Recent ATESR Lab results suggested that aside from being generally more difficult to collect in an ESP, collection of powdered activated carbon (PAC) also is substantially different than fly ash.  The analysis uses historical power generation and coal usage data for the U.S. and assumes that, 1) fine PAC exhibits size and optical characteristics similar to black carbon (BC, aka soot), and 2) the much lower resistivity of PAC as compared to fly ash can be parameterized in terms of in a collection efficiency differential.  The resulting estimates (shown below) present black carbon (BC) emissions increases from coal-fired power plants during PAC injection as a function of PAC injection rate and the differential ESP collection efficiency between PAC and fly ash.  The baseline BC content of fine fly ash emitted from ESPs is not well characterized and is the source of significant variability in the estimated BC emissions increases:  assuming high BC content on emitted fine fly ash from ESPs results in lower estimated increases during PAC injection, with the reverse being true for assumed low BC content in emitted fine fly ash.  In the case of low BC content of the emitted fine fly ash (top figure, below), projected increases in BC emissions are measured in terms of multiples:  the lowest PAC injection rate resulted in > 300% increase in BC emissions even when applying the overly optimistic assumption of no collection efficiency differential between PAC and fly ash.  In the case of high BC content of the emitted fine fly ash, increases ranged from 5 to 73%.  Projections were also developed for both bromine-impregnated and finely ground sorbents.