A combination of wood fires and a few days of cold, still weather has again brought poor air quality to the Columbia Valley area in northern Whatcom County.

A Northwest Clean Air Agency monitor has detected air in the unhealthy range for fine particles periodically since Sunday, Dec. 30, 2012, deteriorating to very unhealthy since New Year's Day.

Conditions are expected to improve Thursday evening, Jan. 3, as rain is expected. But air quality often is worse in the evenings because more people are home using wood stoves, and cold weather combined with the nearby mountains traps smoke close to the ground.

Columbia Valley residents are asked to refrain from burning - including burning wood for heat and recreation - when conditions are poor. People can check air quality conditions at this nwcleanair.org site before lighting wood stoves.