Category 18 April 2019

EUCAARI - aircraft field campaign

Understanding of the existing interactions between air pollution and climate was an ambitious aim of EUCAARI project, which involved theoretical formulating, models and experimental measures. Among air pollution monitoring activities, an intensive aircraft field campaign was carried out in May 2008, in order to analyse meteorological conditions and particulate pollution evolution over Europe. This study had several objectives:

Mapping tropospheric aerosols in Europe.Detecting and analysing differences in aerosol properties in several air masses, as well as describing transitions in these properties in boundary regions (e.g. transitions from rural and industrial regions).Studying changes in aerosols during long-term transportation phenomena.Linking the obtained measures to ground based data from some EUSAAR super-sites: Melpitz and Hohenpeißenberg (Germany); Cabauw (Netherlands); Mace Head (Ireland); Hyytiälä (Finland); and Vavihill (Sweden). This was intended as a way to verify that ground measurements could accurately describe vertical pollutant composition profiles.

Two aircrafts were used along the survey study. One flied in the lower free troposphere (and even the boundary layer), and another airplane flied up to the point where air stops cooling with height (tropopause level). In order to elucidate aerosol size distributions differential (DMPS) or Scanning Mobility Particle Spectrometer (SMPS) techniques were used at ground stations and Passive Cavity Aerosol Spectrometer Probes (PCASP) were used in aircrafts. Additionally, a condensation particle size analyser was used for quantifying condensation nuclei (particles around which cloud droplets coalesce). Along with these measures, data from the European Centre for Medium-Range Weather Forecasts were used for modelling meteorological patterns.

When air measures were compared with ground measurements, good correlation demonstrated that air volumes measured at ground stations were the same than those measured from aircrafts. During the first weeks of May, an anticyclone centred over North Sea and Denmark dominated European meteorology, leaving clear skies. This anticyclonic blocking event, which leads to an accumulation of pollutants, has been often found in the European Atlantic Region. In the second half of May, pollution stayed in continental Europe, and some flow regime changes led to two cyclones in northern Italy and Scandinavia. The northern Italy cyclone sent warm and moist air masses towards Central and Eastern Europe, whereas the Scandinavian cyclone threw cold air to Central Europe. The conjunction of these air masses caused cloudiness and rain in the Alps region, the Czech Republic, Southern Poland, Belarus and Russia.

These climatic events affected the aerosol levels found in both air and ground measurements. So, inner recirculation during anticyclone blocking was demonstrated by high pollution levels in Vavihill and Melpitz stations. Moreover, higher black carbon (wastes from incomplete combustion) levels were found in Cabauw station (0.70 μgm−3), probably due to pollutant uptake of anthropogenic emissions from Germany. Melpitz and Cabauw ground stations showed a typical diurnal cycle (with maximums in the morning and minimums in the afternoon), where pollution is vertically mixed during daytime and keeps stationary in the night. High black carbon concentrations were also found in Irish ground station (Mace Head), because of an advection of highly polluted air masses. Around 20% of the air masses getting at Mace Head were originated in the continent.

Cloud nuclei number concentrations showed large discrepancies between ground (Hohenpeißenberg station) and airborne measures in South Germany (3600 cm−3 and 8200 cm−3) during the anticyclone period.
This was attributed to fresh air transport in the high parts of boundary level, whereas ground measures reflected aerosol levels from Munich

In the second observed climatic period, black carbon emissions were found to be transported eastward. Additionally, precipitations reduced the pollutions levels. Cloud nuclei number vertical distribution, on its part, showed an almost continuous negative vertical gradient to the top of the boundary layer.

T. Hamburger, G. McMeeking, A. Minikin, W. Birmili, M. Dall’Osto, C. O’Dowd, H. Flentje, B. Henzing,
H. Junninen, A. Kristensson, G. de Leeuw, A. Stohl, J. F. Burkhart, H. Coe, R. Krejci, and A. Petzold. Overview of the synoptic and pollution situation over Europe during the EUCAARI-LONGREX field campaign. Atmos. Chem. Phys., 11, 1065–1082, 2011.