Heavy metals in precipitation

The data of annual mean concentrations in precipitation are weighted using the weekly concentrations and precipitation amounts to derive so called volume weighted concentrations (ng-μg/L). The volume weighted annual mean concentrations in precipitation for 2019 are presented in Table 23. The wet depositions are obtained by multiplying the volume weighted concentrations with the precipitation amounts (ng-mg/m²) and the results for 2019 are presented in Table 24. Calculated volume weighted monthly mean concentrations and wet depositions for all the elements are shown in Annex A.2.1-A.2.33.

The results show that the highest annual mean concentrations of all heavy metals, are observed at Svanvik and Karpdalen due to high emissions from the smelters in Nikel (Russia) close to the Norwegian border. Significantly higher levels of the heavy metals are observed when there is easterly wind from Russia and the Kola Peninsula. The influence from the Russian smelters on the eastern Finnmark environment has been repeatedly demonstrated through the national moss surveys (Steinnes et al.

2016). Further details and discussion of the data from Svanvik and Karpdalen can be found in the annual report for the programme “Russian-Norwegian ambient air monitoring in the border areas”

(Berglen et al., 2019).

The levels and deposition of lead, cadmium and zinc observed are highest at Birkenes followed by Hurdal and Kårvatn reflecting the decreasing distances to the main emission sources in continental Europe (EMEP, 2019).

Table 163: Annual average volume weighted mean concentrations of heavy metals (µg/l) and mercury (ng/L) in precipitation in 2019.

Pb Cd Zn Ni As Cu Co Cr Mn V Al Hg

Figure 39: Volume weighted monthly mean concentrations of lead, cadmium and mercury in precipitation in 2019.

The monthly mean concentration for lead, cadmium and mercury are shown in Figure 39. There is no clear visual seasonal variation, but elevated levels for most components and sites are seen in April, and of cadmium at Hurdal in July. The spring peaks are also seen for heavy metals in aerosols and likely connected to episodes with long range transport of air pollution from the European continent. In 2019, there was an unusual large-scale event during April, which caused high concentrations of many pollutants at several of the mainland sites. April 2019 was the second warmest and second driest April in Norway since 1900 caused by a persistent high-pressure system in Europe with warm and dry air for

a long period. The episode carried pollution from extensive fires in Eastern Europe, as well as dust from probably Sahara, and pollution from traffic and industry in continental Europe.This event is described in more details in the report on long-range transported air pollutants in Norway (Aas et al., 2020).

Figure 40: Time series of volume weighted annual mean concentrations of lead, cadmium and mercury in precipitation at Norwegian background stations.

Figure 40 and Table A.2.26 show volume weighted annual mean concentrations in precipitation from 1979 to 2019. In 2019, the concentrations were in general somewhat lower than in 2018 at Birkenes an somewhat higher at Hurdal and Kårvatn.

For the statistical trend analysis, the non-parametric “Mann-Kendall Test” has been used on annual means for detecting and estimating trends (Gilbert, 1987). The Mann-Kendall test has become a

standard method when missing values occurs and when data are not normally distributed. In parallel to this, the Sen’s slope estimator has been used to quantify the magnitude of the trends.

In a long term perspective, the concentrations of lead in precipitation at Birkenes and Kårvatn, (and Hurdal since 1990) have been largely reduced; almost 100% between 1980 and 2019; 38-98% since 1990, and 58-61% since 2000 (except at Hurdal with no significant trend since 2000) (Table 23). Also for cadmium in precipitation, there are substantial reductions: 95-99% between 1980 and 2019;

50-76% since 1990, and 54-68 % since 2000. except at Hurdal with no significant trend since 2000) When combining the datasets from Lista and Birkenes, mercury levels appear to have been significantly reduced (64%) since 1990. However, this reduction might be influenced by different precipitation amounts and deposition rates at the two sites. For example, when comparing the precipitation amount at the two sites, slightly lower amounts are seen at Lista than at Birkenes. The results from a trend analysis that combines the datasets is therefore somewhat uncertain, though there is no apparent change in the concentration or deposition timeseries when sampling collection was relocated. On the other hand, it is believed that Lista and Birkenes are influenced by similar air masses as the two observatories are situated at the south coast of Norway. There is also a decrease in mercury concentration at Birkenes from 2004 to 2019 with 44%. While the concentration of mercury in precipitation have decreased in a long term perspective, the precipitation depth have increased in the same time period. (Figure 41 and Table 2). Wet deposition is a combination of the two and has decreased at the same pace as concentration.

Figure 41. Time series of volume weighted annual mean concentration of mercury and the precipitation amount (bottom), and the wet deposition (top) at Lista (1989-2003) and Birkenes (2004-2019).

The concentrations of zinc in precipitation have been reduced by 68% since 1980 and 42% since 1990 at Birkenes. In contrast, a significant increase of zinc has been observed in precipitation at Kårvatn during the last periods (Table 23). There One should notice that the concentration level at Kårvatn is relativly low and that it is in general quite large annual variations in zinc, with increases at some sites for some years. This may be due to possible contamination of zinc during sampling or influence of local sources, e.g. from resuspention of contaminated dust, thus the choice of time period for the trend analysis may influence whether one detect trends or not.

The reductions in lead and cadmium are consistent with those observed at other EMEP sites with long-term measurements and can be explained by large European emission reductions of these elements (Tørseth et al., 2012; Colette et al., 2016).

At Svanvik there has been a reduction in lead and arsenic from 1990 and 2000 while no significant reduction trends for cadmium and the other trace elements, except of zinc from 2000. There are large annual variations in the concentration levels at this site, and this may be due to meteorological variations as well as changes in the composition of the ore used at the smelters in the Kola Peninsula.

For further discussion, it is referred to the report by Berglen et al. (2019).