Air Quality in the Morning Vs Nighttime Researchers discovered that particulate matter concentrations are greater in the morning and at night. It is especially active between 7:00 and 10:00 a.m. and 9:00 and 11:00 p.m. (LST). On the other side, it is lowest in the afternoon, particularly from 3:00 and 5:00 PM (LST).

for the pollutant. AQI values at and below 100 are generally considered to be satisfactory. When AQI values are above 100, air quality is considered to be unhealthy, at first for members of populations at greatest risk of a health effect, then for the entire population as AQI values get higher (greater than 150).

The Washington Department of Ecology (Ecology) uses the Washington Air Quality Advisory (WAQA) to inform people about the health effects of air pollution. Ecology developed the WAQA to tell people when air quality is unhealthy so they can protect themselves. The WAQA is not a regulatory tool. 0-50 Air quality is good.