His research fields include transport, deposition and air/sea-gas exchange of atmospheric trace constituents, such as mercury and persistent organic pollutants (POPs) with special emphasis on substances of emerging concern for the coastal, marine, and polar environment. Ralf is editor of the EGU Open Access Journal "Atmospheric Chemistry and Physics" and associate editor of "Chemosphere". He has published more than 220 articles in peer reviewed journals and several book chapters (h-Index = 61) and has co-edited three books.