Search

Carbonyl sulfide (COS) and other trace gases were measured in firn air collected near South Pole (89.98°S) and from air trapped in ice at Siple Dome, Antarctica (81.65°S). The results, when considered with ambient air data and previous ice core measurements, provide further evidence that atmospheric mixing ratios of COS over Antarctica between 1650 and 1850 A.D. were substantially lower than those observed today. Specifically, the results suggest annual mean COS mixing ratios between 300 and 400 pmol mol−1 (ppt) during 1650–1850 A.D. and increases throughout most of the twentieth century. Measurements of COS in modern air and in the upper layers of the firn at South Pole indicate ambient, annual mean mixing ratios between 480 and 490 ppt with substantial seasonal variations. Peak mixing ratios are observed during austral summer in ambient air at South Pole and Cape Grim, Tasmania (40.41°S). Provided COS is not produced or destroyed in firn, these results also suggest that atmospheric COS mixing ratios have decreased 60–90 ppt (10–16%) since the 1980s in high latitudes of the Southern Hemisphere. The history derived for atmospheric mixing ratios of COS in the Southern Hemisphere since 1850 is closely related to historical anthropogenic sulfur emissions. The fraction of anthropogenic sulfur emissions released as COS (directly or indirectly) needed to explain the secular changes in atmospheric COS over this period is 0.3–0.6%.

We present a comprehensive estimate of nitrous oxide (N2O) emissions using observations and models from 1995 to 2008. High-frequency records of tropospheric N2O are available from measurements at Cape Grim, Tasmania; Cape Matatula, American Samoa; Ragged Point, Barbados; Mace Head, Ireland; and at Trinidad Head, California using the Advanced Global Atmospheric Gases Experiment (AGAGE) instrumentation and calibrations. The Global Monitoring Division of the National Oceanic and Atmospheric Administration/Earth System Research Laboratory (NOAA/ESRL) has also collected discrete air samples in flasks and in situ measurements from remote sites across the globe and analyzed them for a suite of species including N2O. In addition to these major networks, we include in situ and aircraft measurements from the National Institute of Environmental Studies (NIES) and flask measurements from the Tohoku University and Commonwealth Scientific and Industrial Research Organization (CSIRO) networks. All measurements show increasing atmospheric mole fractions of N2O, with a varying growth rate of 0.1-0.7% per year, resulting in a 7.4% increase in the background atmospheric mole fraction between 1979 and 2011. Using existing emission inventories as well as bottom-up process modeling results, we first create globally gridded a priori N2O emissions over the 37 years since 1975. We then use the threedimensional chemical transport model, Model for Ozone and Related Chemical Tracers version 4 (MOZART v4), and a Bayesian inverse method to estimate global as well as regional annual emissions for five source sectors from 13 regions in the world. This is the first time that all of these measurements from multiple networks have been combined to determine emissions. Our inversion indicates that global and regional N2O emissions have an increasing trend between 1995 and 2008. Despite large uncertainties, a significant increase is seen from the Asian agricultural sector in recent years, most likely due to an increase in the use of nitrogenous fertilizers, as has been suggested by previous studies. [ABSTRACT FROM AUTHOR]

Vertical profiles of CFC-11 (CCl3F) and CFC-12 (CCl2F2) have been measured with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) with global coverage under daytime and nighttime conditions. The profile retrieval is based on constrained nonlinear least squares fitting of measured limb spectral radiance to modeled spectra. CFC-11 is measured in its v4-band at 850 cm-1, and CFC-12 is analyzed in its v6-band at 922 cm-1. To stabilize the retrievals, a Tikhonov-type smoothing constraint is applied. Main retrieval error sources are measurement noise and elevation pointing uncertainties. The estimated CFC-11 retrieval errors including noise and parameter errors but excluding spectroscopic data uncertainties are below 10 pptv in the middle stratosphere, depending on altitude, the MI-PAS measurement mode and the actual atmospheric situation. For CFC-12 the total retrieval errors are below 28 pptv at an altitude resolution varying from 3 to 5 km. Time series of altitude/latitude bins were fitted by a simple parametric approach including constant and linear terms, a quasi-biennial oscillation (QBO) proxy and sine and cosine terms of several periods. In the time series from 2002 to 2011, quasi-biennial and annual oscillations are clearly visible. A decrease of stratospheric CFC mixing ratios in response to the Montreal Protocol is observed for most altitudes and latitudes. However, the trends differ from the trends measured in the troposphere, they are even positive at some latitudes and altitudes, and can in some cases only be explained by decadal changes in atmospheric age of air spectra or vertical mixing patterns. [ABSTRACT FROM AUTHOR]

The article presents a study which aims to improve measurement precision of sulfur hexafluoride (SF6) through the use of a modified Porapak-Q method. The study modified a common gas chromatography-electron capture detector (GC-ECD) method and used global mean SF6 measurements to examine changes in the growth rate and emissions. Results show the consistency of the methods as the SF6 precision was improved from 1-2% to better 25 than 0.5 %.