Emissions are deadly waves of radiation that sweep across the wasteland at random times. in the game STALKER Clear Sky. the protagonist encounters this phenomenon at the beginning of the game. after he wakes up from his radiation induced coma. Professor Beanpolev explains that this has effected his nervous system, but has increased his motor skills, unlike his Clear Sky comrades who where killed during the immolating blast. im going to post a youtube video of an emission.
I hope this helps.