A high-pressure system lodged over the region is holding cool, still air near ground level, trapping pollutants from wood stoves, fireplaces and outdoor burning.
The National Weather Service is calling for the high-pressure system and stagnant air conditions to weaken a bit Friday, but to return and remain over the region from Friday evening through Monday.
Overall, air-pollution levels are on the rise, which could lead to a mandatory burn ban later this week, clean-air agency spokesman Dan Nelson said.
For now, residents are asked to not burn wood to heat their homes unless they have no other source of heat. All land clearing burn permits have been cancelled until the weather conditions change to allow for greater ventilation and dispersal of smoke.
If residents do need to use wood heat, they are asked to limit their fires to midday, when air ventilation is greatest. The air inversions that allow the smoke to stay near ground level are strongest in the early-morning and late-evening hours.
On Thursday, air quality in the Lacey area was approaching unhealthy conditions in the morning, but it improved considerably by nightfall.
Burning wood creates smoke composed of small, even microscopic, particulate matter that can lodge in the lungs and respiratory system. The air pollutants can increase the likelihood of breathing problems, including asthma attacks, and cause extra problems for people with heart and lung disease.
Among the populations most vulnerable during stagnant air alerts are people with diabetes, children and people older than 65.
The state Department of Health recommends that people who are sensitive to air pollution limit their time spent outdoors, especially when exercising.
John Dodge: 360-754-5444
jdodge@theolympian.com
