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Network activity 3:

Standardised measurement protocols, intercomparisons and quality assurance for physical properties of aerosols

Objectives and expected impact

The goal of this network activity will be the standardisation of measurements of physical aerosol parameters. One of the most important physical aerosol parameters is the number size distribution in the size range from 10-500 nm, and in certain cases, to study particle formation, in the size range below 10 nm. The objectives of N3 are therefore:

Objective 1
Harmonisation of measurement protocols and data inversion routines of mobility size spectrometers (DMPS/SMPS) to determine the number size distribution of fine aerosol particle in the range 10-500 nm and regular calibration and technical checks of operating instruments.

Objective 2
Upgrading mobility size spectrometers at selected stations in new and candidate EU countries.

Objective 3
Extension of the range of mobility size spectrometers operated at EUSAAR stations.

Description of work

The aerosol is polydispersed and distributed between particles of diameter spanning several orders of magnitude, from a few nanometers up to several tens of micrometers. A very large fraction of the particle number concentration lies below 500 nm in size.

Common techniques to measure such number size distributions in the fine aerosol particle size range are mobility size spectrometers. The present status is that there is a variety of different commercial and custom-made mobility size spectrometers in use at EUSAAR stations. In general, there is no common data taking protocol (standard measurement procedure) and data processing protocol (standard inversion algorithm) to allow an easy direct intercomparison between the measured number size distributions. Harmonization of both operation modes and inversion schemes will, therefore, considerably improve reliability of the measurements.

Gas-to-particle phase transitions are of considerable importance in connection with the formation and dynamical behaviour of atmospheric aerosols. The occurrence of nucleation events is very difficult to monitor as most size spectrometers operated at research stations cover the size range from 10 to 500 nm. Freshly formed particles have diameters below this size range. Extending the operational size range of size spectrometers below 10 nm will allow for monitoring of the particle nucleation events and put better constraints on particle formation rates. The tasks to meet these objectives are:

  • The activity leader (partner 6) will provide a calibration standard mobility size spectrometer which is always calibrated and should be measuring a “true” size spectrum. This mobility spectrometer will either be sent to a station (especially remote stations) or be used in the calibration facilities of the activity leader for intercomparison with instruments sent to the facility.

  • Mobility spectrometers of EUSAAR stations will be sent to the calibration facilities of partner 6 to be upgraded in soft- and hardware, as necessary. The mobility size spectrometers coming to the calibration facility will be technically checked.

  • The Condensation Particle Counters will be sent at least twice to the calibration facilities for technical checks and calibration of the counting efficiency during the project duration.

  • The data evaluation to determine from the measured mobility size distribution the final number size distribution will be harmonized. Therefore, the routine inversion programs of the different sites will be compared and, if necessary, improved or replaced by common ones.

  • Furthermore, to harmonize the data set of number size distributions, a common data protocol will be developed to be used at all stations. The goal is to obtain a harmonized submission of number size distributions to the EMEP data base.

  • Additional spectrometers from partners 6, 1 and 2 will be upgraded and installed at K-Puszta, BEO Moussala and Kosetice stations.

  • In the calibration facility, a mobility size spectrometer will be modified to extend the size range as much a possible into the range below 10 nm. Therefore, the transfer function of each differential mobility analysers (DMA, core part of the system) must be determined, which is probably different for each DMA due to diffusional particle losses. Additionally, the CPCs must be modified in their operation to be able to detect particle smaller than 10 nm. The CPCs must be calibrated for counting efficiency. A successful modification will be employed at first to a few mobility spectrometers to test this. In case of successful employment, the modification will be extended to all sites in the network.