Observational Platforms

Observational Platforms
Observed components
Measured variables

ACTRIS Observational Platforms are fixed ground-based stations delivering long-term high-quality data on a regular schedule and common operation standards by applying state-of-the-art remote-sensing and in situ measurement techniques. 

ACTRIS Observational Platforms are strategically located in diverse climatic regimes and produce high-precision standardized data for free and open access.

ACTRIS Observational components

  • Variables: profiles of aerosol extinction and backscattering, lidar ratio, particle linear depolarization ratio, Ångström exponents; geometrical boundaries of aerosol layers and layer-mean optical properties, columnar spectral aerosol optical depth and sky radiance, particle microphysical and radiative properties
  • High-power aerosol lidar

Optimum: 3-l Raman/HSR lidar with polarization capability (355, 532, 1064 nm), continuous operation

Minimum: 1-l Raman/HSR lidar with polarization (355 or 532 nm), operated on fixed schedule

  • Automatic sun/sky and moon photometer

Optimum: Sun/sky and moon photometer

Minimum: Sun/sky photometer

  Two instruments are required.

  Data are centrally processed at the associated CFs in RRT*.

*RRT = real real-time, within 3 hours after data acquisition


  • Variables: number size distribution (0.01–0.8 µm + other size ranges), light scattering & backscattering coefficients, light absorption coefficient & equivalent black carbon concentration, mass concentration of particulate organic & elemental carbon, particulate elements, particulate organic tracers, non-refractory organic and inorganic aerosols, CCN
  • Minimum instrument set: 3 mandatory + at least 2 specializing variables (out of 9)
    • Mobility Particle Size Spectrometer
    • Integrating Nephelometer
    • Absorption Photometer
    • Thermo-optical method on quartz filters
    • Aerodynamic & Optical Particle Size Spectrometer
    • Condensation Particle Counter
    • Filter-based XRF/PIXE/ICP_OES/ICP_MS
    • Filter-based IC, GC-MS HPLC-MS, LC/MS
    • Cloud Condensation Nuclei Counter
    • Aerosol Mass Spectrometer
    • PSM-CPC
    • Scanning PSM, (N)AIS, N-MPSS

  Data processing at NFs. Data delivery at least yearly. RRT delivery of L0 data recommended.

  • Variables: total water content, liquid water content, effective droplet diameter, cloud droplet number concentration and size distribution, ice crystal number concentration and size distribution , INP number concentration and temperature spectra (outside cloud periods), CCN number concentration, interstitial particle number concentration and size distribution, droplet/ice residual particle number concentration and size distribution, total particle number concentration and size distribution, bulk cloud water chemical composition
  • Minimum instrument set: 3 mandatory (bulk) + at least 2 specializing variables (out of 11)
    • Integrating probes (PVM, PWD)
    • Size-distribution probes (FSSP, FM, CDP)
    • Ice-crystal detectors (photodiode imaging spectrometers, CCD imaging probes, 2D spatial scattering imaging probes, holographic and depolarization particle spectrometers)
    • Filter sampling and off-line analysis of IN
    • Dedicated total and interstitial inlets + scanning mobility particle sizer (for aerosol)
    • Counterflow virtual impactors
    • Bulk water collectors and off-line chemical analysis

  Data processing at NFs. Data delivery at least yearly.

  • Variables: vertical cloud structure, cloud fraction, cloud and aerosol target classification, liquid water content, ice water content, drizzle properties (size distribution, water content, water flux), dissipation rate of TKE (turbulent kinetic energy), liquid water path, integrated water vapour path, temperature and humidity profiles
  • Doppler cloud radar (with polarization)

Optimum: full Doppler spectrum, together with first 3 moments

Minimum: mean Doppler velocity

  • Aerosol lidar

Optimum: high-power lidar with polarization capability

Minimum: low-power lidar/ceilometer (for liquid-cloud detection)

  • Microwave radiometer

Optimum: multi-channel and scanning

Minimum: dual-frequency

  • Doppler lidar (for optimum setup only).

Three instruments are required. All instruments operated continuously.

Data are centrally processed at the associated CF in RRT.

  • Variables: Nitrogen oxides (NO and NO2), volatile organic compounds (non-methane hydrocarbons, oxygenated VOCs, biogenic VOCs, extremely low volatile organic compounds)
      • Optimum: NO, NO2, ozone and relative humidity, J(NO2), NMHC in the C2-C9 range (about 30 compounds), OVOCs in the C1-C5 range (about 10 compounds), BVOCs, aerosol precursors
      • Minimum: NO, NO2, ozone and relative humidity (if needed for analysis), at least 6 VOCs
  • NOx
      • Chemiluminescence detection (CLD)
      • Photolytic conversion with Cavity Attenuated Phase Shift (CAPS) instrument
      • Other NO2-specific techniques
  • VOC
      • Gas chromatography (GC) systems equipped with flame ionization detection (GC-FID) and/or mass spectrometry (GC-MS), on-line or off-line
      • Alternatively: Proton transfer reaction–mass spectrometry (e.g. PTR-MS)

Data processing at NFs.

Data delivery at least yearly. NRT/RRT recommended.

  • Variables: ozone (O3) column, partial column and vertical profile; nitrogen dioxide (NO2) column, partial columns and lower tropospheric profile; formaldehyde (HCHO) column and lower tropospheric profile; ethane (C2H6) column; ammonia column (NH3)
  • Fourier transform Infrared Spectrometers (FTIR)

Optimum: double FTIR (700–5000 cm-1, KBr beamsplitter, InSb and MCT detectors)

Minimum: single FTIR (1900–4100 cm-1, CaF2 beamsplitter, InSb detector; no O3 meas.)

  • UVVIS (DOAS) spectrometers


Minimum: UVVIS/zenith-sky

  • O3 DIAL for optimum setup only

-Optimum: double FTIR + MAX-DOAS or single FTIR + O3 DIAL + MAX-DOAS

-Minimum: double FTIR or single FTIR + UVVIS/zenith-sky

Data processing mainly at NFs (for UVVIS central processing planned).

Data delivery required within 3 months.  NRT delivery recommended.


Observational Platforms