Sampling Errors in Flux Measurements of Slowly Depositing Pollutants

Abstract

Sampling errors in vertical flux measurements obtained by eddy correlation methods are investigated by specifying a jointly normal?lognormal density distribution for the vertical velocity and scalar concentration. The probability density function for the sample velocity-concentration correlation coefficient is then determined. It is found that sampling errors in this coefficient may be excessively large for low concentration scalars when the deposition velocity is of order 0.1 cm s?1, the time constant of the scalar sensor is of order 1 sec and measurement time of order 1 h. The technique can be applied to any joint distribution for vertical velocity and scalar concentration such that these variables have a joint distribution which can be transformed into the jointly normal.