A study determined the atmospheric concentrations and lifetime of trichloroethane (CH3CCl3) and global hydroxyl radical (OH) concentrations. The deduced HO concentration showed little change from ...1978 to 1994.
High‐frequency, in situ observations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and System for Observation of halogenated Greenhouse gases in Europe (SOGE) networks for the period ...1998 to 2008, combined with archive flask measurements dating back to 1978, have been used to capture the rapid growth of HFC‐125 (CHF2CF3) in the atmosphere. HFC‐125 is the fifth most abundant HFC, and it currently makes the third largest contribution of the HFCs to atmospheric radiative forcing. At the beginning of 2008 the global average was 5.6 ppt in the lower troposphere and the growth rate was 16% yr−1. The extensive observations have been combined with a range of modeling techniques to derive global emission estimates in a top‐down approach. It is estimated that 21 kt were emitted globally in 2007, and the emissions are estimated to have increased 15% yr−1 since 2000. These estimates agree within approximately 20% with values reported to the United Nations Framework Convention on Climate Change (UNFCCC) provided that estimated emissions from East Asia are included. Observations of regionally polluted air masses at individual AGAGE sites have been used to produce emission estimates for Europe (the EU‐15 countries), the United States, and Australia. Comparisons between these top‐down estimates and bottom‐up estimates based on reports by individual countries to the UNFCCC show a range of approximately four in the differences. This process of independent verification of emissions, and an understanding of the differences, is vital for assessing the effectiveness of international treaties, such as the Kyoto Protocol.
Tropospheric ozone columns derived from differences between the Dutch‐Finnish Aura Ozone Monitoring Instrument (OMI) measurements of the total atmospheric ozone column and the Aura Microwave Limb ...Sounder (MLS) measurements of stratospheric ozone columns are discussed. Because the measurements by these two instruments are not spatially coincident, interpolation techniques, with emphasis on mapping the stratospheric columns in space and time using the relationships between lower stratospheric ozone and potential vorticities (PV) and geopotential heights (Z), are evaluated. It is shown that this PV mapping procedure produces somewhat better agreement in comparisons with ozonesonde measurements, particularly in winter, than does simple linear interpolation of the MLS stratospheric columns or the use of typical coincidence criteria. The OMI/MLS derived tropospheric columns are calculated to be 4 Dobson units (DU) smaller than the sonde measured columns. This mean difference is consistent with the MLS (version 1.5) stratospheric ozone columns being high relative to Stratospheric Aerosol and Gas Experiment (SAGE II) columns by 3 DU. Standard deviations between the derived tropospheric columns and those measured by ozonesondes are 9 DU (30%) annually but they are just 6 DU (15%) in summer. Uncertainties in the interpolated MLS stratospheric columns are likely to be the primary cause of these standard deviations. An important advantage of the PV mapping approach is that it works well when MLS data are missing (e.g., when an orbit of measurements is missing). In the comparisons against ozonesonde measurements, it provides up to twice as many comparisons compared to the other techniques.
Continuous measurements of methane since 1986 at the Global Atmospherics Gases Experiment/Advanced Global Atmospherics Gases Experiment (GAGE/AGAGE) surface sites are described. The precisions range ...from approximately 10 ppb at Mace Head, Ireland, during GAGE to better than 2 ppb at Cape Grim, Tasmania, during AGAGE (i.e., since 1993). The measurements exhibit good agreement with coincident measurements of air samples from the same locations analyzed by Climate Monitoring and Diagnostics Laboratory (CMDL) except for differences of approximately 5 ppb before 1989 (GAGE lower) and about 4 ppb from 1991 to 1995 (GAGE higher). These results are obtained before applying a factor of 1.0119 to the GAGE/AGAGE values to place them on the Tohoku University scale. The measurements combined with a 12‐box atmospheric model and an assumed atmospheric lifetime of 9.1 years indicates net annual emissions (emissions minus soil sinks) of 545 Tg CH4 with a variability of only ±20 Tg from 1985 to 1997 but an increase in the emissions in 1998 of 37 ± 10 Tg. The effect of OH changes inferred by Prinn et al. 2001 is to increase the estimated methane emissions by approximately 20 Tg in the mid‐1980s and to reduce them by 20 Tg in 1997 and by more thereafter. Using a two‐dimensional (2‐D), 12‐box model with transport constrained by the GAGE/AGAGE chlorofluorocarbon measurements, we calculate that the proportion of the emissions coming from the Northern Hemisphere is between 73 and 81%, depending on the OH distribution used. However, this result includes an adjustment of 5% derived from a simulation of the 2‐D estimation procedure using the 3‐D MOZART model. This adjustment is needed because of the very different spatial emission distributions of the chlorofluorocarbons and methane which makes chlorofluorocarbons derived transport rates inaccurate for the 2‐D simulation of methane. The 2‐D model combined with the annual cycle in OH from Spivakovsky et al. 2000 provide an acceptable fit to the observed 12‐month cycles in methane. The trend in the amplitude of the annual cycle of methane at Cape Grim is used to infer a trend in OH in 30°–90°S of 0 ± 5% per decade from 1985 to 2000, in qualitative agreement with Prinn et al. 2001 for the Southern Hemisphere.
