Measuring trace gases at Cape Point GAW: Operation, Data ... · Measuring trace gases at Cape Point GAW: Operation, Data management and QA/QC procedures E-G. Brunke, C. Labuschagne

Templ ref: PPT-ISO-colour.001 Doc Ref no: Air Quality Lekgotla: 6-7 Oct 2014; KZN

Measuring trace gases at Cape Point GAW: Operation, Data management and QA/QC procedures

E-G. Brunke, C. Labuschagne, N. Mbatha, L. Martin, T. Mkololo, G. Coetzee and D. vd Spuy


Measuring of trace gases at Cape Point

Outline of Talk

1. What is Global Atmosphere Watch (GAW) ?

2. Measuring program and a few trace gas results

3. The need for Quality Assurance and Control (QA/QC)

4. Calibration scales, traceability and audits

5. Operation of Station (instrumental parameters)

6. Data Management and Protocols

7. QA/QC Procedures within GAW


What is Global Atmosphere Watch (GAW) ?

• GAW focuses on global networks for GHGs, ozone, UV, aerosols, selected reactive gases, and precipitation chemistry.

• GAW is a partnership involving contributors from 80 countries.

• GAW is coordinated by the Environment Division of WMO/AREP under the purview of WMO Commission for Atmospheric Science (CAS)

• Currently GAW coordinates activities and data from 33 Global stations, 413 Regional stations, and 164 Contributing stations (http://gaw.empa.ch/gawsis/)


Global Atmosphere Watch Central Facilities


The Cape Point GAW Program

summer winter

Wind Roses for Cape Point


Ongoing process to upgrade instrumentation

CO2

Increased demand by modelling community for higher

quality data (reduced uncertainty limits)

CO

Advantages of new CRDS systems:

• Less calibration gas needed • No H2O removal required • Better long-term stability • Higher data resolution Example: Data resolution in the case of CO improved from 4 to 60 data points/hr.


Current GAW Measuring Program Parameters measured:

• Greenhouse gases – CO2; CH4 and N2O

• Other trace gases – CO; O3; SF6 and 222Rn

• Halocarbons: CFCl3, CCl4, CH3CCl3, CCl2F-CClF2

and CCl2F2

• Aerosol optical properties and AOD

• Solar radiation – (UVA, UVB, Global, Total & Diffuse)

• Met parameters: Wind, Pressure, Temperature,

Relative humidity, Rainfall

• Approx. 9 co-operative ventures (national & international)


Regional station network coupled to Cape Point

Most global WMO GAW sites such as Cape Point, have a strong regional network

component. Irene constitutes one of the important GAW regional stations of Cape Point.

Here a Dobson Ozone Spectrophotometer has been in operation since 1989 and ozone

soundings started there shortly afterwards.

Column ozone measurements at Irene

Dobson O3 Spectrophotometer


Irene Ozone Soundings

Since 2012 - Renewed efforts:- added motivation by Tropospheric Ozone ISSUES (Air Quality–SAAQIS ). A new MW31 system replaced the older system and ECC ‘s are flown with the RS92 Vaisala Radiosondes. Recent shift in research focus:- To also include tropospheric Ozone research in the polluted Johannesburg – Pretoria Mega City region.

System : A Vaisala - MW15 Digicora and ECC RS80 radiosonde.

1997 - SAWS joined the USA NASA Ozone program, known as the Southern Hemisphere Additional OZonesondes (SHADOZ- http://croc.gsfc.nasa.gov/shadoz/ ).

1989 - The initial motivation - due to international Protocols and Obligations - made SAWS revive its ozone program, especially in view of the Ozone Layer depletion debates. As such: Dobson Spectrophotometer #089, 1956, in addition to Ozone Balloon Soundings, were activated to “keep a check “ on the Ozone Layer.

http://croc.gsfc.nasa.gov/shadoz/

http://croc.gsfc.nasa.gov/shadoz/


Findings: Irene tropospheric ozone climatology

Tropospheric ozone increases over the southern Africa region: bellwether for rapid increases in Southern Hemisphere pollution?

