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

Why carbonyl sulfide (OCS)? SO2 Aerosol OCS Aerosol

Why carbonyl sulfide (OCS)? 10% OCS OCS OCS SO2 Aerosol 90% OCS OCS Aerosol Sheng et al., (2015)

Why carbonyl sulfide (OCS)? 56% 10% OCS OCS OCS SO2 Aerosol 90% OCS OCS Aerosol Sheng et al., (2015)

Why carbonyl sulfide (OCS)? SO2 Aerosol OCS Aerosol OCS Direct ocean flux

Why carbonyl sulfide (OCS)? SO2 Aerosol OCS Aerosol OCS CS2 DMS Indirect ocean flux

Why carbonyl sulfide (OCS)? SO2 Aerosol Vegetation uptake OCS Aerosol OCS CS2 DMS

Why carbonyl sulfide (OCS)? SO2 Aerosol Soil uptake OCS Aerosol OCS CS2 DMS

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

What we did… Fourier Transform Spectrometer (FTS) measurements of OCS made at Lauder (New Zealand) and Arrival Heights (Antarctica) Arrival Heights Lauder

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

Lauder (45○S, 169.7○E) Overall trend ~4%/decade 6.8±0.4%/decade

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

Lauder – Tropospheric columns 4.6±0.3%/decade 0.9±0.6%/decade 5.1±1.06%/decade

Lauder – Stratospheric columns 2.1±0.2%/decade -2.9±0.9%/decade 1.5±0.4%/decade

Arrival Heights – Tropospheric columns 6.6±1.2%/decade 2.2±1.4%/decade

Arrival Heights – Stratospheric columns 1.3±0.5%/decade -0.56±2.9%/decade

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

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