The weather forecast for Wednesday is good news for those of us who are sick of living in a city that smells like an fireplace, makes your eyes water, and gives you a headache. For those folks (which is pretty much everybody) the words “northwest winds” are key — that’s what we need to clean the junk out of the air, and that’s what the National Weather Service forecast calls for Wednesday.
The reason northwest winds are so important is that is the only place in the region where there are no wildfires. Right now, with the more typical southwesterly flow, the Treasure Valley is getting smoke from fires in California, Oregon and Nevada during the day, with smoke from local fires (the Springs and Trinity Ridge near Banks and Featherville) sliding down into the Boise area at night.
That’s why the Boise area had an orange air quality alert earlier on Tuesday, with an air quality index (AQI) of 140, according to the Idaho Department of Environmental Quality. That’s only 10 AQI points away from a red air quality alert, which means the air is unhealthy for everyone, not just sensitive groups.
Visibility was as low as 1 1/4 miles at the Boise Airport just before noon Tuesday, but it improved to seven miles by about 8:30 p.m. — due largely to 5 to 8 mph winds from the west and northwest. The Department of Environmental Quality said the AQI at 5 p.m. Tuesday was below 90, which is considered “acceptable” and posing a risk to only a small number of people.
Forecasts show those coveted northwesterly winds blowing through southwest Idaho by Wednesday afternoon. Once the daily inversion breaks up Wednesday morning, those winds should push some of that bad air out of the valley, National Weather Service meteorologist Beth Burgess said.
The low pressure system isn’t expected to move through the region until early Wednesday, but it is expected to be slightly cooler.
That northwesterly air flow might stick around through Friday, Burgess said.
The problem is that once the more regular southwesterly wind flows come back into the Treasure Valley, they will push all that smoke from the fires burning across the West back into the Boise area, so this week may only provide a temporary respite, Burgess said.
How does the AQI work?
The Idaho DEQ uses an air quality index (AQI) to report on the levels of five pollutants (small particulates, large particulates, ozone, carbon monoxide and sulfur dioxide). In the Treasure Valley particulates and ozone are usually the culprits during poor air quality days.
Think of the AQI as a yardstick that runs from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern.
For example, an AQI value of 50 represents good air quality with little potential to affect public health, while an AQI value greater than 300 represents hazardous air quality.
An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health.
When AQI values are above 100, air quality is considered to be unhealthy — at first for certain sensitive groups of people, then for everyone as AQI values increase.
To make it easier to understand, the AQI is divided into six categories:
Green — Good, 0-50: Air quality is considered satisfactory, and air pollution poses little or no risk.
Yellow — Moderate, 51-100: Air quality is acceptable; however, for some, pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.
Orange — Unhealthy for sensitive groups, 101-150: Members of sensitive groups may experience health effects. The general public is not likely to be affected.
Red — Unhealthy, 151-200: Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.
Purple — Very unhealthy, 201-300: Health alert — everyone may experience more serious health effects.
Maroon — Hazardous, 301-500: Health warnings of emergency conditions. The entire population is more likely to be affected.