Ozone columns below 147 hPa are derived over the United States from September 2004 to August 2005 from the differences between clear‐sky Aura OMI columns and coincident MLS columns. The mean ...difference from coincident ozonesonde measurements at four USA sites is 0.3 DU with an rms difference of 10.1 DU and a correlation coefficient of 0.67. Semimonthly patterns of the columns over the USA for the summer of 2005 have been produced. The observed columns, as well as Regional Air Quality Forecast (RAQAST) model columns, show high values over the southeastern USA and its surrounding oceans. Changes of these columns exceeding 6 DU in many places were observed between June 17–30 and July 1–16 and the changes reversed in the following two‐week period. Comparisons against calculations from the RAQAST model, as well as correlations with geopotential height changes at 147 hPa, indicate that these changes were primarily related to dynamics.
Measurements of atmospheric chloroform (CHCl3) by in situ gas chromatography using electron capture detection are reported from the Advanced Global Atmospheric Gases Experiment (AGAGE) network of ...atmospheric research stations. They are some of the most comprehensive in situ, high‐frequency measurements to be reported for CHCl3 and provide valuable information not only on clean “baseline” mixing ratios but also on local and regional sources. Emissions from these sources cause substantial periodic increases in CHCl3 concentrations above their baseline levels, which can be used to identify source strengths. This is particularly the case for measurements made at Mace Head, Ireland. Furthermore, these local sources of CHCl3 emissions are significant in relation to current estimates of global emissions and illustrate that the understanding of competing sources and sinks of CHCl3 is still fragmentary. These observations also show that CHCl3 has a very pronounced seasonal cycle with a summer minimum and winter maximum presumably resulting from enhanced destruction by OH in the summer. The amplitude of the cycle is dependent on sampling location. Over the 57 months of in situ measurements a global average baseline concentration of 8.9±0.1 ppt was determined with no appreciable trend in the baseline detected.
We report a steady decrease in the upper stratospheric and lower mesospheric abundances of hydrogen chloride (HCl) from August 2004 through January 2006, as measured by the Microwave Limb Sounder ...(MLS) aboard the Aura satellite. For 60(deg)S to 60(deg)N zonal means, the average yearly change in the 0.7 to 0.1 hPa (approx.50 to 65 km) region is -27 +/- 3 pptv/year, or -0.78 +/- 0.08 percent/year. This is consistent with surface abundance decrease rates (about 6 to 7 years earlier) in chlorine source gases. The MLS data confirm that international agreements to reduce global emissions of ozone-depleting industrial gases are leading to global decreases in the total gaseous chlorine burden. Tracking stratospheric HCl variations on a seasonal basis is now possible with MLS data. Inferred stratospheric total chlorine (CITOT) has a value of 3.60 ppbv at the beginning of 2006, with a (2-sigma) accuracy estimate of 7%; the stratospheric chlorine loading has decreased by about 43 pptv in the 18-month period studied here. We discuss the MLS HCl measurements in the context of other satellite-based HCl data, as well as expectations from surface chlorine data. A mean age of air of approx. 5.5 years and an age spectrum width of 2 years or less provide a fairly good fit to the ensemble of measurements.
Carbon tetrachloride (CCl4) has substantial stratospheric ozone depletion potential and its consumption is controlled under the Montreal Protocol and its amendments. We implement a Kalman filter ...using atmospheric CCl4 measurements and a 3-dimensional chemical transport model to estimate the interannual regional industrial emissions and seasonal global oceanic uptake of CCl4 for the period of 1996–2004. The Model of Atmospheric Transport and Chemistry (MATCH), driven by offline National Center for Environmental Prediction (NCEP) reanalysis meteorological fields, is used to simulate CCl4 mole fractions and calculate their sensitivities to regional sources and sinks using a finite difference approach. High frequency observations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Earth System Research Laboratory (ESRL) of the National Oceanic and Atmospheric Administration (NOAA) and low frequency flask observations are together used to constrain the source and sink magnitudes, estimated as factors that multiply the a priori fluxes. Although industry data imply that the global industrial emissions were substantially declining with large interannual variations, the optimized results show only small interannual variations and a small decreasing trend. The global surface CCl4 mole fractions were declining in this period because the CCl4 oceanic and stratospheric sinks exceeded the industrial emissions. Compared to the a priori values, the inversion results indicate substantial increases in industrial emissions originating from the South Asian/Indian and Southeast Asian regions, and significant decreases in emissions from the European and North American regions.
