system and performance audit for non methane …€¦ · system and performance audit for non...

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WMO Global Atmosphere Watch World Calibration Centre for VOC’s

WCC-VOC REPORT 2013/1

Report to the World Meteorological Organization

SYSTEM AND PERFORMANCE AUDIT FOR NON METHANE VOLATILE ORGANIC COMPOUNDS

Global GAW Station – Cape Verde Atmospheric Observatory Mindelo, Cape Verde

Status November 2009

Elisabeth Weiss, Stephan Thiel, Rainer Steinbrecher

WMO World Calibration Centre for VOC

Karlsruhe Institute of Technology

KIT/IMK-IFU, Garmisch-Partenkirchen, Germany

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Karlsruhe Institute of Technology

Contact information:

Campus Alpine

WCC-VOC

Kreuzeckbahnstr. 19

82467 Garmisch-Partenkirchen

Germany

Phone: +49 88 21 18 32 17 (Rainer Steinbrecher)

+49 88 21 18 32 38 (Elisabeth Weiss)

Fax: +49 88 21 73 57 3

E-mail: [email protected]

[email protected]

mailto:[email protected]�


VOC- Audit: Regional GAW Station – Atmospheric Observatory Cape Verde, November 2009

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Contents

1 SUMMARY AND RECOMMENDATIONS ........................................................ 1

1.1 General ................................................................................................................... 11.2 System Audit of the Observatory ......................................................................... 11.3 Audit of the VOC Measurements .......................................................................... 11.4 Recommendations ................................................................................................ 1

1.4.1 Recommendation 1 () ................................................................................... 1

1.5 Conclusions ........................................................................................................... 11.6 Summary Ranking of the VOC Audit at the Station ...... ..................................... 2

2 INTRODUCTION ...................................................................................... 33 SYSTEM AND PERFORMANCE AUDIT FOR VOLATILE ORGANIC COMPOUNDS

(VOC) .................................................................................................. 43.1 Description of the Site .......................................................................................... 43.2 Description of the Observatory ............................................................................ 53.3 Staff / Operators .................................................................................................... 73.4 Monitoring Set-up and Procedures ...................................................................... 8

3.4.1 Air Inlet System for VOC ..................................................................................... 8

3.4.2 Gas-chromatographic System ............................................................................. 8

3.5 Operation and Maintenance ................................................................................ 113.5.1 General ............................................................................................................. 11

3.5.2 Sampling and Calibration .................................................................................. 12

3.5.3 Zero and Repeatability Checks, Target Gas ..................................................... 12

3.5.4 Maintenance ..................................................................................................... 13

3.5.5 Corrective Actions ............................................................................................. 13

3.6 Standards ............................................................................................................. 133.6.1 Regulators and Connections ............................................................................. 13

3.6.2 Zero Air ............................................................................................................. 13

3.6.3 Laboratory Standards ....................................................................................... 13

3.6.4 Working Standards ........................................................................................... 15

3.6.5 Calibration of o-VOC and DMS ......................................................................... 15

VOC- Audit: Regional GAW Station – Atmospheric Observatory Cape Verde, November 2009

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3.7 Data Acquisition and Processing ....................................................................... 153.7.1 General ............................................................................................................. 15

3.7.2 Chromatogram Evaluation ................................................................................ 16

3.8 Data Management and Submission ................................................................... 163.9 Documentation .................................................................................................... 17

3.9.1 Technical and QA/QC ....................................................................................... 17

3.9.2 Reports of Results ............................................................................................ 17

3.10 Intercomparison of VOC Standards ................................................................... 183.10.1 Experimental Procedure ................................................................................... 18

3.10.2 Results of the VOC Intercomparison ................................................................. 18

4 REFERENCES ...................................................................................... 235 APPENDIX ........................................................................................... 23

5.1 Individual AnaIysis Results ................................................................................ 235.2 WCC VOC target components ............................................................................ 265.3 WCC VOC Reference ........................................................................................... 265.4 List of Abbreviations and Acronyms ................................................................. 28

VOC- Audit: Regional GAW Station – Atmospheric Observatory Cape Verde, November 2009 1

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1 SUMMARY AND RECOMMENDATIONS

1.1 General A system and performance audit for VOCs was conducted at the Cape Verde Atmospheric

Observatory (CVO) (co-organised by the Chemistry Department, University of York and by

the World Calibration Centre for VOC, WCC-VOC). The audits were conducted in

November 2006 and 2009, respectively. This report summarizes the result of both audits.

The observatory is operated as a global GAW station and analyses air samples directly

collected at the station tower for - amongst others - VOC. The audits were conducted

according to the WMO/GAW guidelines and SOPs for audits as existing. The audit directly

involved the responsible site research scientist, the station manager and the station

director of the observatory. This report is for distribution to the station director, to the GAW

Country Contact, to the WMO/GAW secretariat as well as to the QA/SAC-Germany.

1.2 System Audit of the Observatory

1.3 Audit of the VOC Measurements

1.4 Recommendations

1.4.1 Recommendation 1 () • Important spare parts for the VOC analysis system (e.g. PTV injector) should be

made available on site, including manuals for e.g. Valco valves.

• The technical staff should join GAWTEC-training courses to strengthen the

background knowledge of parameters measured.

