Is secondhand smoke a pollutant?

Not if you ask the tobacco companies, but it is now in California, following a state agency's ruling on the matter:

California became the first state to declare secondhand smoke a toxic air pollutant Thursday, putting tobacco fumes in the same category as diesel exhaust, arsenic and benzene because of its link to breast cancer.

The unanimous decision by the state Air Resources Board relied on a September report that found a sharply increased risk of breast cancer in young women exposed to secondhand smoke. It also links drifting smoke to premature births, asthma and heart disease, as well as other cancers and numerous health problems in children.

This is a huge step forward in the fight against tobacco. If secondhand smoke is considered poisonous (which it clearly is,) the public must be protected from it. This might in turn mean even fewer places or open spaces for smokers to freely light up, which in turn will translate into fewer people taking on the habit, given it's lack of social acceptance and difficulty to practice it.