A waste gas is contacted with a mercury removal agent to remove mercury and a flue gas conditioning agent to alter a resistivity and/or cohesivity of particulates. The flue gas conditioning agent can be substantially free of SO3and/or comprise more than about 25 wt. % SO3, and/or the mercury removal agent can be substantially unaffected by the flue gas conditioning agent. An amount of mercury removed from the waste gas in the presence of the flue gas conditioning agent can be the same or more than that removed from the waste gas in the absence of the flue gas conditioning agent. An amount of the acid gas removed, by an acid gas removal agent, from the waste gas in the presence of the flue gas conditioning agent can be the same or more than that removed from the waste gas in the absence of the flue gas conditioning agent.