Poor air quality is affected by high ozone levels, which are dangerous for anyone with respiratory concerns, and particle pollutions, which contribute to stroke and heart attack risk. HPA indicates a High Pollution Advisory, while the acronym USG stands for Unhealthy for Sensitive Groups. According to the Environmental Protection Agency’s airnow.gov, sensitive groups include older adults, children, active adults, and people with lung disease, such as asthma. So for a number of days this month, it seems just about everyone should have stayed indoors. Who knew?