This paper illustrates inhomogeneities in pollutant time-series data caused
by changes in data reporting practices. These inhomogeneities may have a s
ubstantial effect on trend assessments. Therefore, in estimating trends or
mean levels in pollutant time series or attributing changes in pollutant le
vels to an emission control policy, it is important to homogenize time-seri
es data. (C) 2000 Elsevier Science Ltd. All rights reserved.