Brunke, E.G.

Labuschagne, C.

Mkololo, T.

Scheel, H.E.

English

Brunke, E. G.

Scheel, H. E.

KITopen

Analysis of Ozone Trends at the Cape Point GAW Station, South Africa (34 °S)E-G. Brunke, C. Labuschagne, T. MkololoSouth African Weather Service, Stellenbosch 7599, South AfricaH.E. ScheelKarlsruhe Institute of Technology (KIT), IMK-IFU82467 Garmisch-Partenkirchen, Germany2nd Workshop on Tropospheric Ozone ChangesToulouse, France, 11-13 April  2011Instrumentation:3 analysers Thermo Electron TE 49. Airintakes at 4 m; 14 m and 30 m.Calibration tied to the WMO/GAW scale.Data sets for surface ozone:30 m: 1983 – 2009 with major gap in 1990;4 m: 1997 - 2009Data filtered for background conditionsstored separately.Years of general tendency change: 1989 – 1991,when an overall O3 increase began. Site description:Cape Point (GAW) station: 34⁰ S; 18⁰ E;230 m asl.Situated on a rock face within a nature reserve at the southern point of the Cape Peninsula. Station 60 km south of Cape Town.Shrub (fynbos) vegetation. Winter rainfall. Prevailing winds from SE; however, main large-scale advection from SW. -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40LONGITUDE-60-50-40-30-20-10010LATITUDE 17 19 21-36-34-32Cape PointAFRICAAtlantic      OceanSouth AfricaPrimary BaselineAir AdvectionSOUTH AMERICAIntervals considered for the workshopO3 monthly mean values (1983 – 2009) together with regression curve and long-term trend componentTime series for 30-m air intake, statistical background filter1982 1986 1990 1994 1998 2002 2006 2010010203040Cape Point: Surface Ozone (1983-2009)  O3 [ppb]YEARMonthly means (background)Regression curveTrend30-m air intake, unfiltered dataComparison of anomalies (relative and absolute) with 12-month moving averages (1990 – 2009) absolute anomaly = calculated anomaly + average O3. Ref. = January 2000Annual Trends0.17 (0.14 - 0.20)23.9 (23.7 - 24.1)32.9 %ppb / yr (95%-conf. interval)Intercept Jan 2000 (C.I.) r 2 [%]30-m air intake, unfiltered dataAverage ozone changes according to anomalies of theperiods 1990 – 2009, 1990 – 1999, 2000 - 2009Annual Trends0.17 (0.14 - 0.20)23.9 (23.7 - 24.1)32.9 %– 0.06 (– 0.14 - 0.02)25.1 (24.6 - 25.5)1.8 %0.30 (0.22 - 0.38)24.5 (24.0 - 24.9)31.1 %1 2 3 4 5 6 7 8 9 10 11 1210152025303540CPT: O3  -  Seasonal Variations  O3 (ppb)Month Avg (1995-2008) ±1 std. dev.Cape Point surface ozone:Average seasonal variations (1995 – 2008) with flat July-September maximum and minimum in January.Seasonal Trends: Max. SON, Min. JJAMAMSH autumn0.18 (0.10 - 0.25)23.0SONSH spring0.21 (0.10 - 0.31)26.5Anomalies by season: Overview (1990–2009)Anomalies by season: Regression lines onlyJJASH winter0.12 (0.03 - 0.21)29.2 DJFSH summer0.17 (0.09 - 0.25)17.0Site: CPTAnnual trendsStatist. param. of Lin. Regr.. Intercept (abso-lute) for Jan 2000From monthly mean anomalies (all available data)30-m air intakeStatistical background filtering4-m air intake (all data)2000 - 2009 1990 – 2009 Slope [ppb/yr]Intercept [ppb]r20.17 (0.14 - 0.20)23.9 (23.7 - 24.1)32.9 %0.17 (0.15 - 0.20)23.5 (23.4 - 23.7)39.3 %--------------1990 - 1999 Slope [ppb/yr]Intercept [ppb]r20.30 (0.22 - 0.38)24.5 (24.0 - 24.9)31.1 %0.34 (0.27 - 0.40)24.3 (23.9 - 24.7)44.8 %--------------2000 - 2009 Slope [ppb/yr]Intercept [ppb]r2– 0.06 (–0.14 - 0.02)25.1 (24.6 - 25.5)1.8 %– 0.06 (–0.13 - 0.01)24.7 (24.3 - 25.1)2.3 %– 0.07 (–0.24 - 0.10)25.0 (24.0 - 26.0)0.6 %Seasonaltrends (30 m all)DJFSH summerMAMSH autumnJJASH winterSONSH spring1990 – 2009 0.17 (0.09 - 0.25)17.0 (16.5 - 17.4)52.1 %0.18 (0.10 - 0.25)23.0 (22.5 - 23.4)58.7 %0.12 (0.03 - 0.21)29.2 (28.7 - 29.7)28.8 %0.21 (0.10 - 0.31)26.5 (25.9 - 27.1)48.1 %1990 - 1999 0.08 (–0.14 - 0.29)16.3 (14.9 - 17.6)7.8 %0.27 (0.14 - 0.41)23.3 (22.5 - 24.2)73.4 %0.37 (0.08 - 0.65)30.5 (28.9 - 32.2)52.7 %0.48 (0.18 - 0.77)27.8 (26.1 - 29.4)63.9 %2000 - 2009 0.00 (–0.24 - 0.24)17.9 (16.6 - 19.2)0.0 %– 0.07 (–0.29 - 0.15)24.2 (23.0 – 25.4)6.7 %– 0.07 (–0.28 - 0.14)30.1 (28.9 - 31.3)7.4 %– 0.09 (–0.32 - 0.15)28.0 (26.7 - 29.4)8.7 %Significant positive rates in bold No significant negative rates  Discussion Points• Long-term trends for "all" and "statistically filtered" data coincide.