This paper considers how moderate actions to slow atmospheric accumulation of greenhouse gases from fossil fuel use also could reduce conventional air pollutants in the United States. The benefits that result would be "ancillary" to greenhouse gas abatement. Moreover, the benefits would tend to accrue locally and in the near term, while benefits from reduced climate change mostly accrue globally and over a time frame of several decades or longer. The previous literature suggests that changes in nitrogen oxides (NOx) would be the most important consequence of moderate carbon policies. We calculate these changes in a detailed electricity model linked to an integrated assessment framework to value changes in human health. A tax of $25 per metric ton of carbon emissions would yield NOx related health benefits of about $8 per metric ton of carbon reduced in the year 2010 (1997 dollars). Additional savings accrue from reduced investment in NOx and SO2 abatement in order to comply with emission caps. These savings sum to $4-$7 per ton of carbon reduced. Total ancillary benefits of a $25 carbon tax are estimated to be $12-$14, which appear to justify the costs of a $25 tax, although marginal benefits are less than marginal costs. At a tax of $75 per ton carbon, greater health benefits and abatement cost savings are achieved but the value of ancillary benefits per ton of carbon reductions remains roughly constant at about $12.