The National Weather Service has issued an air quality alert for the Chicago metropolitan area and northwest Indiana, effective until Wednesday night. This alert is prompted by the forecast of elevated ozone levels, which are expected to reach or exceed the 'unhealthy for sensitive groups' category. The Illinois Environmental Protection Agency (IEPA) has declared an Air Pollution Action Day, indicating that sensitive individuals, particularly those with respiratory conditions such as asthma, should limit prolonged outdoor activities. As of Tuesday afternoon, the air quality index showed 'good' ratings for areas like Aurora, Elgin, Chicago, Joliet, and Will County, while regions including Lake County and various suburbs reported 'moderate' air quality. The situation is expected to worsen, with forecasts predicting that by Wednesday, all reporting areas in Illinois will fall into the 'moderate' or 'unhealthy for sensitive groups' categories, necessitating caution for vulnerable populations.