A. M. Thompson, N. V. Balashov, J. C. Witte, J. G. R. Coetzee, V. Thouret, and F. Posny. Atmos. Chem. Phys., 14, 1–15, 2014, www.atmos-chem-phys.net/14/1/ 2014/, doi:10.5194/acp-14-1-2014.

Ozonesonde records show 20-30% increases in O3 at Irene in the urban- influenced boundary layer (1.5 – 4 km) over a 18 year period. This may be indicative of growing pollution in the SH.

http://www.atmos-chem-phys.net/14/1/2014/






Some Cape Point results: CO2; CH4 and surface O3 C

arb

on

dio

xid

e (

pp

m)

Mixing Ratio & Trend

Growth Rate

Carbon dioxide Mixing Ratio & Trend, and Growth Rate

Year93 95 96 98 00 02 04 06 08 10 12

350

355

360

365

370

375

380

385

390

395

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

Carb

on

dio

xid

e (

pp

m/y

r)

Carbon Dioxide

Meth

an

e (

pp

b)

Mixing Ratio & Trend

Growth Rate

Methane Mixing Ratio & Trend, and Growth Rate

Year83 84 86 88 90 92 94 96 98 00 02 04 06 08 10 12

1550

1600

1650

1700

1750

1800

-5

0

5

10

15

20

Math

an

e (

pp

b/y

r)

Methane

After: Oltmans et al., 2013

Southern Hemispheric O3 Trends


The need for quality control

•Detect small trends (via Data Quality Objectives [DQOs])

•Detect small spatial gradients (e.g. between hemispheres)

•Ensure long-term stability of observations

•Data comparability (on the same scale)

The 2nd International Workshop on Atmosphere Watch in Asia “Greenhouse Gases Monitoring Activities”, Oct. 21-22, 2010

comparability: Measurement results that are metrologically traceable to the same reference standard


Conceptual framework of the GAW quality system

The 2nd International Workshop on Atmosphere Watch in Asia “Greenhouse Gases Monitoring Activities”, Oct. 21-22, 2010

BIPM / NMI Bureau International des Poids

et Mesures / National Metrology

Institutes


Data Quality Objectives (N2O as an example) Instrumental precision Repeatability (2 standard deviations): at least 0.2% ( 0.6 ppb). Future goal: repeatability 0.2 ppb; reproducibility 0.3 ppb.

Relevant range of N2O mole fractions For basic calibrations of the analytical system and for inter-comparisons, 6 (min. 5) different N2O mole fractions between 290 and 350 ppb should be used. This will determine the response curve of the detector (ECD) for N2O.

Uncertainty of ambient N2O measurements The uncertainty associated with ambient N2O measurements can be separated into contributions related to: (i) instrumental precision, (ii) uncertainty associated with the standard scale, (iii) accuracy of the working standards employed at a specific site. Uncertainty will be estimated by inter-comparisons with standards within a round-robin experiment or inter-comparisons as part of a field audit. Such exercises will determine if measurements at different sites and/or from different institutions are on the same scale or not.

For the near future, maximum acceptable uncertainty levels are defined as: 0.5 ppb for the range 310 - 330 ppb, 0.8 ppb for the upper and lower wings. Data having uncertainties larger than 1 ppb (in the range 310 - 330 ppb) and 1.5 ppb (upper and lower wings) will not be accepted for the GAW network. These uncertainties will determine the inter-laboratory comparability of N2O measurements.

Target DQOs in future will request: Maximum uncertainty of 0.1 ppb for the range of 290 to 350 ppb.


• The Agilent GC with micro-ECD posed many analytical challenges since its inception during mid-2007: sensitivity variations and data uncertainty.

• At the beginning of 2011 GC reduced to bare essentials: separate solenoids, 6-way Valco valve, carrier gas directly to column, no makeup, no back flush or O2 removal, column length increased to 8 m.

