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Air Quality and Forecasts

Ahead of a paddle on a Spare the Air day, we use multiple air quality sites (see below) to monitor air quality.

We use several sources because now and then, they don’t align. We have found BAAQMD historical numbers are very accurate, and BreezoMeter’s forecast is reliable.

We take the air quality numbers, combined with wind and weather forecasts, to make an educated guess and then check in with the coach(es) and ask how they want to handle it.

The ceiling is AQI 101 (PM2.5, Unhealthy for sensitive groups) it’s the coaches’ decision to train. If AQI is 151+ (PM2.5 Unhealthy) the club automatically suspends training.

Spare the Air

Bay Area Air Quality Management District (BAAQMD)




Use with LRAPA enabled. The laser sensors used by Purple Air rely on a hard-coded constant that represents the average density of the particles it is detecting. Because wood smoke particles are less dense (1.5 g/cm³) than typical PM 2.5 particles, the resulting AQI values are too high. This is the reason that LRAPA conversion is necessary. Thanks to Adrian Dybwad.

San Francisco Bay Area Current Outlook

Limited coverage and information may have lagtime. AirNow actually does something more complicated than a 1-hour average that is delayed by up to 3 hours, but the basic idea holds: AirNow data is averaged over a longer time period and will be delayed compared to PurpleNow.


PM2.5 is a term for fine particulate matter pollution.  PM2.5 is primarily a problem in the wintertime in the Bay Area, when wood-burning constitutes the major source.

Hourly Measurements

Each cell in this chart shows the estimated hourly Air Quality Index (AQI) values for PM2.5.

As established by the U.S. EPA, the AQI for PM2.5 is based on 24-hour concentrations, so hourly readings are only estimates.

The column at the far right shows the AQI value for the day, based on the 24-hour average concentration. (For the current day, this right-hand column will not appear, since the full data for the 24-hour day is incomplete.)

If the number in the far-right column is greater than 100, it means that PM2.5 levels were over the federal health standard.  Values between 101 and 150 in the far right column mean that air quality was in the Unhealthy for Sensitive Groups category for the day.  If the value in the far right column is greater than 150, that means air quality was in the Unhealthy category.