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Positive trends in Southern Hemisphere observations of carbonyl sulfide
S. Kremser, N. Jones, D. Smale, M. Palm, B. Lejeune, Y.Wang and N. Deutscher EGU General Assembly 2016 19 April 2016
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Why carbonyl sulfide (OCS)?
SO2 Aerosol OCS Aerosol
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Why carbonyl sulfide (OCS)?
10% OCS OCS OCS SO2 Aerosol 90% OCS OCS Aerosol Sheng et al., (2015)
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Why carbonyl sulfide (OCS)?
56% 10% OCS OCS OCS SO2 Aerosol 90% OCS OCS Aerosol Sheng et al., (2015)
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Why carbonyl sulfide (OCS)?
SO2 Aerosol OCS Aerosol OCS Direct ocean flux
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Why carbonyl sulfide (OCS)?
SO2 Aerosol OCS Aerosol OCS CS2 DMS Indirect ocean flux
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Why carbonyl sulfide (OCS)?
SO2 Aerosol Vegetation uptake OCS Aerosol OCS CS2 DMS
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Why carbonyl sulfide (OCS)?
SO2 Aerosol Soil uptake OCS Aerosol OCS CS2 DMS
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Debate…open questions?
In 2002, OCS sources and sinks in balance within the uncertainties Large uncertainties remain, making it a challenge to determine if OCS budget is balanced flask measurements of OCS show no significant trend indicating that OCS is in balance Sinks Source
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What we did… Fourier Transform Spectrometer (FTS) measurements of OCS made at Lauder (New Zealand) and Arrival Heights (Antarctica) Arrival Heights Lauder
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What we did… Retrieve total column OCS amounts for the period 2001 to 2014 derive tropospheric and stratospheric columns Remove annual cycle from the time series - anomalies Apply regression model to OCS measurements to derive best estimates for trends and their uncertainties
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Lauder (45○S, 169.7○E) Overall trend ~4%/decade 6.8±0.4%/decade
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Arrival Heights (77.8○S, 166.6○E)
6.9±1.03%/decade -0.82±2.10%/decade 5.5±4.5%/decade Overall trend ~4%/decade
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Lauder – Tropospheric columns
4.6±0.3%/decade 0.9±0.6%/decade 5.1±1.06%/decade
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Lauder – Stratospheric columns
2.1±0.2%/decade -2.9±0.9%/decade 1.5±0.4%/decade
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Arrival Heights – Tropospheric columns
6.6±1.2%/decade 2.2±1.4%/decade
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Arrival Heights – Stratospheric columns
1.3±0.5%/decade -0.56±2.9%/decade
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Observed trend Causes of observed trend remains to be investigated
Potential causes: Change in tropospheric sources – missing source? Decrease in tropospheric sinks Speed of large scale circulation increased Amount of OCS entering the stratosphere increased
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Summary Clear positive trend over 2001-2014 period in OCS
Overall trend in total columns is dominated by the troposphere: Lauder: troposphere/stratosphere split 76:24 Arrival Height: troposphere/stratosphere split 82:18 Temporal and spatial coherence of changes in trends indicate that causes are likely to be on a hemispheric rather than on a local scale
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