Long-term ozone changes in UT/LS in the northern

hemisphere

Johannes Staehelin,

Christina Schnadt Poberaj,

and Dominik Brunner *

Institute for Atmospheric and Climate Science, ETHZ, Zürich, Switzerland

* Present Address: Empa, Dübendorf, Switzerland

1. Introduction

Ozone is strong greenhouse gas in the UT/LS, but information about long term changes (UT/LS) is very sparse

In the past: information mainly from regular ozonesondes

In this presentation: Analysis of regular aircraft measurements compared with ozonesondes

C. Schnadt Poberaj, J. Staehelin, D. Brunner, V. Thouret, H. De Backer, and R. Stübi: Long-term changes in UT/LS ozone between the late 1970s and the 1990s deduced from the GASP and MOZAIC aircraft programs and from ozonesondes, Atm. Chem. Phys., 9, 5343-5369 (2009)

Presentation

2. Measurements of ozone in upper troposphere/ lower stratosphere (UT/LS)

3. Data treatment

4. Ozone changes in UT from regular aircraft measurements

5. Comparison of UT ozone changes: Regular aircraft vs. ozonesondes

6. LS ozone changes (regular aircraft)

7. Conclusions and outlook

2. Measurements of Ozone in upper troposphere/ lower stratosphere (UT/LS)

a. regular aircraft

GASP (1975-1979) MOZAIC (1994-2001)

Aircraft 4 commercial B-747 and the NASA CV-990 research aircraft 5 commercial Airbus A340

Species O3, H2O, CO, NO, aerosols, and condensation nuclei O3 and H2O

Altitude Range 6-13.7 km 9-12 km

# Flights 6149 14558

# Flight Hours 14200 113008

Ozone Instrument Continuous ultraviolet ozone photometer Dual beam UV absorption

Instrument range 3 to 20000 ppbv 3 to 20000 ppbv

Instrument Precision ± 1% or 3 ppbv, whichever is greater 2 ppbv

Uncertainty 8.4% or 3.3% (depending on diaphragm material).

For very low O3 concentrations: 3 ppbv

± [2 ppbv + 2%]

Temporal Resolution 5s averages every 5 to 10 minutes 1 minute averages

(measurements every 4s)

Measurements from regular passenger aircraft GASP: Global Atmospheric Sampling Program

MOZAIC: Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft Program

Flight RoutesGASP (1975-1979) MOZAIC (1994-2001)

b. Ozonesonde measurements available for comparison with GASP/MOZAIC

Station Country Lat (°N) Lon (°) Total Number Sensor

Uccle Belgium 50.8 4.35 644/1080 BM (*)

Hohenpeissenberg Germany 47.8 11.02 406/900 BM

Payerne Switzerland 49.49 6.57 533/1162 BM

Wallops Island USA 37.93 -75.48 188/970 ECC

BM sonde data have been used with correction factors (CF) applied• Range of allowed CF (BM): 0.9-1.35 (Uccle, Payerne), and 0.9-1.2 (Hohenpeissenberg)•Wallops Island Data normalised using SBUV column ozone information• Sonde data have been corrected for response time of the ozone and pressure sensors

3. Data treatmenta. regular aircraft measurements

• 9% high bias of GASP data removed (caused by a calibration bias (Tiefermann, 1979))

• Spuriously low values (Wozniak, 1979):

Excluded values lower than 10 ppbv in UT and lower than 30 ppbv in LS

• Vertical analysis range

330 hPa–195 hPa (≈ 8.5 km–11.9 km).

In UT, 330 hPa–235 hPa (≈ 8.5 km–10.8 km)

Data treatment of regular aircraft measurements, cont.