1.5 Conclusions The station staff is encouraged to continue further the excellent operation.


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1.6 Summary Ranking of the VOC Audit at the Station ......

Audit Aspect

Adequacy

Comment (0 = inadequate () through 5 = adequate

(■■■■■■))

Access ■■■■■■

Facilities ■■■■■■

Laboratory and office space ■■■■■■

Air conditioning ■■■■■■

Power supply ■■■■■■

General management and operation ■■■■■■

Organisation ■■■■■■

Competence staff ■■■■■■

Air inlet system ■■■■■■

Instrumentation ■■■■■■

Trace gases ■■■■■■

Instrumental performance VOC ■■■■■■

Standards ■■■■■■

Data management ■■■■■■

Data acquisition ■■■■■■

Data processing ■■■■■■

Data submission ■■■■■■

Documentation ■■■■■■

Log books and internal instructions ■■■■■■

Web site ■■■■■■

GAWSIS ■■■■■■


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2 INTRODUCTION

The Cape Verde Atmospheric Observatory (CVO) is managed under the supervision of the

University of York and is operated as a global GAW Station. This station is part of

England's contribution to the World Meteorological Organization Global Atmosphere Watch

(WMO/GAW) programme.

The tasks for the GAW-VOC network have been defined in WMO Report 171 (2007). The

Data Quality Objectives (DQO) and quality control measures set out therein are used for

QA/QC measures as agreed upon by the GAW Scientific Advisory Group for reactive

Gases (SAG RG).

In agreement with the station manager of the CVAO a system and performance audit was

conducted at the station by the WCC-VOC in November 2009.

The audits were performed according the SOP for audits

(http://www.empa.ch/plugin/template/empa/*/55558) adjusted for specific requirements to

VOC analysis in air samples. As a central part of the audit procedure, a VOC

intercomparison based on three travelling standards (TS) of the WCC-VOC was

conducted. Moreover, the whole measurement set-up as well as data processing and

quality assurance measures were reviewed.

http://www.empa.ch/plugin/template/empa/*/55558�


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3 SYSTEM AND PERFORMANCE AUDIT FOR VOLATILE ORGANIC COMPOUNDS

(VOC)

3.1 Description of the Site The following information about the CVO (site description as well as the description of the

observatory) is mainly taken from the corresponding web site web sites

(http://www.ncas.ac.uk/index.php/en/cvao-home) and the GAW Station-information-system

GawSis (http://gaw.empa.ch/gawsis).

Name: Cape Verde Atmospheric Observatory (CVO)

Function: Global station in WMO RA I – Africa

Location: 16.848 °N, 24.871 °W, (10 m asl) Time Zone: UTC-1

The Republic of Cape Verde is an island country, spanning an archipelago of 10 islands

located in the central Atlantic Ocean, 570 kilometres off the coast of Western Africa. The

islands of Cape Verde as well as its position in front of the African coast are shown in Fig.

3-1. The Cape Verde Atmospheric Observatory is located on the Island São Vicente at

Calhau on the NW facing coast line, with the prevailing trade winds blowing directly off the

ocean. The position of the CVO is also marked in Fig. 3-1.

http://www.ncas.ac.uk/index.php/en/cvao-home�

http://gaw.empa.ch/gawsis/reports.asp�

http://en.wikipedia.org/wiki/Island_country�

http://en.wikipedia.org/wiki/Archipelago�

http://en.wikipedia.org/wiki/Atlantic_Ocean�

http://en.wikipedia.org/wiki/West_Africa�


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3.2 Description of the Observatory The Cape Verde Atmospheric Observatory (CVO) was built in 2006. The station is built on

volcanic rock, ca. 50 m from the sea shore with no vegetation around. There are no

habitations within a 2 km radius; the nearest public road is 1.2 km downwind. The

prevailing wind is from the NE from the open ocean bringing air masses from the tropical

Atlantic and from the African continent. The main laboratory is housed in a converted 40ft

shipping container, air conditioned with instruments to carry out the measurements. A

second 20ft container is available for ancillary use. The station can be accessed by an

unpaved dead-end road. Local traffic is negligible. The site covers an area of about 1200

m² which is fenced and guarded (24 h during weekend, 6 pm to 6 am during the week).

The station has a 10 m and a 30 m tower with scaffolds, a storage container and an (Fig.

3-2).

Location of the Cape Verde Atmospheric Observatory within the Islands of Cape Verde

Fig. 3-1: Map showing the location of Cape Verde Islands and the location of the Cape Verde Atmospheric Observatory. (http://ncasweb.leeds.ac.uk/capeverde/index.php?option=com_content&view=article&id=48&Itemid=55)


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The station is part of a bilateral German-UK initiative for long-term observations, ground-

and ocean-based, in the Eastern North Atlantic Ocean region which is quite tropical. It

links several programmes such as the international programme SOLAS, the EU-funded

TENATSO (Tropical Eastern North Atlantic Time-Series Observatory) project, and the

German SOPRAN (Surface Ocean Processes in the Anthropocene) project.

The CVO was set up to advance understanding of climatically-significant interactions

between the atmosphere and ocean. Table 3-1 gives an overview of parameters

assessed at CVO including the timescale of their measurements.

