Mission of CiGas

The key-mission of CiGas is to offer current state-of-the art operational support to ACTRIS National Facilities (NFs), operational and exploratory platforms, which are operating instrumentation for continuous long-term measurements of volatile organic compounds (VOCs), condensable vapours and nitrogen oxides (NOx) in the atmosphere. That includes activities to guide research and service development in the field of reactive trace gases and to develop towards future user needs, utilising innovative methodologies. The operational support to ACTRIS NFs is supplemented by tailored services for users from the Global Atmospheric Watch Network (GAW) and other atmospheric observation networks, academia, business, industry, and public services depending on the respective resources.



What CiGas offers

CiGas operates and supports instrumentation and observations for the insitu measurement of reactive trace gases.

The core activities of CiGas are to ensure sustainable and traceable high-quality data and data products of in-situ measured atmospheric reactive trace gases with known uncertainty. These activities include

  • development, testing and implementing advanced measurement technologies and data evaluation algorithms,

  • testing prototypes of gas analytical devices

  • enhancing the competence of the operative personnel by training.

Link with associated communities

Currently, the CiGas units are involved in

CEN (e.g. CEN/TC 264/WG 12, CEN/TC 264/WG 13) and ISO boards to transfer ACTRIS knowledge to a wider user community.


-The cluster lead units FZJV (NMHCs) and FZJN (NOx) are World Calibration Centres (WCCs) for WMO-GAW managing QA/QC processes since years.

-Regular members of WMO-GAW SAG on reactive gases and VOC Expert Group (Empa, IMT, DWD, FZJ)

-GAW-TEC courses

Task Force on Measurement and Modelling (TFMM), EMEP


Activities of CiGas will be linked with associated communities by participating in workshops and overarching intercomparisons. Feedback of that community will further improve Measurement Guidelines (MGs) and Standard Operating Procedures (SOPs). NFs are advised and supported in achieving WMO-GAW labels.

Training and consultancy

In thematic training courses, the necessary expertise for operating an ACTRIS labelled NF will be transferred to participants. Consultation will be provided to users about processes to achieve the ACTRIS label and for setting up observation sites.

Objectives of the training and consultancy will cover all aspects of the MGs and SOPs, QA/QC procedures and data management, as well as for implementing ACTRIS approved new technologies. Guidelines and SOPs are presented during the training workshop, and the use of the up to date guidance is among the quality check of the station audit. The training topics during two dedicated hands-on annual workshops will be defined based on the identified needs of the NFs (observational sites and simulation chambers). The topics could cover a cluster or a sub-cluster of compounds (NMHCS, OVOCs, condensables, NOx) or a specific measurement technique. The annual concept of the training schedule will be developed together with the NFs based on the needs raised.

As new sites will emerge, consultancy and training will be provided to these new NFs during the labelling process.

Beside the site-specific training activities, yearly data QC workshops, the audits, side-by-side intercomparisons, and the topical NF assemblies will serve as an additional training platform.

Training activities will become available for NMHCs and NO in 2022, for OVOCs and biogenic VOCs in 2023, for HCHO and NO2 in 2024 and for condensable vapours in 2025. Training is open to users with physical access. Furthermore, consultancy shall be provided to stakeholders, users and private companies upon request. Current links include the WMO-GAW global and selected regional stations/laboratories which are candidate NFs and participated in trainings on NMHCs and NOx measurements in the past.

Measurement and data procedures and tools

MGs and SOPs will be developed for biogenic VOCs, OVOCs and condensable vapours or updated for NMHCs and NOx, based on proven procedures and methodologies in close cooperation with international bodies (e.g. Global Atmosphere Watch (GAW), National Metrological Institutes (NMIs), AQUILA, EMEP, CEN, ISO), NFs, and users.

Available ACTRIS measurement guidelines



ACTRIS measurement guidelines to come:

-PTR-MS  (expected 2022)


-Condensables (expected 2025)


Measurement and data quality assurance

Data quality and compatibility of ACTRIS trace gas measurements are ensured by station performance tests as parallel offline measurements, side-by-side intercomparisons, on site reference measurements, round robins, and by reviewing the data. Calibration of working standards and target gas and their provision to NFs and users link the measurement of ACTRIS reactive trace gases to primary standards and ensure the state-of-the art traceability international scales.

-Standard gases:

The hierarchy of calibration gases follows the WMO-GAW principles: Each NF shall have a laboratory standard (LS) which is linked to a network-wide reference standard or scale (provided by the central calibration laboratory (CCL) for the specific compound and available through the TC).

