Bergen Air Quality: Observations and Simulations

Speaker: 
Igor Esau
Affiliation: 
CGR
Seminar Date: 
14. June 2012 - 12:15 - 13:00
Location: 
Lecture room, Ground Floor, NERSC

Atmospheric conditions observed during the cold winter 2010-2011 in Bergen resulted in a case of extreme air
quality hazard. Very high concentrations of the atmospheric pollutants, notably NO2, were measured. Attempts to
reduce their emission rates by policy measures leaded to city life disorganization and severe economic damage.
Using the advantage of turbulence-resolving simulations and extensive meteorological observations in the city,
analysis of the event has been conducted. The simulations (the mesh resolution was 30 m) combined with the
available emission inventory recovered the detailed map of the concentrations. It has been demonstrated that the
slope winds contributed considerably into the air quality hazard. Moreover, it was shown that only a special type
of temperature inversion in the central Bergen area contributes to this event. The strong clear sky radiation cooling
in Bergen causes cold air subsidence along the hill slopes and the near surface northward flow. At the same time
the mean air flow is directed southward as atmospheric soundings reveal. Above the central city area those flows
meet and lock polluted air. The strong radiative inversion, seen both in the model and in the data from Geophysical
Institute, prevent normal air mixing in the deep layer. The inversion top is clearly seen on the photo as the height
of improved visibility.