Some people are more sensitive to air pollution than other people. Different people can be sensitive to different air pollutants. For example, ozone might make you cough. Particulate matter may not bother you, but it may make your grandmother cough and need to rest.
One sensitive group is people with asthma. Asthma is a disease that can make it hard to breathe. If people who have asthma are careful and do what the doctor tells them to do, they may never have trouble breathing.