In sensitised asthma patients, the immediate bronchospastic response to PM2.5 and ozone can begin within 15–30 minutes of outdoor exposure. The more clinically dangerous late-phase inflammatory response peaks 4–8 hours after exposure — meaning patients often feel relatively stable during the day and deteriorate significantly overnight. At Pulmovista Clinics, I advise all asthma patients to monitor through the night following any significant outdoor exposure during an AQI 300+ event, regardless of how they feel in the evening.
