The influence of contrasting ambient SO2 concentrations in the Czech Republic in 1995 and in 2010 on the characteristics of spruce bark, used as an air quality indicator

Spruce bark specimens (n = 1179) were collected in 1995, when the air in the Czech Republic was already recovering from being dominantly polluted by SO2, and again in 2010 (n = 1530), when the ambient SO2 concentrations had decreased sixfold and had reached levels of concentrations comparable with the other airborne pollutants. The territorial relative bark parameter value distributions showed similar patterns in 1995 and 2010. The highest values for H+ and SO42− concentrations and electrical conductivity were found in the brown coal basin in the NW part of the Czech Republic, and in nearby sites where brown coal was burned in industrial operations. A significant decrease in the bark parameter values was detected between 1995 and 2010. The recovery of the bark characteristics was about two times slower than the reduction in territorial SO2 emission amounts. No significant differences in the rate at which the bark parameters diminished were found between industrial and rural areas. The bark parameters correlated negatively with the elevation, and significant correlations among the bark parameters were found in 1995 and 2010. In 2010, the slope of the regression lines for the relation of bark parameter values was about twice higher than in 1995, and the correlation coefficients increased. Recently, the soluble SO4 concentrations in bark have comprised about one third of the total bark sulphur content in the investigated territory.