Winter in Salt Lake County inevitably brings periods of temperature inversions, leading to poor air quality. When this happens, one of the primary concerns is the health of students who go outside for recess.
In these conditions, schools follow the direction of the Utah Department of Health for when to keep students indoors for recess. The graph below shows the points on the PM2.5 index at which groups of students are kept inside for recess. Current PM2.5 levels can be found at http://air.utah.gov/.
Sensitive students may include those with: asthma, cystic fibrosis, chronic lung disease, congenital heart disease, compromised immune systems, or other respiratory problems. Respiratory symptoms may include: coughing, wheezing, shortness of breath, and chest tightness.
Parents, with the advice of their health care provider, should inform the school if their child is part of a sensitive group who should have limited outdoor physical activity when air quality is poor.
This post was taken from http://www.graniteschools.org/blog/2016/01/05/q-during-inversions-how-do-schools-determine-when-to-keep-kids-inside-for-recess/