Although many studies have evaluated the performance of activated carbon, most of them were performed at high VOC (Volatile Organic Compound) concentration levels (~ppmv). The performance of the sorbent media at realistic concentration (ppbv) is still not clear due to lack of experimental data. The objective of this study is to investigate the adsorption mechanism of activated carbon at different concentration levels and correlate the removal capacity as represented by the partition coefficient (Kma), with the challenge concentration (C) of VOCs. A series of tests were conducted at six concentration levels of Toluene from 107 ppm to 66 ppb, and different test conditions (particle size, flow rate and sorbent bed length). It was found that the partition coefficient varied with the concentration in the form of Kma=aCb or log(Kma)=A+BlogC. The correlation is essential to accurate representation of the media bed's breakthrough curve, and to predicting the performance of sorbent media at low concentration based on the data obtained from standard high concentration tests of sorbent media.