Table 3-1: Measurement program at the Cape Verde Atmospheric Observatory.

Measurement Species Instrument Timescale of measurements

Ozone UV Absorption TEI 49c October 2006 – present

CO UV Fluorescence, Aerolaser 5001 October 2006 - present

NO, NOx, NOy Chemiluminescence, Air Quality Design Inc October 2006 - present

Meteorological data at 4m, 10m and 30m Automatic Weather Station October 2006 - present

NMHCs, DMS, OVOCs Dual channel GC-FID October 2006 - present

Halocarbons GC-MS May 2007 - present

Chemical characterisation of aerosol PM10, PM2.5, PM1

HiVOL Sampler, Digitel DHA-80 subsequent AAS, PIXE, thermographic methods, CE-MS, GC-MS….

November 2006 - present

Fig. 3-2: Picture of the Cape Verde Atmospheric Observatory Cape Verde, dominated by the 30m tower for air sampling. (http://ncasweb.leeds.ac.uk/capeverde/)

30 m tower

10 m tower

http://www.solas-int.org/�

http://tenatso.ifm-geomar.de/�

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Measurement Species Instrument Timescale of measurements

Physical characterisation of aerosol DMPS (3-900 nm) November 2006 - present Physical characterisation of aerosol 5 stage Berner impactor May 2007 - present

BrO/IO/NO LP-DOAS November 2006 - June 2007

BrO/IO/NO MAX-DOAS December 2006 - present

JO1D Radiometer Jan-Feb 2007 May 2007-present

CH4, CO2, N2O, CO, SF6 ratio of O2/N2, and Ar/N2 isotope ratios of 13C/12C and 18O/16O of CO2 and O2

Flask sampling January 2007 - present

Cloud cover Ceilometer January 2008 - present Leachable Fe, Mn, Al, NO3, PO4, amino acids, total metal concentration

Filters, XRF November 2007 - present

Solar radiation Spectral Radiometer April 2008 - present

O2, N2, SF6, CH4, N2O Gas Chromatograph June 2008 - present

CO2 NDIR June 2008 - present

O2 O2 Paramagnetic instrument June 2008 - present

Comment The Cape Verde Atmospheric Observatory fulfils the infrastructural requirements

needed for a global GAW station. The GAW laboratory and the adjacent rooms are

clean, orderly and in good shape. They provide ample space for the instruments and

related infrastructure. All support devices, such as gas cylinders, are kept in the same

environment. There is currently no need for suggesting modifications.

3.3 Staff / Operators The responsibility for the trace gas monitoring programme at the CVO GAW station lies in

the hands of Lucy Carpenter and Alastair Lewis who have the function of the station

directors. Luis Silva Mendes Neves works as a station manager. Katie Read as the Site

Research Scientist served as station contact for the audits. Contacts and positions of

these people who where all involved in the audit are summarised in Table 3-2. The audits

were performed by Rainer Steinbrecher and Stephan Thiel from the WCC-VOC.


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Table 3-2: Staff responsibility for the VOC-measurements at the Cape Verde Atmospheric Observatory

Name Position and duty Telephone E-mail

Katie Read Responsible Site Research Scientist +44 190 443 2565 [email protected]

Luis Silva Mendes Neves Station Manager +238 93 2822 [email protected]

Lucy Carpenter & Alastair Lewis Station director +44 190 444 2526 [email protected];

[email protected]

Luis Mendes gained his professional experience within 4 years of work at CAO, dated by

the time of the audit. During this time his knowledge has been supported by Katie Read as

well as the station directors working with VOC since several years.

Comment It is recommended, that Luis Mendes is going to join a GAWTEC-training course to

become more familiar with GAW.

3.4 Monitoring Set-up and Procedures

3.4.1 Air Inlet System for VOC The air-inlet for gas sampling is installed at 10 m above the ground and free accessible at

360° with no other tubing around. The tubing is made out of stainless steel. Prior to VOC

analysis the sampling air passes a TEFLON in-line filter (SAVILLEX; i.d. 5 cm). The

ambient air is sucked through the manifold with a KNF Neuberger pump at a flow rate of

100 ml/min. Further downstream the ambient air is dried to a dew point of -28 °C using two

condensation traps. The condensation traps are changed on a weekly basis.

3.4.2 Gas-chromatographic System The gas-chromatographic (GC) system for the analysis of NMHC is carried out with an

Agilent 5890, which was installed in 2006. The GC is equipped with two flame ionisation

detectors (FID) from Agilent. The detectors work at a temperature of 250 °C with no

additional make-up gas.

For the separation of VOCs in air samples, two capillary column are installed which are

used in parallel without a pre-column. The specifications of the two separation columns are

listed in Table 3-3.






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Table 3-3: Used separation columns for the VOC analysis at CVO and their characteristics.

Type / Manufacturer

Installed since

Dimension (length, i. d.) Characterisation / Packing

“Al2O3 PLOT Column” Agilent 2005 50 m

0.53 µm Al2O3/KCL-deactivated PLOT column > separates hydrocarbons mainly in

terms of increasing boiling point

“LOWOX Column” Agilent 2005 10 m

0.53 µm High polar column, separates o-VOC mainly in terms of increasing polarity

For both columns the same temperature program is applied during VOC analysis and

detailed in Table 3-4.

