Reactive gaseous mercury in the marine boundary layer: modelling and experimental evidence of its formation in the Mediterranean region

Reactive gaseous mercury (RGM) concentrations have been modelled using a photochemical box model of the marine boundary layer (MBL) and compared to measured data obtained during a research cruise. The model has been constrained by using measured concentrations of elemental Hg and ozone, as well as measured temperature and relative humidity. The results show good qualitative agreement both during the rough weather encountered on the first part of the voyage and the second, calmer period of the campaign. Quantitative agreement is obtained using a box height of 100 m during the first leg of the campaign. The modelled and measured results from the second leg agree as far as the nocturnal RGM concentration minima are concerned but underestimate the daytime maxima by a factor of two. The comparison of the modelled with measured results supports the hypothesis that there are daytime mercury oxidation reactions occurring which have not yet been identified.