Manganese in the urban atmosphere: identifying anomalous concentrations and sources

Abstract

Industrial emissions can raise urban background levels of inhalable Mn particles in an order of magnitude above normal, eclipsing the contribution made by natural sources and traffic. The source of such emissions can be identified using a multidisciplinary approach which integrates ICP-MS chemical analyses of PM(10) and PM(2.5) samples with positive matrix factorization source apportionment modelling, scanning electron microscopy and meteorological data. We apply this methodology to data from Santander (N Spain), where morning Mn-bearing industrial contamination sourcing from the SW is returned towards the city by afternoon NE sea breezes. This wind direction reversal carries the industrial pollution plume inland, detectably raising urban background levels of MnPM(10) in the town of Torrelavega 20 km away. Industrially sourced daily urban background Mn levels at Santander reach >1,000 ng/m(3), average >150 ng/m(3). We demonstrate the anomalous nature of such concentrations by comparing them with >2,500 PM(10) chemical analyses of ambient PM(10) from other sites in Spain which show how current background Mn levels in urban air typically average only 10 ng/m(3), rising to 20-25 ng/m(3) in city traffic sites. Daily levels of atmospheric Mn PM(10) only rarely exceed 50 ng/m(3), usually during desert dust intrusions which, in extreme cases (such as Canary Islands "calima" events from Africa) can produce Mn concentrations of 100-125 ng/m(3).