Using a well known method for laboratory plasma diagnostic , the Boltzmann-plot , we discuss the physical properties in Broad Line Region ( BLR ) of Active Galactic Nuclei ( AGN ) .
We apply the Boltzmann-plot method to Balmer lines on a sample of 14 AGN , finding that it may indicate the existence of ” Case B ” recombination or Partial Local Thermodynamical Equilibrium ( PLTE ) .
For BLR of AGN , where PLTE exists , we estimated the electron temperature and density of BLR .
The estimated electron temperature ( T \sim 13000 - 37000 K ) are in good agreement with previous estimates .
The estimated electron densities depend on opacity of the emitting plasma in BLR .
They are from N _ { e } \sim 10 ^ { 9 } cm ^ { -3 } for optically thick to N _ { e } \sim 10 ^ { 14 } cm ^ { -3 } for optically thin emission plasma in BLR .
The estimated electron temperature has been shown to be velocity dependent , and it decreases for higher velocities .
Although the alternative explanation than PLTE indicated by Boltzmann-plot may be considered ( e.g .
high intrinsic reddening ) , the method may give the quick estimate of physical conditions in BLR before to apply the sophisticated methods .