Furthermore, NFs operate working standards (WS) for frequent calibration of the analytical instruments. Amount fractions of the WS are linked to traceable laboratory standards (LS) by the NFs.  A target gas (TG), a compound mixture with a matrix close to ambient air, is measured at regular intervals and treated like an unknown ambient air measurement. They serve as a quaternary laboratory standard (LS) in terms of hierarchy of standards linked to the scale. Results of target measurements are used to verify and control the quality of the calibration procedure and the instrument performance.

For each NF it is recommended to operate beside the laboratory standard at least one working standard (WS) and one target gas (TG) and is requested to have the WS and TG checked every two years.

NFs send the WS to the corresponding CiGas units for checking and possibly assigning traceable amount fractions to the target compounds. The WS is calibrated against a primary standard at least by one TC unit. In order to ensure the high quality, a second calibration measurement is envisaged by a second TC unit to verify the results, to eliminate errors in scale transfer and at the same time provide an internal check (intercomparison) between the TC units. Calibration support for working standards is available to NFs .

The same procedure is applicable for target gases (TG), however the TG service is open to users.


The performance of NFs will be checked and controlled by:

i)measuring standards in round-robin experiments: pairs of reference gas mixtures (1 whole air, 1 synthetic) will be circulated among the NFs. Reported results of all NFs will be compared to the reference values.

ii)parallel offline sampling: if needed NFs should sample air in canisters parallel to routine sampling (parallel off-line sampling) and send the canisters to the TC for analysis. Sample canisters can be provided by the TC

iii)central side-by-side (s-b-s) comparisons experiments on field sites or by using EUROCHAMP capabilities: During the s-b-s experiments, the same sample matrix is provided by a central support gas line to each analytical/sampling device using a manifold. The reference amount fraction of the target compounds is set by the corresponding reference instruments at the organising unit. The side-by side comparisons comprise experiments with ambient air as well as tests of artificial prepared test-mixtures and zero gases focusing of possible interfering substances. Corresponding compliance reports will be provided.

iv)target gases: sample target gases in the same way they measure ambient air samples in their systems and report back results

v)Reference instruments: . Depending on needs and availability of suitable instruments, mobile reference instruments will run in parallel to routine measurements at the NFs for a continuous check of calibrations and data quality on-site or during side-by-side intercomparisons. Reference instruments are available only for a sub-set of compounds (e.g. formaldehyde, selected NMHCs, OVOCs, NOx, selected condensable vapors). These instruments will be run in parallel together with the NF instruments.

The work flows are organised by the responsible compound cluster TC unit e.g. NMHCs, OVOCs, Condensable vapours, NOx. The results will be compiled into reports and reflected in the measurement guidelines. Station performance tests are open to users with physical access.


ACTRIS Data Quality Objectives for VOC and NOx from the respective MGs:



Data QA/QC checks:

The data reported by a NF are reviewed following a standardised QA/QC protocol. The submitted time series data are checked in terms of correct flagging of calibrations and instrument malfunction, target gas measurements during round robin, audits and performance exercises, and for outliers.

First level of plausibility tests will filter out the most obvious

At QA/QC annual workshops, the status of the data quality of the NFs will be reviewed using internally developed tools (for instance: @VOC@ for VOCs: https://voc-qc.nilu.no  ), and suggestions for improvements of QA/QC procedures elaborated.

Data review is currently available for NMHC and NO, for OVOCs in the year 2023, for HCHO and NO2 in 2024 and for condensable vapours.

NF labeling and evaluation

CiGas is responsible for defining the labelling criteria and auditing the NF. Audits are for NFs only.

The NFs are visited by the units for audits with the objective to check the performance of the NF according to the minimum requirements set for CiGas NFs, MGs and SOP provided by the audit unit. Deviations from data quality objectives (DQOs) deserve special attention. During an audit, the following will be evaluated:

(1) The sampling and instrument set-up,

(2) the calibration and zero gas systems,

(3) the QA/QC procedures implemented,

(4) the training and instructions sessions,

(5) data from calibration, zero gas, target gas, and standard addition,

(6) the data delivery,

(7) the results from intercomparison exercises,

(8) the uncertainty evaluation,

(9) the logbooks (instrument, measurements, station),

(10) the scientific use of the data and

(11) the overall equipment of the station.

For the performance audit, target gases provided by the auditing unit will be used. Audits will become available for NMHCs and NO in 2022, for OVOCs in 2023, for HCHO and NO2 in 2024 and for condensable vapours in 2025.

