A decadal shift in total gaseous mercury concentration levels in Seoul, Korea: changes between the late 1980s and the late 1990s

The concentrations of total gaseous mercury (Hg) were determined from an urban area between two different time periods of the late 1980s and the late 1990s and compared to evaluate the mechanisms regulating Hg distribution over a decadal period. Because of time gap and the associated changes in source/sink relationships, the observed concentration levels of Hg were remarkably different between the two periods. The results showed that the Hg levels in the former period were averaged to be 14.4 +/- 9.56 ng m(-3) (N = 2714), while the latter period was recorded at approximately threefold reduced values of 5.34 +/- 3.92 ng m(-3) (N = 2576). Using the measurement data for the two independent periods, we were able to describe the basic features of Hg distribution that correspond to each time period. When inspected over a 24h scale, two contrasting patterns emerged for the two time periods. The former was characterized by enhanced concentration levels during daytime, but the latter with relative depletion during daytime. The results of the two periods, when inspected over seasonal scale, showed many similarities and dissimilarities simultaneously. In order to analyze the factors affecting Hg distributions of each period, we conducted correlation analysis on the data groups divided both diurnally and seasonally. Results of these analyses consistently indicate that correlation patterns may be associated with the factors regulating the diurnal variability of Hg. The data for the late 1980s consistently indicate the presence of a single dominant source process that can be represented by the use of coal. However, the patterns described for those of the late 1990s suggest that the sources of Hg be tightly tied up with the general sources of air pollution that can lead to the degradation of urban air quality. In addition, we suspect that notable shifts in meteorological conditions between the two periods might also have been conducive to changes in Hg concentration levels to a certain extent. (C) 2002 Elsevier Science Ltd. All rights reserved.