CHATTANOOGA, Tenn. (AP) — Volkswagen officials underestimated emissions from the paint shop at the company's auto assembly plant in Chattanooga.

According to the Chattanooga Times Free Press ( ), the carmaker has asked the Chattanooga-Hamilton County Air Pollution Control Bureau for a variance.

Bob Colby, who heads the agency, said the company had to calculate what it thought nitrogen oxides emissions would be as the plant was being built in 2008.

When production began, it became obvious the emissions exceeded the amount the company had predicted.

"The end result ... is they were off by 20 percent," Colby said.

The oxides can be a component in acid rain and, as nitrogen dioxide, can combine with volatile organic compounds and be acted upon by sunlight to form ozone or smog.

According to the National Institutes of Health, breathing nitrogen oxide can irritate the eyes and nose and cause respiratory problems such as a fluid buildup in the lungs.

The VW plant in Chattanooga last year became the only auto plant in the world to receive certification as Platinum Leadership in Energy and Environmental Design by the U.S. Green Building Council.

LEED certification looks at factors including sustainable sites, water efficiency, energy and atmosphere, materials and resources, indoor environmental quality and innovation in operations.

Volkswagen spokesman Guenther Scherelis in Chattanooga said that, in 2008, pollution equipment hadn't yet been specified for the plant but estimates had to be given for the permitting process.

Scherelis said the higher emission level would still be 77 percent lower than the industry standard for comparable paint shops.

Documents the company filed with the air pollution bureau in support of its request indicated auto production at the plant could double to more than 300,000 vehicles a year.

Scherelis noted that obtaining a full air pollution permit is a long process, he said, and "there are no plans so far" for expansion of the plant.

Colby says the requested increase is in line with other car assembly plants and the agency's staff has recommended it be approved.

The bureau will take public comment on VW's request at a meeting Dec. 3.