Assessment of SAGE version 6.1 ozone data quality Wang, Hsiang J.; Cunnold, Derek M.; Thomason, Larry W. ...
Journal of Geophysical Research,
16 December 2002, Letnik:
107, Številka:
D23
Journal Article
Recenzirano
Odprti dostop
The Stratospheric Aerosol and Gas Experiment (SAGE) II V6.1 ozone retrievals are shown to be of better precision at all levels and to be much more accurate than previous retrievals in the lower ...stratosphere below 20 km altitude. A filtering procedure for removing anomalous ozone profiles associated with volcanic aerosol/cloud effects and other identified artifacts in V6.1 ozone is described. The agreement between SAGE and ozonesondes in the mean is shown to be approximately 10% down to the tropopause. Relative to the sondes, SAGE tends to slightly overestimate ozone (less than 5%) between 15 and 20 km altitude and systematically underestimates ozone in the troposphere by approximately 30% in the regions between 8 km altitude and 2 km below the tropopause. The precisions (random errors) of SAGE ozone retrievals above 25 km altitude are estimated to be 4% or better; they are a factor of 10 worse below 16 km altitude. Linear trends in the differences between coincident SAGE and ozonesondes measurement are generally less than 0.3%/yr and not significantly different from zero in 95% confidence intervals. Compared to V5.96 retrievals, ozone trend differences between 20 and 50 km altitude are approximately 0.1%/yr; below 20 km altitude the SAGE II trends are more positive by approximately 0.2%/yr. For the 1984–1999 period, the SAGE II shows a localized ozone loss of −0.4 ± 0.25%/yr (2σ) in the tropics at 20 km altitude. In the lower stratosphere, between 16 and 22 km altitudes, the SAGE shows significant ozone losses in the midlatitudes in both hemispheres during the 1979–1999 periods. The ozone trends range from −0.24 ± 0.18%/yr to −0.77 ± 0.46%/yr (2σ). However, in the 1984–1999 period, the downward trends are smaller (−0.07%/yr to −0.25%/yr) in this altitude range, and the trends in the integrated column from 12 to 17 km altitude in midlatitudes (35°–60°) are not significantly different from zero (0.1 ± 0.6%/yr (2σ)). Averaged over the tropics (20°S–20°N), the ozone column above 15 km altitude exhibit a trend of −0.12 ± 0.08%/yr (2σ).
Ground‐based in situ measurements of 1,1‐difluoroethane (HFC‐152a, CH3CHF2) which is regulated under the Kyoto Protocol are reported under the auspices of the AGAGE (Advanced Global Atmospheric Gases ...Experiment) and SOGE (System of Observation of halogenated Greenhouse gases in Europe) programs. Observations of HFC‐152a at five locations (four European and one Australian) over a 10 year period were recorded. The annual average growth rate of HFC‐152a in the midlatitude Northern Hemisphere has risen from 0.11 ppt/yr to 0.6 ppt/yr from 1994 to 2004. The Southern Hemisphere annual average growth rate has risen from 0.09 ppt/yr to 0.4 ppt/yr from 1998 to 2004. The 2004 average mixing ratio for HFC‐152a was 5.0 ppt and 1.8 ppt in the Northern and Southern hemispheres, respectively. The annual cycle observed for this species in both hemispheres is approximately consistent with measured annual cycles at the same locations in other gases which are destroyed by OH. Yearly global emissions of HFC‐152a from 1994 to 2004 are derived using the global mean HFC‐152a observations and a 12‐box 2‐D model. The global emission of HFC‐152a has risen from 7 Kt/yr to 28 Kt/yr from 1995 to 2004. On the basis of observations of above‐baseline elevations in the HFC‐152a record and a consumption model, regional emission estimates for Europe and Australia are calculated, indicating accelerating emissions from Europe since 2000. The overall European emission in 2004 ranges from 1.5 to 4.0 Kt/year, 5–15% of global emissions for 1,1‐difluoroethane, while the Australian contribution is negligible at 5–10 tonnes/year, <0.05% of global emissions.
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