• WCC-N2O audit conducted under these conditions in Feb 2011: acceptable results.

• Quality of ambient measurements improved after Aug 2011

Cape Point N2O measurement challenges

Current chromatogram

O2

N2O

SF6

SEP 2011

Target gas

[ppb]

Ambient

[ppb]

Average 318.51 322.42

Std dev 0.32 0.46

RStd dev % 0.10 0.14

Count 25 109


Central Calibration

Laboratory (CCL)

WCC-N2O

GAW Stations

Other Stations,

Laboratories

Transfer

of scale

QA/QC:

Audits &

Round

Robin

Exper.

Harmonisation

Traceability of Calibrations and Audits

Manufacturers,

Laboratories

Supply with gas cylinders

Primary Standards

Secondary Standards

Laboratory Standards

Laboratory Standards

Working Standards

Harmonisation

Transfer / Travelling

Standards

Transfer

of scale

Calibration Scales for CO, CO2, CO, CH4 and N2O within GAW

The NOAA CMDL calibration scale (for details: http://www.cmdl.noaa.gov/ hats/index.html) is the standard scale for WMO-GAW. Therefore NOAA CMDL acts as Central Calibration Laboratory (CCL). The scale is based on a series of Primary and Secondary Standards kept at the CCL.

Traceability, calibration gas hierarchy

Lab standards at CPT


RIX Oil-free compressor; making own working standards

Working and lab standards

• Working standards comprise CPT air

(some times spiked) and calibrated

against NOAA lab standards.

• The working standards are used on

average once/every hour - and last

perhaps two years.

• Regular inter-comparisons are carried

out between the lab and the working

standards.

• Lab standards have to be re-analysed

once every three years by NOAA to

ensure that no drift has taken place.

• The primary standards are kept and

maintained in Boulder (CCL) by NOAA.

RIX Oil-free compressor


Importance of regulator types for reliable measurements

• Flush regulator three times prior to performing calibrations to remove memory effects • Analysing sequence: start off with cylinders having low trace gas concentrations first

Checking for any leaks: • Output regulator pressure

drop when closed • Soap solution (Lecksuch)


Quality Control through Audits and Round-Robins

Audit History:

1997 WCC-EMPA (O3)

1998 WCC-EMPA (O3 & CO)

2002 WCC-EMPA (O3, CO & CH4)

2003 WCC-N2O

2005 4th WMO CO2 Round robin

intercomparison

2006 WCC-EMPA (O3, CO and CH4)

2006 WCC-AP (aerosols)

2011 WCC-EMPA (O3, CO, CO2 & CH4)

2011 WCC-N2O

2014 WMO round robin intercom-

parison (CO,CO2, N2O and CH4)

Canisters for which trace gas levels need to be determined


System and performance audits at GAW stations


Checklists and instrumental logsheets

E-logs - also accessible remotely

Check list(s): daily, monthly and quarterly


Ongoing checks: instrumental parameters, raw data

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

01-May 04-May 07-May 10-May 13-May 16-May 19-May 22-May 25-May 28-May 31-May

T_013_A/B

T_223_A/B

140

A/B ratios for Tekran mercury analyser to fall within 10% range

Picarro vacuum pump’s cavity pressure check

Remote access/control

Methane Check chromatogram for baseline stability and peak shape


Lab work requires care and meticulous approach !


480

490

500

510

520

530

540

550

560

570

580

Feb-07 Jun-08 Nov-09 Mar-11 Aug-12 Dec-13 May-15

Mo

le f

racti

on

[p

pt]

Targetgas values for Freon-12[ppt]

2.0

3.0

4.0

5.0

6.0

7.0

8.0

Nov-10 Feb-11 Jun-11 Sep-11 Dec-11 Apr-12 Jul-12 Oct-12

O3

[p

pb

]

Monthly avg zero values for O3_Teco1 [ppb]

Monitoring zero levels of ozone analysers on a daily basis and archiving monthly avgs. The same is done for daily O3 SPAN levels.

