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air quality; atmospheric aerosols; bromine; central Europe; lead; seasonality; vehicular traffic emissions
Abstract:
Intention, Goal, Scope, Background. Abatement measures since the 1970s have depleted lead and bromine levels in the atmosphere over large parts of Europe. Our knowledge of the atmospheric cycling of these elements while a several decade- long period of intensive mobilization reaches its end is incomplete. Objective. We have characterized the trends in the atmospheric levels of Pb and Br and present-day temporal and spatial variabilities. Methods. This was achieved by short-term (weeks) and long-term (years) measurements of particulate Pb and Br at various sites in Germany. Samples of atmospheric particulate matter were collected on filter membranes and analyzed by x-ray fluorescence. Results and Discussion. Average Pb levels at rural and urban inland sites did not exceed concentrations in background aerosols, sampled at a Baltic Sea coastal site, by more than a factor of 3. Due to sea salt, bromide inland particulate Br levels are below those at a coastal site. There, non-sea salt Br, however, is significant as well. Urban Pb and Br levels are not necessarily higher than rural levels. The concentration levels have decreased in such a way that the previously common source, local vehicular traffic emissions, is no longer predominant. Regional rather than local sources have been increasingly determining the concentrations since the 1990s. This is more pronounced for Br than for Pb. We found indications for coal burning and long-range transport as significant Pb sources. For particulate Pb species, a range of ages (elapsed time since Pb emission) has been found. This range shows two maxima corresponding to characteristic times of 72 and 24 h. Conclusions. The (mean) atmospheric residence time of particulate Pb is longer than the residence time of Br, in particular in the wintertime. The chemical species contributing to atmospheric Pb should be addressed in future studies. Recommendation and Outlook. Clearly, despite effective abatement measures, atmospheric Pb will continue to be dominated by anthropogenic mobilization. The influence from long-range transport can be expected to decrease with the effectiveness of abatement programmes in neighbouring countries of the region.
