five-minute period was excluded from computation of the average
for the measurement period.
Experience indicated that leakage in the ion conductivity
chambers could occur during periods of rain or high humidity.
Periods with zero-voltage chamber current in excess of 25 pA
were excluded from the ion data. Periods within 15 minutes
of a bucket tip of the rain gauge and periods of rain identified
by local weather watchers were also excluded from the analysis
of ion concentration.