• UT ozone not allowed to exceed seasonally variable upper limit in mixing ratio to avoid significant biases of individual averages in regions with limited sample sizes (recent stratospheric intrusions)

Probability Density Function of MOZAIC UT ozone to determine cutoff values:

DJF 80 ppbv

MAM 120 ppbv

JJA 120 ppbv

SON 90 ppbv

b. Treatment of aircraft and sonde data

• Discrimination between tropospheric and stratospheric ozone: At extratropics: Interpolate ERA40 dynamical tropopause information (2 PVU) onto GASP, MOZAIC, and ozonesonde coordinates. In tropics: use thermal tropopause.

• Horizontal averaging:

1. Compute daily means over predefined regions and 10°x10° grid for GASP and MOZAIC UT data

2. Calculate multiannual averages of GASP, MOZAIC and ozone sondes

• Vertical scaling for comparison with ozonesondes: Use potential temperature against tropospause, binning over vertical bands

c. Comparisons of climatologies: determination of changes

• Comparison of long-term changes by aircraft

and ozonesondes:

- Average GASP/MOZAIC data over Europe (42°N–57°N, 5°W–20°E) and USA East (30°N-50°N, 90°W-60°W) and compute differences

- Average ozonesonde data over 1975-79 and 1994-2001 periods and compute

differences

4. Ozone changes in UT from regular aircraft measurements

GASP (1975-1979)

MOZAIC (1994-2001)

spring

spring

fall

fall

winter

winter

summer

summer

Relative UT ozone concentration changesMOZAIC (1994-2001)/GASP (1975-1979), in %

Relative difference between GASP and MOZAIC UT ozone. Data averaged over a 10°×10o grid. Troposph. identification:2 PVU tropopause in extratropics, thermal tropopause in tropics (lat. <35 N). Grey triangles: GASP data biased toward one year (50% from one year), pink triangles: GASP data available from three years only. Hatched boxes: differences statist. sign. at the 95% level. (Differences only where data from at least three years are available for the GASP and number of daily means available for averaging is ten or more.

Winter

Summer

Spring

Fall

Relative change in anthropogenic surface NOx emissions (1975–1979 vs. 1994–2000) in % from RETRO (TEAM-

Model, Schultz, 2007). Emission sources: power generation, industrial, residential, and commercial

combustion, transport, and ships.

Long-term changes of UT ozone (MOZAIC-GASP/GASP, in %) Function of season for regions (W USA, NE USA, ATL, EUR, ME, N IND, N JP, S JP, S

CHINA). Relative differences: only if 10 or more daily regional averages available for GASP and MOZAIC. Vertical bars: 95% confidence intervals of diff.. Bottom rows of

numbers: numbers of daily means available for averaging (upper row: GASP, lower row: MOZAIC). Numbers are colored in orange (red) if GASP or MOZAIC data are biased

toward one year: 50–75% of data from one year (>75% from one year). Grey triangles mark regional averages for which data from three years only are available for averaging.

5. Comparison of UT ozone changes: Regular aircraft vs. ozonesondes

Aircraft measurements vs. European Brewer Mast ozonesondes (Uccle, Hohenpeissenberg, Payerne)

Comparison of ozone changes from aircraft vs. European Brewer Mast sondes

Relative differences of multi-annual mean UT ozone profiles between 1975–1979 and 1994–2001 (%) (1990s–1970s) by aircraft and sonde data over Europe at potential temperature distance from the 2 PVU tropopause. GASP and MOZAIC: averaged over EUR SONDE region. Diff. only if number of daily averages is 10 for all data. Black: MOZAIC-GASP, blue: Uccle, orange: MOHp, red: Payerne. Horizontal bars: 95% confidence intervals of differences.