Table 3-4: Temperature program for both columns used in VOC analysis at CVO.

Column Temperature program

PLOT Column & LOWOX Column

40 °C for 18.5 min 40 °C to 110 °C at a rate of 13 °C/min 110 °C to 200 °C at a rate of 8 °C/min

200 °C for 25 min 200 °C to 40 °C in one step > 40 °C = standby temp.

As carrier gas Helium (He) is in operation (purity of 99.999 %) and is treated with an

“Agilent purifier” before it enters the GC. The carrier gas flow rate is 22.3 ml/min per

column. The injection of the gas-sample onto the separation columns is achieved by a

“Programmed Temperature Vaporizing” (PTV) Inlet. Sketches of the instrument set-up

both for sampling and analysis mode are shown in Fig. 3-3.


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Fig. 3-3: Sketch of the VOC-measurement set up during sampling and analysis mode used at CVAO.

For the gas sampling, two switching valves (VALCO) with each 6 ports are employed

(indicated in Fig. 3-3 as “autosampler valve” and “sampling valve”). The valves are

controlled by a VALCO-valve units. The tubing diameter of the whole set-up in general is

1/16” and all valves are generally heated to 40 °C. Fig. 3-4 shows the sampling valve

configuration during sampling mode respectively during analysis mode.

Fig. 3-4: Configuration of the sampling valve in sampling mode (left) and in analysis mode (right) which is applied during VOC-analysis at CVAO.

The switching of all the valves as well as the start and stop signals for analysis are

handled with electronic signals from a control software (Agilent). The GC-settings are

Sampling Mode

Helium out

Helium in

Sample in

Sample out

Inject or bot t om

Inject or t op

Sampling Mode

Helium out

Helium in

Sample in

Sample out

Inject or bot t om

Inject or t op

Aut osampler Aut osamplervalve

Condensat ion t rap

MFC4

Inject or boxMFC2

Sampling mode

Pump

MFC3Dilut ant flow

N2 in

Analysis mode

Inject or box

He in

2-posit ion Sampling valve


FID

FID Comput erColumns

Aut osampler Aut osamplervalve

Condensat ion t rap

MFC4

Inject or boxMFC2

Sampling mode

Pump

MFC3Dilut ant flow

N2 in

Analysis mode

Inject or box

He in



FID

FID Comput erColumns

Helium in

Analysis Mode

Sample in

Sample out

Inject or bot t om

Inject or t op

Helium out

Helium in

Analysis Mode

Sample in

Sample out

Inject or bot t om

Inject or t op

Helium out

Analysis Mode

Sample in

Sample out

Inject or bot t om

Inject or t op

Helium out


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coordinated by the software “CHEMSTATION” (Agilent). This software also allows a fully

automated run of the whole procedure of VOC analysis. Fig. 3-5 shows an example

chromatogram resulting from the analysis of a laboratory VOC standard with the above

described system set-up and parameters.

Fig. 3-5: Example chromatogram of a VOC standard analysed at CVO.

Comment The GC system represents state-of-the-art instrumentation and is well suited for high-

quality VOC measurements. This is proofed by the chromatogram shown in Fig. 3-5

with its good separation of the GAW NMHC target components (see Table 5-4 in the

appendix).

3.5 Operation and Maintenance

3.5.1 General The Cape Verde Atmospheric Observatory is usually manned by one permanent

employee. This person is mostly present during working hours from 9:00 am to 5:00 pm on

working days.

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At the time of the audit there was no opportunity for remote instrument control.

3.5.2 Sampling and Calibration All tubing, gas cylinder lines and connections are regularly checked for leaks. At the time

of the audit all the tubings and connections were in orderly and tight manner.

3.5.2.1 Sequence of Injections

Standards, blanks and samples are usually analysed in the following order during normal

operation at CVO:

• 2 Blanks

• 2 laboratory standards

• 2 Blanks

• 60 air samples

• 2 blanks

• 60 air samples

Ambient air samples are taken every hour for 10 min. The calibration of the instrument with

the laboratory standard works automatically and is performed every analytical cycle of 120

air samples (approx. every 5 days). The laboratory standard for this has been in use since

April 2006. For calibration procedures a laboratory standard is in operation, a working

standard is not in use at CVO.

3.5.3 Zero and Repeatability Checks, Target Gas A blank check is automatically performed at CVAO every 2.5 days, every 60 samples.

Pure nitrogen is used for this and is provided from a compressed gas cylinder.

The repeatability of measurements is checked regularly, analyzing 3 identical laboratory

standard samples. The last repeatability check yielded a standard deviation smaller than

5 % for the relative peak area (with n = 3). The obtained results are within the control limits

of the DQOs for precision of 5 %.

To observe the linearity of the detector response as well as the consistency of the

response curve an abundance range test is performed once a year. For this test 6

concentration levels of a standard are measured in dependence of the sample volume.

The last abundance range test performed resulted in a linear regression coefficient (r2) of

1.00 for a 6 level calibration after a linear fit was done. This result lies well in the range of

the control limits were a r² down to 0.95 is acceptable.


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Comment Results of the different checks indicate a very good analytical system performance.

The recommended checks are carried out on a regular basis.

