The paper discusses the in-flight capture of elemental mercury (Hgo) by a chlorine (CI)-impregnated activated carbon. Efforts to develop sorbents for the carbons using dilute solutions of hydrogen chloride (HCI) leads to substantial increases in Hg capture. HCI treatment at ambient temperature of a commonly used, commercially available activated carbon-DARCO FGD, NORIT Americas, Inc.-has previously been shown to result in significant improvement in the fixed-bed capture of Hgo and mercuric chloride (HgC12). In the study presented here, the C1-impregnation process was optimized for Hg capture based on comparative testing in a bench-scale, fixed-bed Hgo absorption system. The optimized sorbent was then produced on a larger scale (5 lb per batch) and tested for in-flight, short-time-scale capture of Hgo in a flow reactor. The sorbent was entrained in Hgo-laden flue gases of varied compositions with gas/solid contact times of about 3-4 s. C1-impregnated FGD exhibited significant Hgo removal (80-90%), compared to virgin FGD (10-15%), across the whole range of very low carbon-to-mercury weight ratios (1000-1 to 5000-1). Preliminary cost estimates indicated that approximately 53% reduction of the total annual cost of Hg control could be possible when using C1-impregnated FGD.