Audits are performed by:




Condensables: CiGas-UHEL

New scientific and technological developments

CiGas is involved in improving, testing and developing new instrumentation for assessing the ACTRIS chemical target variables in air. Specifically, the suitability of new instruments for long-term monitoring within ACTRIS and the conformity with the data quality objectives is tested and characterized.

Recommendations will be derived and suggested to the ACTRIS-RI committee to decide on implementing new measurement technologies for achieving high data quality in the ACTRIS-RI together with the NFs at NFs assemblies


Who we are

With FZJV as leading unit, the tasks are shared between six CiGas-units in order to combine complementary expertise. Some activities are duplicated between units to achieve metrological robustness and to provide sufficient capacity. CiGas is structured along specific compound classes forming the clusters

  1. Non-methane hydrocarbons (NMHCs subclassified into anthropogenic and biognic, ANMHCs and BNMHCs, respectivily),
  2. Oxygenated VOCs (OVOCs),
  3. Condensable vapours and
  4. Nitrogen oxides (NOx).

The overall organisational structure is displayed  below.


CiGas Organigram




Forschungszentrum Jülich GmbH, Jülich, Germany


Dr. Ralf Tillmann

Email: r.tillmann@fz-juelich.de

Fon: +49 2461 616963

Leader of CiGas

Leading the activities of NMHCs and contributing to OVOCs

Dr. Katrin Seemeyer

Email: k.seemeyer@fz-juelich.de

Fon: +49 2461 614638

CiGas Project Manager



Empa Swiss Federal Laboratories for Materials Science and Technology, Switzerland


Dr. Stefan Reimann

Email: stefan.reimann@empa.ch

Fon: +41 58 765 4638

Leader of CiGas-CH

Quality assurance of NMHCs and OVOCs using the @VOC@ tool

Implementation of new measurement technologies for VOCs and OVOCs



Institut Mines Télécom Nord Europe, France


Dr. Thérèse Salameh

TS photo

Email: therese.salameh@imt-nord-europe.fr

Phone number: +33 327712625

Leader of CiGas-IMT NE, deputy leader of CiGas

Leading, managing and coordinating activities of OVOCs, and contributing to NMHC and NOx



Deutscher Wetterdienst, Meteorologigal Observatory Hohenpeissenberg, Germany

Contact persons:

Dr. Anja Claude

AC pic

Email: anja.claude@dwd.de

Unit head, contributing to VOC acitivities

Dr. Robert Holla

RH pic

Email: robert.holla@dwd.de

Unit deputy, contributing to NOx acitivities

Main activities:

Contributions to VOC & NOx

  • Consultancy & measurement guidelines
  • target gas measurements
  • side-by-side intercomparisons
  • aspects of data QA/QC
  • linking with associated communities: WMO-GAW, CEN, EMEP


University of Helsinki, Helsinki, Finland

Contact persons:

Unit Head Dr. Silja Häme (silja.hame@helsinki.fi)

Picture Silja Häme

Expert Scientist Dr. Nina Sarnela (nina.sarnela@helsinki.fi)

Picture Nina Sarnela

You can also use our unit e-mail address (actris-api@helsinki.fi) to contact us.

Leading, managing and coordinating activities of condensables (condensing vapors, direct aerosol precursors), and contributing to NMHCs and OVOCs.

Measurement techniques applied:

  • CI-APi-ToF: Direct aerosol precursor measurement systems i.e. chemical ionisation (CI) atmospheric pressure interface (APi) time-of-flight (ToF) mass spectrometer
  • PTR-MS: Proton-Transfer-Mass-Spectroscopy

Main Activities:

  • Provision of measurement guidelines and individual instrument calibrations for nitrate CI-APi-TOF
  • Intercomparison and training workshops
  • NF site performance tests (audits)
  • Method development and mobile reference method provision​​​​​​
  • Consultation in aerosol precursor measurements


Forschungszentrum Jülich GmbH, Jülich, Germany

Contact persons:

Dr. Robert Wegener

Robert Wegener

e-mail: r.wegener@fz-juelich.de

Dr. Max Gerrit Adam

Max Gerrit Adam

e-mail: m.adam@fz-juelich.de


Main activities:

  • Leading and coordinating activities related to the  measurements of nitrogen oxides (NOx) across the national facilities (NFs)

  • Putting in place measurement guidelines, i.e., standard operating procedures (SOPs)

  • Putting in place measurement guidelines, i.e., standard operating procedures (SOPs)

  • NF labelling and evaluation

  • Consultancy and workshops

  • Linking with associating communities