3.5.4 Maintenance Maintenance of the VOC analyzing system is normally conducted as a bimonthly

inspection. Apart from this, the inlet filter is changed on a monthly basis and the

condensation trap on a weekly basis. Gas cylinders are changed on demand and the

instrument is checked daily for characteristic parameters. Other maintenance operations

are only carried out upon demand (e.g. indicated by identified leakages, retention time

shifts, peak shape alterations and so on).

3.5.5 Corrective Actions In case of instrument drift no corrective action are made at CVO. In case of instability,

baseline noise and/or peak shape degradation the instrument is checked to identify the

reason for the instabilities. Data obtained with an obvious malfunction of the instrument are

flagged. After instrumental malfunction or repair, the routine operation is continued after

additional checks for consistency of the response factors and new calibration of the

instrument.

3.6 Standards

3.6.1 Regulators and Connections The pressure regulators used on the high-pressure cylinders are two-stage and out of

stainless steel. The tubing from the cylinders to the valve consist of stainless steel 1/8”.

3.6.2 Zero Air For Blank checks pure Nitrogen (purity 99.999 %) is used as Zero Air at CVAO, supplied in

compressed gas cyclinders.

3.6.3 Laboratory Standards The laboratory standard is stored in the laboratory beneath the GC. The standard is

manufactured by Apel Riemer (S/N: CC 236351) containing 54 NMHC compounds with a

mol faction range from 0.5 to 12.00 µmol/mol and a specified uncertainty of + 5-7 % as

shown in Table 3-5. Since November 2008 a NPL Ozone precursor mix calibration

standard D838940 was used which was then replaced in February 2012 with D860619.


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Acetylene was not stable in the Apel Riemer calibration standard and data had to be

adjusted accordingly.

Table 3-5: Laboratory Standard from Apel Riemer (S/N: CC 236351)

Compound Concentration [ppmv]

Uncertainty [%] Compound Concentration

[ppmv] Uncertainty

[%] ethene 5.35 7 3-methylpentane 1.13 5

acetylene 6.48 7 2-methyl-1-pentene 0.83 5 ethane 11.83 7 hexane 2.85 5

propene 2.19 5 t-2-hexene 0.46 5 propane 10.56 5 c-2-hexene 0.87 5 propyne 4.86 5 methylcyclopentane 0.89 5

i-butane 4.73 5 2,4-dimethylpentane

0.9 5

i-butene 3.14 5 benzene 1.86 5 1-butene 2.34 5 cyclohexane 0.5 5

1,3-butadiene 2.28 5 2-methylhexane 0.9 5

butane 9.05 5 2,3-dimethylpentane

0.44 5

t-2-butene 1.06 5 cyclohexene 0.82 5 c-2-butene 2.26 5 3-methylhexane 0.85 5

1,2-butadiene 5.39 5 1-heptene 2.13 5 i-pentane 6.87 5 heptane 4.02 5 1-pentene 1.1 5 methylcyclohexane 0.94 5

2-methyl-1-butene 1.12 5 2,3,4-trimethylpentane

0.45 5

pentane 8.13 5 toluene 2.72 5 Isoprene 4.42 5 2-methylheptane 0.46 5

t-2-pentene 0.88 5 4-methylheptane 1.11 5 c-2-pentene 2.11 5 3-methylheptane 0.89 5

2-methyl-2-butene 0.92 5 octane 0.49 5 2,2-

dimethylbutane 2.16 5 ethylbenzene 0.9 5

cyclopentene 0.89 5 m-xylene 1.32 5 cyclopentane 0.94 5 p-xylene 0.52 5

2,3-dimethylbutane

1.65 5 styrene 0.49 5

2-methylpentane 0.91 5 o-xylene 0.47 5

The stability of this standard is guaranteed for one year by the manufacturer. It has been

compared with other standards from Apel Riemer on a regular basis (every 1 – 2 years) as

well as its regularly re-calibrated by the CCL.


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3.6.4 Working Standards A working standard is currently not in use at the Cape Verde Atmospheric Observatory.

3.6.5 Calibration of o-VOC and DMS VOC with oxygen (o-VOC) and dimethylsulfid (DMS) are calibrated by means of a

permeation device. The permeation tubes containing the VOCs are kept in heated blocks

(40 °C). The containers with the tubes are flushed at a constant flow rate 100ml/min. The

weight loss of the tubes is determined every two-three months and the emission rates are

calculated. 5-point calibrations are carried out to determine detector response with toluene

as a check of the technique. The toluene response of the FID from the permeation system

is then compared to that of the laboratory standard. At present no reference standards are

available as a CCL is not established yet.

3.7 Data Acquisition and Processing

3.7.1 General Data acquisition of the gas chromatographic signals and parameters is carried out using

the “Agilent” software “CHEMSTATION A.10.02”. As instrument parameters the Sample

flows in and out and the cold trap temperatures are recorded. The analysis of the

measured sample as well as the calibration is also automatically carried out by the

software “CHEMSTATION”.

The quality of measurements is normally assessed by manual visualisation by the operator

of the GC-System. The instrument logbook is also considered as part of the data validation

process as possible bad data resulting from instrument failure can be backtracked there.

Data filtering is based on the laboratory temperature. Outliners are then manually identified

and flagged in the database. As a reference for this “flagging” the detection level of the GC

(< 5 pptv) is used.

