Forecasters say air pollution levels will reach the code-red danger zone today for the first time this year, soaring high enough to be unhealthy for everyone by midafternoon.

Hot weather is expected to push concentrations of ground-level ozone, the main ingredient in smog, to 128 parts per billion in Central Maryland. Forecaster Matthew G. Seybold of the state Department of the Environment said westerly winds are carrying pollutants from the Ohio Valley into the region, and ozone levels might remain high tomorrow.

Code-red ozone levels can cause coughing, burning eyes and chest pain in healthy people. It is especially dangerous for children, the elderly and people with chronic respiratory or heart problems. New research suggests repeated exposure to high-ozone levels increases children's asthma risk.

MDE officials recommend staying indoors as much as possible and avoiding outdoor exercise today. The agency also asks residents to limit driving, postpone lawn mowing and refuel cars after dark.

Ground-level ozone is a colorless, odorless gas created when fumes from vehicles, lawn mowers, boat engines, industrial smokestacks and other sources cook in the heat and sunlight of summer days. Maryland has some of the nation's worst ozone pollution because contaminants from power plants and factories in the Ohio Valley blow into the region and mingle with tailpipe emissions from local traffic.

Last year, Maryland had 10 code-red days, which equals the past decade's annual average.

Sunday and yesterday were the first code-orange days of this year, with pollution heavy enough to cause problems for children and the elderly. MDE ozone specialist Robert Maddox said cool, cloudy, windy weather last month postponed smog formation, which normally begins at that time.