Boral Roofing’s Smog-Eating roof tile line includes titanium dioxide, a chemical that clears the air of nitrogen oxide pollution. A catalyst in the concrete tiles reacts with sunlight to reduce pollution, kill algae, and repel dirt. About 2,000 square feet of the tile breaks down the same amount of smog a car produces driving 10,800 miles, says the manufacturer. Boral Roofing. 800.571.8453.