Abstract: An air sampling and analysis system has a plurality of air sampling tubes extending between an analytical laboratory and a number of remote locations where samples are taken. Means are provided for continually drawing air through the sampling tubes during times when they are not connected to a analytical instrument for measuring concentration of various gases. Means are also provided adjacent to the inlet of at least some of the sampling tubes for converting a vapor which may not travel the full length of the sampling tube, to a gas which will travel the full length of the tube. The concentration of the vapor can be found by measuring the composition of the air sample with conversion and subtracting a similar composition without conversion. Examples of vapors that are converted include hydrogen sulfide and ammonia.