Simultaneous measurements of total gaseous mercury at four sites on a 800 km transect: spatial distribution and short-time variability of total gaseous mercury over central Europe

Over a distance of approximately 800 km simultaneous measurements of total gaseous mercury (TGM) were performed at four sampling sites between Stockho lm and Berlin. The time resolution of mercury concentration measurements wa s 5 min. During the sampling period from 26 June to 7 July 1995, event samp ling for precipitation was carried out using bulk samplers. In addition to the mercury data, the most common meteorological and air-quality parameters were determined. Comparing the TGM background concentrations at the four s ites, a weak but statistically significant south-to-north declining TGM gra dient was found. From the most southern sampling site to the northern most site median values of 1.93, 1.78, 1.53 and 1.54 ng m(-3) TGM were detected. Compared with the median TGM concentration observed at the two Swedish sit es, the regional background concentration near Berlin was elevated by about 25%. Whereas the 0.5 h average TGM concentration varies at the Swedish sam pling sites in a very narrow range of only 0.69 ng m(-3), a much broader ra nge of 3.28 ng m(-3) was observed at the southern sites. The increased TGM variability near Berlin was characterised by a diurnal cycle with a distinc t maximum in the early morning hours (about 4:00 a.m.) before sun rise. The short time variability of the TGM concentration measured at the four sites on the south-to-north transect shows regional differences. A decreasing va riability from the most southern to the most northern site became evident. (C) 1999 Elsevier Science Ltd. All rights reserved.