Katriina Kyllönen

Trace element deposition and trends during a ten year period in Finland.

The deposition of aluminium, arsenic, cadmium, chromium, copper, iron, lead, manganese, nickel, vanadium and zinc in bulk precipitation was examined at eight background stations in Finland during the last 10 years (1998-2007). The annual deposition was from the lowest values to the highest Cd<As<Cr<Ni<V<Cu and Pb<Mn<Zn<Al<Fe. Most of the elements had a south to north decreasing gradient mainly due to minor domestic emissions in the north, growing distance to the large European source areas and differences in the length of snow-cover period. Element enrichment factors divided the trace elements to the following categories: (1) slightly enriched Cr, Fe and Mn; (2) moderately enriched Cu, Ni and V; and (3) highly enriched As, Cd, Pb and Zn. Trend analysis of annual depositions showed that the established decreasing trend in As and Pb deposition continued during our study period while Cr, Cu and Fe depositions have lately increased. No statistically significant trends were detected for Cd, Mn, Ni, V and Zn during the studied years. Additionally, the measurement uncertainty of trace elements was evaluated for the whole measurement chain.

A vegetation control on seasonal variations in global atmospheric mercury concentrations

Anthropogenic mercury emissions are transported through the atmosphere as gaseous elemental mercury (Hg(0)) before they are deposited to Earth’s surface. Strong seasonality in atmospheric Hg(0) concentrations in the Northern Hemisphere has been explained by two factors: anthropogenic Hg(0) emissions are thought to peak in winter due to higher energy consumption, and atmospheric oxidation rates of Hg(0) are faster in summer. Oxidation-driven Hg(0) seasonality should be equally pronounced in the Southern Hemisphere, which is inconsistent with observations of constant year-round Hg(0) levels. Here, we assess the role of Hg(0) uptake by vegetation as an alternative mechanism for driving Hg(0) seasonality. We find that at terrestrial sites in the Northern Hemisphere, Hg(0) co-varies with CO2, which is known to exhibit a minimum in summer when CO2 is assimilated by vegetation. The amplitude of seasonal oscillations in the atmospheric Hg(0) concentration increases with latitude and is larger at inland terrestrial sites than coastal sites. Using satellite data, we find that the photosynthetic activity of vegetation correlates with Hg(0) levels at individual sites and across continents. We suggest that terrestrial vegetation acts as a global Hg(0) pump, which can contribute to seasonal variations of atmospheric Hg(0), and that decreasing Hg(0) levels in the Northern Hemisphere over the past 20 years can be partly attributed to increased terrestrial net primary production.Terrestrial vegetation contributes to the seasonal variation of atmospheric mercury concentrations, according to analyses of atmospheric trace gas dynamics and satellite data. The data show that the photosynthetic activity of vegetation correlates with atmospheric mercury.