Thursday, July 29, 2021


Air quality advisory extended as unhealthy conditions expected intermittently

The Colusa County Air Pollution Control District is extending an air quality advisory – initially issued on Aug. 3 – for the second time, as wildfires burning in Northern California continue to produce significant smoke impacts in Colusa County communities.

In a press release issued on Monday afternoon, Colusa County Air Pollution Standards Officer Donald Kitamura said that smoke impacts from the fires may continue throughout the week. While the Colusa County Air Pollution Control District reports that air quality conditions are currently in the moderate range on the Environmental Protection Agency’s Air Quality Index (AQI), those conditions could quickly change from moderate to unhealthy – which may be the pattern for the next few days.

The AQI is an index that government agencies use to report on daily air quality, which quantifies how clean or polluted air in a given location is, as well as the potential associated health effects that might be experienced within a few hours or days after breathing polluted air. The EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. Ground-level ozone and airborne particles are the two pollutants that pose the greatest threat to human health in the country.

The AQI spans a range of values from 0 to 500, and the higher the AQI value, the greater the level of air pollution and the greater the health concern. The AQI is divided into six categories: good (AQI values from 0 to 50, where air pollution poses little or no risk); moderate (51 to 100, where air quality is acceptable, but for some pollutants there may be a moderate health concern for a very small number of people); unhealthy for sensitive groups (101 to 150, where air quality is unlikely to cause issues with the general public, but sensitive groups like children, older adults, and those with heart or lung disease are at greater risk); unhealthy (151 to 200, where the air quality is such that everyone may begin to experience adverse health effects, and members of sensitive groups may experience more serious effects); very unhealthy (201-250, which would trigger a health alert signifying that everyone may experience more serious health effects); and hazardous (301 to 500, which would trigger health warnings of emergency conditions, in which the entire population is more likely to be affected).

“It’s been pretty bad,” Deputy Air Pollution Standards Officer T.J. Gomez said early on Monday afternoon. “Conditions on Friday night into Saturday morning were pretty bad, and were actually unhealthy for everybody. We’ve been remaining in the unhealthy for sensitive individuals since then. Right now – it’s amazing to say – but we’re actually in the good range at this moment; but wind shifts or inversions can change anything from time to time.”

Gomez said that if you can see smoke, and particularly if you can smell it, it’s probably a good idea to limit outdoor activity.

With their press release, the Colusa County Air Pollution Control District also sent an EPA wildfire air quality guide, which describes how to use visibility to estimate fine-particulate (smoke and dust) air pollution, also known as PM2.5 levels. When visibility is at 11 miles or more, PM2.5 levels fall into the “good” range. When it is between six and 10 miles, PM2.5 levels are in the “moderate” range. Visibility between three and five miles falls in the “unhealthy for sensitive groups,” while visibility between 1.5 and 2.75 miles falls in the “unhealthy” range. When visibility is less than 1.25 miles, the PM2.5 levels fall into the “very healthy” or “hazardous” range.

“When it gets into the unhealthy range, where there’s some sort of sports practice or something along those lines, you should consider canceling it or rescheduling it,” Gomez said.

At 3 PM on Friday, Colusa’s monitoring station measured PM2.5 (fine particulate matter pollution) levels to be at 155 – the bottom of the unhealthy range. PM2.5 levels on the Cortina Rancheria were measured as being slightly higher at 178.

“The further west you get in the county, air quality is going to get worse,” Gomez said. “The west side of the county might be a little higher than we are right now.”

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