Smoke, Fog, and Why Your Measurements Are Off

Here's something to ask the companies that manufacture your hazards detection equipment- what is the effect of smoke or fog on their measurements?
Let me give you an example.
Let's say you're depending on a RAE Systems PID to measure your surroundings for VOC's such as benzenes on a foggy day.  How much does the fog affect your reading if at all?  Humidity and PID readings don't mix well, although Ion Science, Inc. seems to have a PID technology that is less affected by humidity.
Or here's my favorite:  we were involved in putting out a chemical fire some months ago and there was the possibility of hexane exposure. 
Of course, we pulled out the PID, this time one from Industrial Scientific.  But there was smoke in the air.  How much did the smoke affect our readings?
Ever wonder how much of an affect humidity has on long distance (say 300 feet) temperature measurement with an IR gun?  Say you're trying to keep your distance from a rail car that might be suspect.  If the humidity is 90%, will it affect your reading?
Next posting we'll see what the manufacturers say about it, then after that will do a reality check.