Montgomery County on Thursday approved a carbon dioxide tax, becoming the first East Coast municipality to levy a tax on emitters.

The tax will affect just one business in Maryland’s largest county — the Mirant Corp.’s Dickerson coal-fired power plant.

The $5 per ton tax will raise an estimated $10 million to $15 million a year on the three million tons of carbon the power plant emits annually, county officials said. Pepco Holdings Inc., a power provider that buys electricity from Mirant for Maryland and District of Columbia customers, told county officials the tax will not result in higher electricity rates for customers.

Environmentalist groups praised the Montgomery vote. They noted that counties in the San Francisco Bay Area and Boulder, Colo., also levy carbon taxes.

Montgomery County in April sold $23 million of certificates of participation to Morgan Stanley at a true interest cost of 2.37%.

The county is rated triple-A by Moody’s Investors Service, Standard & Poor’s and Fitch Ratings. The COPs are rated double-A plus by all three ­agencies.

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