Time series plots for different time intervals are also available for long-term observation of

the system performance at the CVO.

The final data validation is done by Katie Read in York.

Comment Data acquisition of system parameters and data processing reflects the state-of-the art

at CVO.


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3.7.2 Chromatogram Evaluation The chromatogram evaluation in the first step is performed with “CHEMSTATION”. Each

peak in the chromatogram is labelled with the retention time and its name. GAW VOC

target compounds analysed show a very good separation from other compounds (Fig. 5-

1). If partial overlap occurs, an automated vertical split of the peaks to the baseline is

carried out. The peak integration of all peaks is always performed manually. Major

interferences have so far only been observed with n -pentane, and some other non GAW

target compound (see Fig. 3-5).

The chromatograms itself as well as the analysis report is stored. The report includes

additional information of the peak area of each detected peak and its height. All these

parameters are used for regular data quality control and the chromatograms are regularly

inspected by an operator. Typical values for chromatogram-characteristics are listed in

Table 3-6.

Table 3-6: Typical chromatogram characteristics obtained from the analysis of VOC-flask-samples at CAL Boulder.

Chromatogram characteristic Typical value

Peak Area [pA x min] 2 - 100

Peak Hight [pA] 20-25

Baseline noise level [pA] 0.02

The calculation of the reported mole fractions is based on the peak area of the detected

analyt. A baseline reset either manually or automatically has not yet been necessary.

Column regeneration is performed every 30 runs through blank runs (see section 3.5.2.1).

Comment The chromatogram evaluation is performed in a highly sophisticated way at CVO.

3.8 Data Management and Submission There are provisions for redundant, off-site data storage at the Cape Verde Atmospheric

Observatory. A computer back up on a hard drive is performed every week with two

copies. One is send to York and one stays at the site. The VOC data sent to the World

Data Center of Greenhouse Gases (WDCGG)and available from the corresponding

website (http://ds.data.jma.go.jp/gmd/wdcgg/).


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Comment The data backup policy and data submission to the WDCGG of the CVO is exemplary.

3.9 Documentation

3.9.1 Technical and QA/QC As part of the system audit, the documentation for QA/QC-procedures was reviewed.

Instrument manuals are available at the laboratory.

Field logbooks were kept in the laboratory and were found to be in orderly manner. The

books were kept both hand-written and electronically. At the time of the audit, they were

found to be up-to-date. Instrument logbooks were also available in the laboratory. Now

central electronic logbook where all maintenance is recorded is maintained and can be

accessed from anywhere using a username and password.

Comment It is highly recommended to have the WMO GAW Measurement Guidelines also

available at the station as the CVAO works as a global GAW station.

Additional to the field logbooks there are standard operating procedures (SOP) available

for the use of the instruments in the laboratory as well as a check list for inspection which

is controlled every day.

Comment The existence of SOP’s for the correct measurement is quite important and well done

by the lab.

At the CVO QC data forms or control charts as well as QC and field shields were not used

by the time of the audit. QA/QC at the time of the audit consisted of thorough manual

checking of the data, removal of outliers, checking and application of blank data, removal

of data where instrument was suspect. For checking detector response stability the

benzene and toluene peaks on both columns are checked for changes in sample volume

and consistency of the system. As a site QA coordinator works Alistair Lewis and he

normally reviews data summaries.

Comment QA/QC Procedures at CVO is in orderly manner.

3.9.2 Reports of Results


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A list of publications is available on the corresponding Gawsis Web-page

(http://gaw.empa.ch/gawsis/) or from the CVO web-site

(http://www.ncas.ac.uk/index.php/en/cvao-publications).

3.10 Intercomparison of VOC Standards

3.10.1 Experimental Procedure Three travelling standards of the WCC-VOC and dedicated pressure regulators were sent

to CVO. They were stored at the same location as the in-house standards to avoid any

temperature influences. Flushing and leak checks were performed after connecting the

standards to the analytical system.

The GC used for analysis of VOC wasn’t modified prior to inter-comparison experiments.

The inter-comparison experiment itself involved the laboratory standard of the station as

well as the three WCC-VOC travelling standards listed in Table 5-6 (part of the appendix).

Each measurement of each standard was repeated five times. All data processing was

performed by the programme manager at the station. Determined mole fractions for each

individual component according to the analysed standard were submitted to the WCC-

VOC including their measurement uncertainties. For the determination of the

measurement uncertainties the error of the quoted response, the repeatability of

calibration measurements within triplicate samples, the repeatability of sample

measurements within 5 samples, the stability of the response, changing blank peak values

as well as the error on peak integration were taken into account by the CVO.

3.10.2 Results of the VOC Intercomparison The individual results reported were evaluated using the WCC-VOC tertiary standard and

the two laboratory standards calibrated to the WCC-VOC tertiary standard.

Prior to sending the travelling standards to the laboratory the WCC-VOC recalibrates all

the standards with its in-house GC system and repeated after the standards return from

the station. All calibrations at WCC-VOC are repeated five times and the mean of these

values is taken as the target concentration. The precision is calculated from the standard

deviation of five measurements multiplied by two (coverage factor 2) to achieve an

extended uncertainty range of approx. 95%. The absolute error of the target concentration

of a compound in the laboratory standards is then calculated taking into account

instrument precision and the specified error of the respective compound in the secondary

http://gaw.empa.ch/gawsis/�


________________________________________________________________________________________________


standard. The mean value of the calibrations for each target compound performed before

the audit and after the audit is then taken as a reference concentration with its respective

error for evaluating the analysis results of the audited laboratory.