Winter

Summer

Spring

Fall

Comparison of ozone changes from aircraft with ECC sondes of Wallops Island

(legend same as last picture)

Further questions concerning tropospheric ozone measurements of BM-sondes: comparison Hohenpeissenberg and Payerne with

mountain sites (Jungfraujoch and Zugspitze) PhD thesis Carlos Ordonez (earlier at PSI)

Differences(1991-2004)WinterSpringSummer Fall

Time series and linear trends for surface ozone and sondes Winter Summer

6. LS ozone changes (regular aircraft)(equivalent latitude coordinates)

7. Conclusions and Outlook• Substantial difference in long-term tropospheric ozone

changes between regular aircraft measurements and European Brewer Mast ozonesondes - better agreement for ECC station of Wallops Island (stratospheric ozone: different story)

• UV-sensor believed to be more reliable• UT ozone changes (based on climatologies): Since

second part of 1970s grossly consistent with continental scale ground-based NOx emission changes (RETRO)

• Effect of stratospheric changes ?• Future ?

Ozone production in the troposphere

O

O 2

O 3

sunTerm ina tion

by N O x

In itia tion R O :P ho to lys is o f

O , A ldehydes, H O N O

x

3

O HH NO 3

H

R C H (O H )2

R C H O2 2

H O 2

R C H O2

R C O

R C H (R O G )3

C O

R C H O

Term ina tionby R O + R Ox x

H O2 2

RCH O O H2

OR C O

R C O 2

O

PAN 'sH O 2+

+ H O 2

+

N O 2

+ O 2

+

+

+

or A dd itio n

S ubtractionH O2

O 2+

+ O 2

+ O 2

C O 2

C O 2

+ O 2

H O2

Predicted (ground-based) NOx emissions: The Royal Society, Ground-level ozone in the 21st Century: Future trends, impacts and policy implications, Science Policy

Report 15/08, 2008. UT ozone decrease ?

Stratospheric ozone

Emissions of Ozone Depleting Substances (ODS); black: CFCs; grey: HCFCs

Chemical Ozone Depletion (by ODS)(EESC: Equivalent Effective Stratos. Chl.

Ozone layer:Black: Measurements (60oS-60oN)Grey: Numerical simulations

UV-changes

Ozone changes from stratosphere (at midlatitudes):

Increase ? (Montreal Protocol and enhancement of Brewer/Dobson circulation). Ozone anomalies from model

CMAM and measurements; Cly (Shepherd, 2008)

Future ? UT/LS ozone up or down ?

Long-term UT/LS ozone monitoring important (Activity B1: Global UTLS monitoring approach of IGACO-Ozone and UV radiation Implementation Plan, GAW Report. 182, WMO, Geneva, 2009).

For global coverage for long-term UT/LS ozone monitoring, a coherent approach is needed. This can be accomplished by designing a network integrating current and planned civil aircraft, ground-based (ozone sondes and LIDAR) and UT/LS satellite measurements. In addition, a concept for data quality should be developed making use of the different measurement platforms.

Tasks: - Organize a workshop to discuss current capabilities and identify gaps.

- Aim at developing a strategy to solve the problems.- Prepare assessment report with recommendations.

New project (funding from MeteoSwiss, GAW)

• Close comparison between MOZAIC and ozonesondes (ECC)

• Note: Different EEC ozonesonde types and solute concentrations yield significantly different results in UT/LS ozone (homogenization required !)

Evidence for ozone increase over Europe: 1950-1990

Arosa (Swiss Alps, 1800 msl.): 1950-1990

Emission changes: Fossil fuel related NOx-emissions from continents (TEAM (TNO emission assessm. Model), Pulles et al.)

Acknowledgement

• (Partial) funding from EU-Project RETRO• We thank Andrew Detwiler for providing us the GASP

data • Special thanks to the MOZAIC team for making their

data available to us. The authors also gratefully acknowledge the strong support of the MOZAIC program by the European Communities, EADS, Airbus and the airlines Lufthansa, Austrian, and Air France who have carried the MOZAIC equipment free of charge since 1994.

Total ozone series of Arosa

Time series of ozone monthly means for the UT (left panels) and the LS (right panels) from MOZAIC ozone-measurements. Ozone evolution similar(i) at many sites in northern mid-latit.(ii) to ozone at high mountain sites (strong increase in the second part of the 1990s)Thouret et al., 2006