Abstract
Abstract. In July 2013 very strong boreal fire plumes were observed at the northern rim of the Alps by lidar and ceilometer measurements of aerosol, ozone and water vapour for about 3 weeks. In addition, some of the lower-tropospheric components of these layers were analysed at the Global Atmosphere Watch laboratory at the Schneefernerhaus high-altitude research station (2650 m a.s.l., located a few hundred metres south-west of the Zugspitze summit). The high amount of particles confirms our hypothesis that fires in the Arctic regions of North America lead to much stronger signatures in the central European atmosphere than the multitude of fires in the USA. This has been ascribed to the prevailing anticyclonic advection pattern during favourable periods and subsidence, in contrast to warm-conveyor-belt export, rainout and dilution frequently found for lower latitudes. A high number of the pronounced aerosol structures were positively correlated with elevated ozone. Chemical ozone formation in boreal fire plumes is known to be rather limited. Indeed, these air masses could be attributed to stratospheric air intrusions descending from remote high-latitude regions, obviously picking up the aerosol on their way across Canada. In one case, subsidence from the stratosphere over Siberia over as many as 15–20 days without increase in humidity was observed although a significant amount of Canadian smoke was trapped. These coherent air streams lead to rather straight and rapid transport of the particles to Europe.
Highlights
The increase of tropospheric ozone during the past decades has been frequently attributed to a growth in anthropogenic air pollution
The North American fire plumes were observed in southern Bavaria from 1 to 23 July 2013, enclosed by two periods of Saharan-dust advection
Due to the low cloud coverage, backscatter data from Leutkirch are used to illustrate the presence of fire aerosol layers in the free troposphere above southern Germany (Fig. 3)
Summary
The increase of tropospheric ozone during the past decades has been frequently attributed to a growth in anthropogenic air pollution. This development has recently continued only in rapidly developing regions such as in eastern Asia. Measurements at high-altitude stations in Europe such as Jungfraujoch (Switzerland, 3500 m a.s.l.) and Zugspitze (Germany, 2962 m a.s.l.) have shown growing ozone concentrations even more than a decade after the onset of diminishing anthropogenic ozone precursor concentrations (e.g., Cui et al, 2011; Oltmans et al, 2012). Scheel (2005) found that the role of STT for the Zugspitze site has been grossly underestimated, with an estimated average STT fraction of about 40 % reached by 2004 Another strong source of STT previously underestimated was emphasized by Sprenger
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