Southern California’s smog-fighting agency is cracking down on paint makers, requiring them to spend hundreds of millions of dollars to help clean the region’s air. The South Coast Air Quality Management District on Friday adopted tough new rules that will force manufacturers to make expensive reformulations to nearly half the industrial and household paints and primers sold in the region, substantially cutting volatile organic compounds, which contribute to the formation of smog. The shift is expected to raise the prices of affected paints by a third. Some manufacturers argue that it will be impossible to produce certain paint products under the new rules, and that small paint companies will be driven out of business.