For the third day in a row, the city of Atlanta (home of achoo! ALLERGY) faces a Code Red smog alert, which means that the air is unhealthy for everyone.

With temperatures in the high 90s and heat indexes over 100, ozone levels have soared. Ozone, the main component of smog, is classified as a health hazard by the Environmental Protection Agency. The formation of ozone requires dry heat, and more heat means more ozone. A 10-degree rise in temperature doubles the number chemical reactions that produce ozone.

According to the Atlanta Journal-Constitution, the air also contains high amounts of soot, dust, and other particulate pollutants.

This is the smoggiest summer Atlanta has seen in four years, and the Atlanta Allergy & Asthma Clinic has witnessed an increase in respiratory problems. Children, the elderly, and people with respiratory conditions are most vulnerable to problems caused by air pollution. Everyone should limit outdoor activity during Code Red smog alerts.

A 1999 ScienceDaily article describes Atlanta as an ‘urban heat island,’ based on a NASA study. Due to the removal of trees and paving of land, heat-absorbing materials (like roofs and roads) hold onto the heat and keep the city hotter than surrounding rural areas.