Abstract
Replicated measurements of a pollutant regularly repeated over a year are often designed, each of which gives several daily average concentrations. The average of all the measured daily average is an estimate of annual average, but it varies depending on the days the measurements are carried out. The quality of estimated averages, relative to the real annual average has been examined using NO2 concentrations during 1996 from Tokyo and during 1994-1996 from Aichi areas.
The relative error, defined by the ratio of the standard deviation of the estimated averages to the real annual average, is generally reduced with increased times of measurement, and with number of days in each measurement. However, if the number of days in every measurement is confined to three or four, the relative error in case of three time measurements, in other words, measurements carried out every four months, is often smaller than that in case of four time measurements.
The above results were influenced by periodical variations in meteorology during the examined years, and are not necessarily valid when meteorological conditions vary from year to year.
