The Environmental Protection Agency (EPA) has issued an advisory urging residents in several parts of California to stay indoors due to unhealthy levels of fine particle pollution, specifically PM2.5. This advisory, effective as of February 22, 2026, at 4:30 a.m. ET, highlights elevated pollution levels in areas such as Portola, Cromberg, Sattley, the Sierra Valley, Plumas National Forest, Mammoth Lakes, Mono Lake, Whitmore Hot Springs, and the Silver Divide. PM2.5 particles, smaller than 2.5 micrometers, pose significant health risks as they can deeply penetrate the lungs and bloodstream, exacerbating conditions like asthma and causing symptoms such as chest tightness and shortness of breath.