It is remarked that only the GAW-NMHC-target components (see section 5.2) as defined in

the WMO Report 171 (http://www.wmo.int/pages/prog/arep/gaw/gaw-reports.html) are

evaluated even if the laboratory reported concentrations for more than those components.

The following diagrams show the results of the evaluation of the results reported after the

audit at CVO. The black dots with the respective error bars indicate the difference from the

reported concentration to the one determined at the WCC-VOC in percent. The bright

green lines stand for the standard’s extended uncertainty (approx. 2σ). As marked in the

graphs the red lines represent the DQOs for the GAW-VOC network.

Results of the direct analysis of the travelling standards

Fig. 3-6: Comparison of the results of WCC-VOC Standard D292363 analysed by CVAO referred to the guaranteed concentrations of the standard.

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


________________________________________________________________________________________________


Fig. 3-6 shows the results of the evaluation of the reported results from the analysis of

travelling standard D292363 at the Cape Verde Atmospheric Observatory.

The analysis of the travelling standard D292363 at CAL-GMD produced quite good results.

The determined concentrations of all components meet the respective DQOs for accuracy.

Apart from Toluene all the components even matched the standards concentrations within

the error limits of the target concentrations. These results indicate that the system is

excellently suitable for VOC measurements in the 2 nmol/mol range. Only the reported

errors for i-pentane, n-pentane and isoprene seem to be relatively high compared to the

ones of the other components. The reason for this may be some small partial overlap with

other compounds eluting nearby (see Fig. 3-5).

Fig. 3-7 displays the results of the evaluation of the reported results from the analysis of

travelling standard D336442 at CVO.


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The results of the analysis of travelling standard D336442 are nearly as good as the ones

from standard D292363. All determined concentrations for the GAW target components

easily meet the DQOs. The concentrations for all these components also nearly match the

standards concentrations within their error limits. It has to be mentioned that the mol

fractions of the components in this standard are up to 15 nmol/mol. This is about seven

times the concentration compared to the other standard D292363. The good results for the

analysis of this standard indicate that the system is suited to work quite well also for high

concentration air samples.

The results of the analysis of travelling standard D336417 are shown in Fig. 3-8. It has to

be noted that this standard contains isoprene below the detection limit of the WCC-VOC

system (0.02 nmol/mol) and is therefore missing in the following graphic.

Fig. 3-7: Comparison of the results of WCC-VOC Standard D336442 analysed by CVAO referred to the recalibrated concentrations of the standard by the WCC-VOC.


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The correct determination of the target mol fractions of travelling standard D336417 is

challenging as they are quite low (0.1 to 1.1 nmol/mol). However, CVO performed quite

well even for this standard. Only the determined concentration for n-butane and toluene

are outside the DQOs. For all other components the determined concentrations match the

standards concentrations quite within the DQOs or even within the error limits. It is

remarked that the reported errors in this analysis are not remarkably higher than in the

analyses of the other (higher concentrated) standards.

Comment Inter-comparison experiments for the analytical system reveal a very good

performance. Only the repeatability of the measurements of the lager NMHCs (mainly i-

pentane, n-pentane and isoprene) could be a little better.

Fig. 3-8: Comparison f the results of WCC-VOC Standard D336417 analysed by CVAO referred to the recalibrated concentrations of the standard by the WCC-VOC.


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4 REFERENCES

WMO, Global Atmosphere Watch, (2007), Report No 171: A WMO/GAW Expert Workshop on Global Long-Term Measurement of Volatile Organic Compounds (VOCs).

5 APPENDIX

5.1 Individual AnaIysis Results Table 5-1: Results of the analysis of travelling standard D292363

reported by CVAO to the WCC-VOC.

Analyt Result (nmol/mol)

Measurement uncertainty (95% confidence)

(nmol/mol) ethane 2.71 0.17 ethene 2.69 0.33

propane 2.67 0.17 propene 2.61 0.18

iso-butane 2.68 0.21 n-butane 2.6 0.18 acetylene 2.63 0.13

trans-2-butene 2.59 0.22 1-butene 2.53 0.24

cis-butene 2.53 0.18 iso-pentane 2.57 0.29 n-pentane 2.6 0.49

hexane 2.58 0.48 isoprene 2.58 0.42 benzene 2.63 0.17 toluene 2.38 0.23

Table 5-2: Results of the analysis of travelling standard D336442 reported by CVAO to the WCC-VOC.



nmol/mol ethane 12.7 0.79 ethene 7.23 0.89

propane 11.97 0.77 propene 2.27 0.16

iso-butane 6.18 0.49 n-butane 10.66 0.76 acetylene 7.7 0.40 cis-butene 3.54 0.25

iso-pentane 7.8 0.88 n-pentane 9.34 1.75

hexane 3.24 0.61 isoprene 5.39 0.88 benzene 2.23 0.18 toluene 2.34 0.18


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Table 5-3: Results of the analysis of travelling standard D336417 reported by CVAO to the WCC-VOC.



