AQI above 400 can harm the lungs, heart and blood vessels

Air quality above an AQI of 400 is highly hazardous, and prolonged exposure can affect more than the lungs.

Fine particles known as PM2.5 can travel deep into the lungs and may enter the bloodstream.

They can trigger inflammation and oxidative stress, causing symptoms such as coughing, wheezing, chest tightness and throat irritation.

Continued exposure can reduce lung function, worsen existing respiratory illnesses and raise the risk of respiratory infections.

Older adults and people with asthma, heart disease, diabetes or high blood pressure face greater risks because their bodies may be more vulnerable to pollution.

The effects can include worsening breathing problems and cardiovascular complications.

People in these groups should take extra care during severe pollution episodes; the available information does not specify what happens next.