CHICAGO -- Monday was an Air Pollution Action Day and Tuesday's been declared on too. Health officials recommend that young people and seniors stay inside but many Chicago residents are ignoring the warnings.

CHICAGO -- An Air Pollution Action Day has been declared for Monday and Tuesday in the Chicago area and northwestern Indiana.

A notice for the day was issued to alert residents that low winds and high temperatures have the potential to produce elevated levels of air pollution, particularly ozone, which could reach unhealthy air quality levels for sensitive populations, particularly people with respiratory or pulmonary disorders, Partners for Clean Air said in a news release on Sunday.

An Air Pollution Action Day is declared when weather conditions are such that widespread ozone or fine particulate matter levels are expected to be at or above the "unhealthy for sensitive groups" category of the Air Quality Index, the release said.

A high-pressure system, which may contribute to an elevated level of air pollution, had been encircling the Chicago area and northwestern Indiana late Sunday and was expected to stay around through Tuesday, according to National Weather Service meteorologist Nathan Marsili.

The areas should expect partly cloudy skies with highs in the low 90s on Monday, Marsili said. Winds should be moving in from the south between 5 and 10 mph on Monday and Tuesday, a National Weather Service forecaster, who declined to be identified, said.

By Wednesday and Thursday, cooler temperatures and a low- pressure system should be moving into the Chicago area and northwestern Indiana, eliminating the threat of elevated pollution levels, Marsili said.

The Air Pollution Action Day has been designed to include both ozone and particulate matter pollution and can be called at any time throughout the year.

During an Air Pollution Action Day, residents are asked to reduce contributions to ozone and particulate matter pollution by following "Green Actions" in ways that include:

-- Rideshare use I-PASS, walk or bike.

-- Take the Chicago Transit Authority, Metra and Pace.

-- Avoid excessive vehicle idling and abrupt starts.

-- Postpone lawn-mowing, gardening chores and recreational activities that use gasoline-powered equipment.

-- Use a charcoal chimney or electric starter instead of lighter fluid when barbecuing.

Ozone forms as a result of industrial and vehicle emissions of nitrogen oxides and volatile organic compounds in the presence of sunlight and warm temperatures. Particulate matter consists of tiny airborne particles that are often less than one-hundredth the width of a human hair, the news release said.