PM2.5 or AQI: which number your state uses
California writes its smoke rule in AQI. Oregon and Washington write theirs in concentration. They are not interchangeable.
AQI is an index derived from a pollutant concentration through breakpoints that EPA revises. PM2.5 is the concentration itself, in micrograms per cubic meter. California smoke thresholds are written in AQI, Oregon and Washington in PM2.5. Recording only AQI on an Oregon or Washington site leaves the smoke rule with nothing to evaluate, and a stale AQI conversion can put a day in the wrong tier.
Takeaways
- Say which smoke metric each of your states requires.
- Explain why the AQI conversion is not a fixed relationship.
- Pull both numbers from a source you can name.
- Recognize when a regional reading is too coarse for your site.
They measure two different things
Which number each state reads
Getting both numbers from a source you can name
When a regional reading is too coarse
Frequently asked questions
- Can I convert my AQI reading to PM2.5 for an Oregon log? The conversion is possible but lossy, because each AQI value maps to a range of concentrations. If the monitor reports concentration, record the concentration. Converting backward from a rounded index is weaker evidence.
- Which AQI does California mean when several pollutants are elevated? The AQI for PM2.5 specifically. On a wildfire smoke day PM2.5 is usually the driving pollutant anyway, but the rule is written to PM2.5 rather than to the overall AQI.
- Are low-cost sensors acceptable? They can be useful, especially where the nearest official monitor is far away. Know the limitations, apply any correction the manufacturer recommends for smoke, and record that the reading came from a sensor rather than a reference monitor.
- What should I record if I work in all three states? Both metrics on every smoke day. They come from the same monitor in one lookup, and it removes the risk of a rule going unevaluated when a crew crosses a line.