Air Quality and Forecasts

To ensure the safety of our members, we monitor air quality. Ahead of a paddle on a “Spare the Air” day, we consult various air quality websites to assess air quality conditions.

We reference multiple sources as they occasionally present differing data. We’ve found the Bay Area Air Quality Management District’s (BAAQMD) historical figures to be very precise, and PurpleAir’s forecasts to be dependable.

To make informed decisions, we combine air quality readings with wind and weather forecasts. We then consult with our coaches to determine the best course of action.

Our threshold is an Air Quality Index (AQI) of 101 (PM2.5, Unhealthy for Sensitive Groups), at which point the decision to train rests with the coaches. If the AQI exceeds 150 (PM2.5 Unhealthy), training is automatically suspended.

PurpleAir’s laser sensors use a preset constant to estimate particle density. However, as wood smoke particles (common in the Bay Area) are less dense than typical PM 2.5 particles, this can lead to inflated AQI readings. Therefore, applying the LRAPA conversion, suggested by Adrian Dybwad, is crucial.

Limited coverage and information may have lag time. 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 refers to fine particulate matter pollution. In the Bay Area, PM2.5 is predominantly a winter issue, largely due to wood burning.