Practical experience acquired on operation of large scale flue gas scrubbers often fails to agree with the theoretical knowledge on which the design and operation of flue gas scrubbers are based. The absorption of SO2, HCl, and mercury reveal the additional effects to be considered for optimal design and operation of flue gas scrubbers. Mist formation, wetting of plastic packing, or the buffer effect on the absorption of concentration peaks are such additional effects. The influence of these effects on the design and operation of flue gas scrubbers is analyzed by the calculation of typical examples.