It is very important to measure particle size distributions in flue ga
s. In conventional methods, it is necessary to use a complicated class
ifier like the Andersen Stack Sampler or particle size measuring instr
uments after an isokinetic sampling in order to get the particle size
distribution. On the other hand, the new measurement method utilizes s
ampling error due to the anisokinetic sampling as a classification met
hod. When the sampling velocity is not equal to the main flow velocity
, the ratio of the main flow velocity to the sampling velocity has a l
inear relation with the measured concentration and also the ratio of t
he measured concentration to the actual concentration. As the slope of
this line is determined by the particle size distribution, it is poss
ible to estimate the particle size distribution. This method has been
experimentally proven for several kinds of particles from 0.5 to 40 mu
m in median diameter, and the results are in good agreement with size
distributions measured by conventional methods.