Wildfires are unplanned, destructive fires that rapidly spread out of control, especially in wilderness or rural areas. They can be started by lightning, human activity, sparks from falling rocks, or volcanic activity. They can also be started by fire that escapes from prescribed fires that are set to manage forests or agricultural lands.
Wildfires can be a threat to human and animal life, natural resources, and property. Smoke from wildfires can be a threat to human health. Other harmful effects that can follow wildfires include erosion, landslides, introduction of invasive species, and changes in water quality from sediment, burned debris, and chemicals.
Wildfire smoke is made up of a complex mixture of gases and fine particles from burning trees and other plant materials. The biggest threat to human health from wildfire smoke comes from the smokes fine particles, which are a category of particulate matter. The smoldering phase of a wildfire can continue to result in very high fine particle emissions.
Gases found in wildfire smoke include aldehydes, carbon monoxide, dioxin, nitrogen oxides, ozone, polycyclic aromatic hydrocarbons, volatile organic compounds, and heavy metals such as mercury. Smoke also contains acrolein, formaldehyde, and benzene, but at much lower concentrations than fine particles and carbon monoxide. Benzene, dioxin, formaldehyde, polycyclic aromatic hydrocarbons, and some volatile organic compounds are known or reasonably anticipated to be carcinogens.
When forests burn from wildfires, the carbon they store can be released back into the atmosphere as carbon dioxide.
Exposure to wildfire smoke can cause reduced lung function, bronchitis, wheezing, coughing, shortness of breath, tightness in the chest, chest pain, scratchy throat, runny nose, irritated sinuses, headaches, and stinging eyes, nose, and throat.
Older adults, children, and people with heart or lung disease are more likely to be affected by wildfire smoke. Exposure to wildfire smoke may worsen symptoms of asthma, respiratory allergies, and chronic obstructive pulmonary disease (COPD).
