM, Dutton G, Langenfelds RL, Prinn RG, Weiss RF, Tohjima Y, Nakazawa T, Krummel PB, Steele LP, Fraser P, O'Doherty S, Ishijima K, Aoki S.  2014.  Nitrous oxide emissions 1999 to 2009 from a global atmospheric inversion. Atmospheric Chemistry and Physics. 14:1801-1817.   10.5194/acp-14-1801-2014   AbstractWebsite

N2O surface fluxes were estimated for 1999 to 2009 using a time-dependent Bayesian inversion technique. Observations were drawn from 5 different networks, incorporating 59 surface sites and a number of ship-based measurement series. To avoid biases in the inverted fluxes, the data were adjusted to a common scale and scale offsets were included in the optimization problem. The fluxes were calculated at the same resolution as the transport model (3.75 degrees longitude x 2.5 degrees latitude) and at monthly time resolution. Over the 11-year period, the global total N2O source varied from 17.5 to 20.1 Tg a(-1) N. Tropical and subtropical land regions were found to consistently have the highest N2O emissions, in particular in South Asia (20 +/- 3% of global total), South America (13 +/- 4 %) and Africa (19 +/- 3 %), while emissions from temperate regions were smaller: Europe (6 +/- 1 %) and North America (7 +/- 2 %). A significant multi-annual trend in N2O emissions (0.045 Tg a(-2) N) from South Asia was found and confirms inventory estimates of this trend. Considerable interannual variability in the global N2O source was observed (0.8 Tg a(-1) N, 1 standard deviation, SD) and was largely driven by variability in tropical and subtropical soil fluxes, in particular in South America (0.3 Tg a(-1) N, 1 SD) and Africa (0.3 Tg a(-1) N, 1 SD). Notable variability was also found for N2O fluxes in the tropical and southern oceans (0.15 and 0.2 Tg a(-1) N, 1 SD, respectively). Interannual variability in the N2O source shows some correlation with the El Nino-Southern Oscillation (ENSO), where El Nino conditions are associated with lower N2O fluxes from soils and from the ocean and vice versa for La Nina conditions.

2013
Thompson, RL, Dlugokencky E, Chevallier F, Ciais P, Dutton G, Elkins JW, Langenfelds RL, Prinn RG, Weiss RF, Tohjima Y, O'Doherty S, Krummel PB, Fraser P, Steele LP.  2013.  Interannual variability in tropospheric nitrous oxide. Geophysical Research Letters. 40:4426-4431.   10.1002/grl.50721   AbstractWebsite

Observations of tropospheric N2O mixing ratio show significant variability on interannual timescales (0.2ppb, 1 standard deviation). We found that interannual variability in N2O is weakly correlated with that in CFC-12 and SF6 for the northern extratropics and more strongly correlated for the southern extratropics, suggesting that interannual variability in all these species is influenced by large-scale atmospheric circulation changes and, for SF6 in particular, interhemispheric transport. N2O interannual variability was not, however, correlated with polar lower stratospheric temperature, which is used as a proxy for stratosphere-to-troposphere transport in the extratropics. This suggests that stratosphere-to-troposphere transport is not a dominant factor in year-to-year variations in N2O growth rate. Instead, we found strong correlations of N2O interannual variability with the Multivariate ENSO Index. The climate variables, precipitation, soil moisture, and temperature were also found to be significantly correlated with N2O interannual variability, suggesting that climate-driven changes in soil N2O flux may be important for variations in N2O growth rate.

2001
Rhew, RC, Miller BR, Vollmer MK, Weiss RF.  2001.  Shrubland fluxes of methyl bromide and methyl chloride. Journal of Geophysical Research-Atmospheres. 106:20875-20882.   10.1029/2001jd000413   AbstractWebsite

Flux measurements in coastal sage scrub, chamise chaparral, and creosote bush scrub environments show that methyl bromide (CH(3)Br) and methyl chloride (CH(3)Cl), compounds that are involved in stratospheric ozone depletion, are both produced and consumed by southern California shrubland ecosystems. CH(3)Br and CH(3)Cl are produced in association with a variety of plants and are consumed by the soils, although there is a large variability in the fluxes, depending on predominant vegetation and environmental conditions. At sites with a net uptake of both compounds the fluxes of CH(3)Cl and CH(3)Br show a strong correlation, with a molar ratio of roughly 40:1, pointing to a similar mechanism of consumption. In contrast, the net production rates of these compounds show no apparent correlation with each other. The average observed net CH(3)Br uptake rates are an order of magnitude smaller than the previously reported average soil consumption rates assigned to shrublands. Extrapolations from our field measurements suggest that shrublands globally have a maximum net consumption of <1 Gg yr(-1) for CH(3)Br and < 20 Gg yr(-1) for CH(3)Cl and may, in fact, be net sources for these compounds. Consequently, the measured net fluxes from shrubland ecosystems can account for part of the present imbalance in the CH(3)Br budget by adding a new source term and potentially reducing the soil sink term. These results also suggest that while shrubland soil consumption of CH(3)Cl may be small, soils in general may be a globally significant sink for CH(3)Cl.