Package2e (Air Quality)

Instrument PI:     Ulrich Bundke, Forschungszentrum Jülich, (

The P2e Air Quality package is designed to measure the key air quality parameters of aerosols and NO2.

Parameters measured are:

  • Aerosol total number concentration (MAGIC-LP, Aerosol Dynamics)
  • Aerosol size distribution for 125nm – 4 µm (POPS, NOAA, FZJ)
  • Aerosol extinction coefficient at 450 and 630 nm CAPS PMEX (Aerodyne Research)
  • NO2 mixing ratio (CAPS NO2, Aerodyne Research)

The principal sketch of the instrument including the gas flow plan is shown below:  

Fig 1. Schematic of the P2e airflow plan.

Probing air streams are provided through two independent inlet systems. One is dedicated to Aerosol with an upper Cut-off of 3.5 µm and one for NO2. The aerosol inlet (green) is designed using conductive materials (Stainless steel and conductive rubber tubing) to avoid particle losses due to electrostatic deposition at the walls. The Chemical inlet (yellow) for NO2 is made of a non-reactive FEP/PFA material to avoid reactive losses at the wall. A sheath flow system (red) provides particle-free air to protect CAPS mirrors against contamination and supply the POPS instrument with the necessary particle-guiding sheath flow.

For CAPS NO2 the probing flow is dried by means of a Nafion™ dryer. All flows are controlled by means of Mass Flow Controllers (MFC) operated for constant volume flux. Orifices are used to maintain equal shares of flows to different branches of the sampling flow as well as for the sheath flow.

Instrument Performance

Total aerosol number concentration

For Aerosol, the total number concentration is monitored using a MAGIC-LP a water-based Condensation Particle Counter (CPC) of the 3rd generation. It was adapted in cooperation with Susanne Hering from Aerosol Dynamics ( ). The performance of the instrument is demonstrated by Weber et al.  In Figure 1 the cut-off diameter D50 of 5.5 nm of the Butanol based CPC used in the IAGOS Aerosol Package (P2c) (left panel) and the new Magic-LP (right panel) for different operational pressure levels are compiled.

Figure 2. Compilation of the efficiency ratio curves of the Sky-CPC 5.411 (G-CPC) (left) and the MAGIC 210-LP CPC (right) to the FCE reference – at difference operation pressures as a function of the particle size using ammonium sulphate particles. :

Both instruments show an excellent agreement following the 1 :1 relation (see Figure 2) also for different hydrophilic and lipophilic aerosol types well, thus the Aerosol package and the Air quality package total aerosol number-concentration are completely intercomparable.

Figure 3. Comparison of the counting linearity between both CPC types and the Electrometer at different pressure levels for nebulized ammonium sulphate:
Aerosol optical properties (Extinction coefficient)

The Aerosol Extinction Coefficient at 630 nm and 450 nm is measured by using the Cavity Phase Shift principle in Aerodyne CAPS PMex instruments. FZJ has modified and optimized these instruments for airborne usage. The benefit of the CAPS absolute measurement principle is that the instrument does not need calibration. Nevertheless, the performance was tested at different pressure levels by Weber et al. 2021 (

Figure 4. Scatter plots of the extinction coefficients for different external mixtures of light-absorbing and pure scattering aerosols at 630 nm (left) and 450 nm wavelengths (right). The y-axes show the extinction coefficients derived by combining  standard instrumentation (here: A TAP (Tri-colour Absorption Photometer, Brechtel) for absorption- and Nephelometer (TSI 3563) scattering coefficients versus the CAPS PMex monitor direct extinction coefficient measurements). The color code represents the Single scattering albedo ( SSA) of the analyzed mixed aerosol measured at 630 nm wavelength. In addition, an error band of ±10% was added to the 1:1 line
Nitrogen dioxide (NO2)

The CAPS NO2 was tested internally against the P2b instrument using the chemiluminescent measurement principle.

Figure 5. Scatterplot comparing  CAPS NO2 and a Chemiluminescence Instrument
Aerosol Size Distribution

The Portable Optical Particle Spectrometer (POPS) was developed in cooperation with NOAA’s Earth System Research Laboratory in Boulder Colorado. The POPS was modified at Julich for a new gas flow system and a metal housing resisting the pressure difference between the cabin and ambient pressure at cruising altitudes.  The instrument can detect particles within the range of 125nm to 4µm.  The POPS instrument is due to fly as a standalone instrument on the Airbus A350 test aircraft.

The FZJ- modified Portable Optical spectrometer (POPS) was characterized and calibrated using monodisperse polystyrene latex particles.  The following graph shows the calculated instrument response curve superimposed by measurements of different sizes of PSL particles.

Figure 6 shows the Instruments response curve (intensity of particle light scattering as a function of particle size). Superimposed are measurements of light scattering intensities for different PSL (Polystyrene Latex bead particles).


  • The instrument is designed for autonomous deployment over periods of 3-6 Month
  • The instrument operates fully automatically.
  • Operational time is limited by contamination of the CAPS mirrors and liquid supply of the working fluid for the MAGIC CPC.
  • To extend the operational time, the CAPS mirrors were protected by a sheath flow
  • The working fluid is recycled internally.


The instrument has passed all qualification tests and EASA certification STC is in progress.

In cooperation with AIRBUS POPS is operated as standalone instrument at Airbus A350 MSN001.

Figure 7 Laurent ERRERA from L’Union, France, CC BY-SA 2.0 <>, via Wikimedia Commons