?

The importance of target gas values to monitor long term instrumental stability

Monitoring instrumental stability on a monthly basis


Removing dubious calibration values: N2O as an e.g.

Upper and lower N2O calibration gas peak height values (bracketing the ambient levels).


Flask sampling procedure

• Duplicate flask samples are collected

on a weekly basis under baseline

conditions and analysed at NOAA,

Boulder, USA.

• Our in-situ trace gas results (30 min

averages) are submitted on a monthly

basis to NOAA.

• In return, NOAA supplies us with inter-

comparison (ICP) results

(https://om.cmdl.noaa.gov/icp)

Quality Checks via Flask sampling program

Collection of NOAA flask samples


QAC and filtering of annual data sets

CH4 as an example: Importance of seeing the bigger picture

FILTERING: Two 11-day moving percentiles (e.g. 5th and 95th ), each one adjustable by an additional factor, establish lower and upper thresholds, respectively. In this way a narrow concentration band is obtained which essentially represents background data (devoid of local pollution).

Data block jumps mostly analytical


370

375

380

385

390

395

400

405

410

1 31 61 91 121 151 181 211 241 271 301 331 361

CO

2 [

pp

m]

Filtered Cape Point CO2 (2011) 30 min averages

Urban-continental

signal

Filtered data

(marine)

Draw-down events

(continental). Not artefacts !


Halley, Antarctica

Barrow, Alaska Minamitorishima, Japan

Neumayer, Antarctica

Cape Grim, Australia

Cape Point, SA

The primary objectives of the GAW quality assurance system are to ensure that the data in the World

Data Centres are consistent, of known and adequate quality, are supported by comprehensive metadata

and are sufficiently complete to describe the global atmospheric state with respect to spatial and

temporal distribution.

High-quality observational data are required to provide reliable information to policymakers and to ensure

confidence in the broader data use in different applications.

QA/QC Procedures within GAW


Examples: For a detailed description of DQOs for CH4 and N2O along with guidance for the measurements see:

GAW Report No. 185:

Guidelines for the

Measurement of Methane

and Nitrous Oxide and

their Quality Assurance

Similarly, for CO see: GAW Report No. 192.

Guidelines for the

Measurement of

Atmospheric Carbon

Monoxide

GAW Reports at:

http://www.wmo.int/pages/prog/arep/gaw/gaw-

reports.html


Several Measurement Guidelines (MG) or equivalent documents have been prepared in recent years.

143. Global Atmosphere Watch Measurements Guide (WMO TD No. 1073).

146. Quality Assurance in monitoring solar ultraviolet radiation: the state of the

art. (WMO TD No. 1180), 2003.

153. WMO/GAW Aerosol Measurement Procedures: Guidelines and

Recommendations. (WMO TD No. 1178)

160. Manual for the GAW Precipitation Chemistry Programme (Guidelines, Data

Quality Objectives and Standard Operating Procedures) (WMO TD No. 1251),

186 pp, November 2004.

.

183. Operations Handbook – Ozone Observations with a Dobson

Spectrophotometer (WMO TD No. 1469), 91 pp, March 2009..


In general, Measurement Guidelines (MG) leave more flexibility than Standard Operating Procedures (SOP).

Depending on the measurement technique(s), SOPs may be less appropriate than MGs for the work at GAW Global Stations.

Data Quality Objectives (DQO) for GAW Global Stations are driven by scientific needs.

A few lessons learnt


Submission of Cape Point Data

Quality checked data

http://www.esrl.noaa.gov/gmd/ccgg/carbontracker/

http://gaw.kishou.go.jp/wdcgg/

http://www.saaqis.org.za/




Acknowledgements

Local authorities:


THANK YOU !

Documents

Measuring trace gases at Cape Point GAW: Operation, Data ... · Measuring trace gases at Cape Point GAW: Operation, Data management and QA/QC procedures E-G. Brunke, C. Labuschagne