• High and low O3 deviations level each other out.• "Statistical filter" and "CO background filter" yield similar results (not shown here).• For the current study, the major data gap of 1990 was closed using interpoled data from the dynamic harmonic regression fit.• Significant growth rates for the periods 1990 – 2009, and part 1, 1990 – 1999 • Average ozone levels nearly constant during 2000 – 2009• Seasonal trends significant for 1990 – 2009For part 1, 1990 – 1999, only with the exception of DJF (SH summer). Explained by pronounced interannual variability.• O3 increase shows only little seasonal dependency.  ? Supposition of hemispheric processes rather than regional effects ? Concurrent declining CO trend in recent years.? No larger O3 production related to biomass burning ?? Increasing stratospheric influence ?1997 1998 1999 2000 2001 2002051015202530354045505560  O3 (ppb)Year   M   m   pRegression lines for "all" and  "statistically selected" data coincide. 6001997 - 2001Comparison with alternative statistical approachesDifferent calculations of growth rates [ppb/yr]CPT, 30-m air intake, all dataAnomalies Lin. regr. on Lin. regr. on Average rates From differ.as ref. monthly means trend curve derived from Trend_(max - min)(not deseas.) trend curve1990 - 2009 0.17 (0.14 - 0.20) 0.19 0.18 0.22 0.221990 - 1999 0.30 (0.22 - 0.38) 0.37 0.33 0.39 0.382000 - 2009  -0.06 (-0.14 - 0.02) 0.02 -0.03 0.05 -0.051982 1986 1990 1994 1998 2002 2006 20102030Cape Point: Surface Ozone (1983-2009)  O3 [ppb]YEARTrend curveCharacterisation of the air between 4 m and 30 m 30 m4 mCPT, air intake heightsGoal: Estimate of representativeness of the air at the 2 intake heights.Approach: 1/2-h means for the 2 heights, sorted as maximum and minimum.  Calculation of monthly means.  Visualisation of both time series together with linear regression.Result: Between 4 and 30 m the O3 maxima and minima within the 1/2-h periods differ only by 1.5 ppb on average. No indication of different trend behaviour.The 2000-2009 O3 averages over the monthly means for 4 m and 30 m agree within ≈ 0.2 ppb.  During pollution episodes (especially regional fire plumes) differences > 60 ppb between the intakes can occur.Data since 1997Surface Ozone at Cape Point (1983 – 2009)Summary The time series can roughly be divided into 3 parts:1983 – 1989/90: No clear trend behaviour, 2 major gaps.1990 – 2002: Ozone increase statistically significant.2003 onwards: Stabilization. The present study with its periods 1990 – 1999 and 2000 – 2009 partially merges the Cape Point trend observations.Nonetheless, statistically significant growth rates for 1990 – 2009 and1990 – 1999. Maximum annual rate about 0.3 ppb/yr. Different statistical techniques yield compatible growth rate estimates. Long-term trend of surface ozone at Cape Point not critically dependent on air intake height between 4 m and 30 m. Calculated O3 reference mixing ratio for January 2000:23.9 ppb (all data), 23.5 ppb (background).Outlook:Trend estimates based on different monthly percentiles (notably 10th, 25th, 75th and 90th)AcknowledgementsThanks to all who contributed throughtechnical support and data processing,supplementary data,trajectory calculations, discussions,financial support.

Analysis of ozone trends at the Cape Point GAW station, South Africa (34⁰S)

https://publikationen.bibliothek.kit.edu/240088081/3816147

Analysis of ozone trends at the Cape Point GAW station, South Africa (34⁰S)

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