Cumulative vs acute exposure

Air-pollution health effects split into two broad regimes. Acute effects come from short, high exposures: an asthma flare on a heavy smoke day, eye and throat irritation from a cleaning-product VOC pulse. Cumulative effects come from sustained low-to-moderate exposure over years: cardiovascular disease, lung-function decline, and higher mortality risk. The two regimes have different drivers and respond to different interventions.

Dose connects a concentration to a biological effect. For air pollutants it is roughly concentration × time × breathing rate, and for a resting adult the breathing term is fairly constant, so the useful number is exposure: concentration multiplied by time. One hour at 250 µg/m³ of PM_2.5 and ten hours at 25 µg/m³ have the same area under the curve. They are still not interchangeable, because biology responds to both the area and the peak: high short spikes drive irritation and asthma attacks, while long, low exposure drives slow damage.

The PM_2.5 literature is unusually clear on this. The Lancet Global Burden of Disease analysis attributes most PM-related deaths to long-term exposure, the AHA scientific statement quantifies cardiovascular risk per 10 µg/m³ of long-term average, and the Harvard Six Cities study linked long-term particle levels to mortality. No safe threshold has been identified for the chronic effects. That is why guidelines come in pairs: WHO 2021 sets 15 µg/m³ for 24 hours and 5 µg/m³ annually; EPA sets 35 µg/m³ for 24 hours and 9 µg/m³ annually. A home can stay under the 24-hour value every day and still sit above the annual guideline.

Exposure also stacks across pollutants. Guidelines are written one pollutant at a time, but the body experiences them together: several readings in their moderate bands at once (PM_2.5, the NO_x index after a gas-stove dinner, high humidity in a closed-up room) can add up to a load none of them carries alone, and some combinations, such as ozone with fine particles, may act more than additively. Warm rooms also off-gas more VOCs. The practical rule: start with the action that lowers the most readings at once. Running a vented range hood and opening a window can lower NO_x, PM_2.5, and humidity together; a HEPA purifier lowers only particles. See interaction effects and time scales of air quality.

Both regimes show in your data. Current readings and the last hour answer "is anything happening right now?" History over days and weeks shows your typical pattern and where it sits against long-term guidelines: a 30-day PM_2.5 average of 18 µg/m³ is well above the WHO annual guideline, even if no single day looked remarkable. Some limits remain: individual susceptibility varies, and the device doesn't measure ozone or NO₂ concentrations directly, so outdoor ozone comes from the outdoor feed.

This is environmental information, not medical advice. Terrestream's readings help you make decisions about the air in your space. They do not diagnose conditions, interpret symptoms, or replace conversations with your physician. If symptoms persist, worsen, or coincide with a known exposure, talk to a healthcare professional. See what Terrestream's advice covers.