@SmartAirFilters This is exactly the kind of message that should be shared more widely. Lower PM₂.₅ exposure is better, even when concentrations are already relatively low. This study is far from an isolated finding: a large body of research has documented adverse health effects at concentrations lower than previously understood. This accumulating evidence is precisely why the WHO lowered its annual PM₂.₅ guideline from 10 to 5 µg/m³ in 2021. The WHO specifically noted that the change primarily reflected new evidence of health effects occurring at low levels of exposure. The same direction is reflected in the U.S.: in 2024, the EPA strengthened its annual health-based PM₂.₅ standard from 12 to 9 µg/m³, based on the available health science. “Low” does not mean harmless. No threshold has been identified below which PM₂.₅ causes no adverse health effects. That means reducing exposure further can still matter even when the air already seems relatively clean. That is why communicating findings like these matters: people need to know that reducing particulate exposure isn't only worthwhile when pollution is obviously high. Even relatively small reductions at lower concentrations can matter for public health. This is also why, in my own place, I aim to keep PM₂.₅ as low as possible. My Qingping Air Monitor Lite normally reads 0 µg/m³, and when I cook, I monitor PM₂.₅ closely and try to bring it back down as quickly as possible. Cooking can cause surprisingly high PM₂.₅ spikes indoors, something many people only discover once they start monitoring their air, and which has led many of us to change our cooking and ventilation habits. To put this into perspective: if PM₂.₅ averages 5 µg/m³ for 23.5 hours, a single 30-minute cooking episode averaging 250 µg/m³ is enough to raise the entire 24-hour average to about 10 µg/m³. That is why I don't dismiss short-term exposure just because the air is clean most of the day. Keeping PM₂.₅ low also means paying attention to those temporary but significant indoor spikes.