To generate benzene samples with known concentrations, cylinder gas containing 1 ppm of benzene in nitrogen balance was diluted with compressed air. The compressed air was first sent through an active carbon column filter to ensure it is free of benzene. The mixing ratio was controlled with mass flow controllers. A flow of 1 L min -1 of the benzene mixture was flowing pass the sample input of the measurement setup and the flow was sampled by the instrument in bypass mode. Figure shows the response of the measurement system to varying benzene concentrations. Each point corresponds to one 90 s cycle. The benzene concentration in the sample flow was kept constant for a duration of 30 min and then changed to a new level. Between each 30 min constant concentration measurement set, a blank measurement with no benzene was performed from a separate gas flow containing only the filtered compressed air. This allowed us to verify that the zero level was retained over the measurement set. During the blank measurement, the benzene concentration in the mixed flow had time to stabilize to the new level. This process was repeated several times over a 4.5 h measurement set.