(nmol/mol) ethane 1.13 0.07 ethene 0.81 0.10

propane 0.49 0.03 propene 0.27 0.02

iso-butane 0.54 0.05 n-butane 1.1 0.08 acetylene 0.9 0.05

trans-2-butene 0.11 0.01 1-butene 0.14 0.01

iso-pentane 1.5 0.18 n-pentane 0.44 0.08

hexane 0.16 0.03 benzene 0.36 0.02 toluene 0.59 0.10

Fig. 5-1: Ambient air chromatogram at CVO


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Fig. 5-2: Ambient air mixing ratios of selected VOC at CVO in 2007. High VOC levels during a dust episodes.


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5.2 WCC VOC target components The following table gives an overview for the VOC GAW-aim components with the agreed

data quality objectives for both accuracy and precision of the analysis. The agreed list of

these components would normally be longer but up to now it has only been possible to get

reliable, stable standards for these components. The other molecules are even more

reactive and furthermore the analysis of these components is a bit more difficult than the

ones listed in Table 5-4. Until it is not possible to analyze the other components as reliable

as the ones listed in Table 5-4 the WCC-VOC isn’t able to evaluate the measurement of

more of those compounds listed in the following table. The analysis of these components

respectively the results of their analysis is mainly taken into account when an audit is

appraised and the final evaluation of the audited station / laboratory is set. Table 5-4: VOC GAW target components with the agreed

data quality objectives for both accuracy and precision of the analysis.

Compound Accuracy Precision

Ethane 10% 5%

Ethyne 15% 5%

Propane 10% 5%

Iso-/n-Butane 10% 5%

Iso-/n-Pentane 10% 5%

Isoprene 20% 15%

Benzene 15% 10%

Toluene 15% 10% Mol fraction

< 0.1 nmol mol-1 ± 20 pmol mol-1 ± 15 pmol mol-1

5.3 WCC VOC Reference The WCC-VOC has one laboratory standard containing VOC mol fractions in Nitrogen.

The accurate concentrations of the single VOC’s are certified by NPL which works as a

central calibration laboratory. The composition of the standard as well as its uncertainty is

listed in Table 5-5. Compounds in bolt are part of the GAW aim components for VOC

analysis. This laboratory standard is itself used as a TS of the WCC-VOC.


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Table 5-5: NPL-certified D292363 VOC standard at WCC-VOC. The cylinder contains VOC’s in pure nitrogen. The measurement of this standard is the basis for the recalibration of the travelling standards D336442 and D33617.

Compound Nominal

value /ppb

Uncertainty 2σ/ppb

Overall uncertainty 2σ

of analysis/ ppb ethan 2,7 0,05 0,08 ethene 2,67 0,05 0,07 ethyne 2,66 0,05 0,05

propane 2,67 0,05 0,11 propene 2,63 0,05 0,07 i-butane 2,68 0,05 0,05 1-butene 2,56 0,05 0,06

1,3-butadiene 2,63 0,05 0,05 n-butane 2,6 0,05 0,05

trans-butene 2,6 0,05 0,05 cis-2-buten 2,56 0,05 0,05 i-pentane 2,59 0,05 0,05 1-pentene 2,55 0,05 0,05 n-pentane 2,63 0,05 0,05 isoprene 2,6 0,05 0,05

trans-pentene 2,5 0,05 0,05 2-methyl-pentane 2,59 0,05 0,05

hexane 2,6 0,05 0,05 benzene 2,62 0,05 0,09

2,2,4-trimethylpentane 2,61 0,05 0,05 heptane 2,56 0,05 0,06 toluene 2,59 0,05 0,25 octane 2,59 0,05 0,05 nonane 2,49 0,05 0,06 α-pinene 2,01 0,06 0,06

Additional to this standard there are two more standards sent to the labs prior to an audit.

These two additional standards are regularly recalibrated by comparison with the analysis

results of the laboratory standard. Table 5-6 lists the nomenclature of all travelling

standards used at WCC-VOC as well as the approximated mol fractions of the VOC’s in

these standards.


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Table 5-6: Travelling standards of WCC-VOC used for measurements at the audit.

Cylinder Number Mol fractions of VOC’s [nmol/mol]

D292363 2,00 – 2,70

D336442 13,50 – 2,00

D336417 1,25 – 0,20

5.4 List of Abbreviations and Acronyms CVAO Cape Verde Atmospheric Observatory

DQO Data quality objective

FID Flame ionization detector

GAW Global atmospheric watch

GC Gas chromatograph

GMD Global monitoring division

KIT Karlsruhe institute of technology

m.a.s.l meter about sea level

MG-VOC Measurement guidelines for volatile organic compounds

N North

NMHC Non-methane hydro carbons

NPL National Physical Laboratory UK

o.d. outer diameter

QA/SAC Quality assurance / Science activity centre

SAG RG Scientific advisory group for reactive gases

TS Travelling standard

UBA Umweltbundesamt

W West

w/w weight per weight

WCC-VOC World calibration centre for volatile organic compounds

WDCGG World data centre for green house gases

WMO World meteorological organisation

system and performance audit for non methane …€¦ · system and performance audit for non...

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