Aerosol monitoring

Aerosols, also known as fine particles or PM (abbreviation for particulate matter), affect the cloud formation and are relevant for climate research. The effect of aerosols on the radiative forcing has yet to be fully researched. Analyses show that the aerosol exposure has decreased in North America over the past 10-15 years, while it remained constant in Europe.

Aerosols are solid or liquid particles in suspension in the air, such as for example soot, mineral dust, salt crystals or ammonium sulfate, with a size ranging between several nanometres and several hundred micrometres. They can affect the atmosphere in two significant ways, by direct and indirect aerosol effects:

  • The direct effect describes the mechanism by which aerosols scatter and absorb solar radiation, thus altering the radiation balance of the earth-atmosphere system.
  • The indirect effect describes how aerosols alter the microphysical (and hence the radiation-relevant) properties, the quantity as well as lifespan of clouds.

The actual effect of aerosols on the atmosphere is still unknown. As of now, not all phenomena have yet been fully understood or identified. In spite of uncertainties, it is assumed that the effect of aerosols in regions with high anthropogenic aerosol levels might be in the same order of magnitude as the effect of all greenhouse gases – albeit with reversed signs. Aerosols slow therfore climate warming.

The radiative forcing of different influencing variables is summarized in the report of the Intergovernmental Panel on Climate Change (IPCC) of 2013. Based on it, the positive effect of greenhouse gases, ozone and water vapour is well explained. The direct and indirect effects of aerosols are usually rated negative, although these statements are tainted with uncertainty.

Aerosol monitoring

The purpose of the Global Atmosphere Watch (GAW) is to determine the spatio-temporal the spatio-temporal distribution of aerosol properties related to climate forcing and air quality up to multi-decadal time scales.. The aerosol monitoring program operated by the Laboratory for Atmospheric Chemistry of the Paul Scherrer Institute (PSI) at the global GAW Station of the Jungfraujoch (3580 m above sea level) is among the most comprehensive ones in the world. Due to the high altitude of the station, the Jungfraujoch is partly located in the free troposphere and is therefore suited to the measurement of the background aerosol. A seasonal cycle is observed for all measured aerosol parameters. This is principally due to the convective transport of the planetary boundary layer toward the Jungfraujoch in the summertime.

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