Smoke from wildfires around the Bay Area has led air regulators to extend a “Spare the Air” alert through Wednesday, which will be the 23rd consecutive day of poor air quality in the region.
The streak represents the longest continuous period of alerts ever issued by the Bay Area Air Quality Management District (BAAQMD). The previous record of two weeks was linked to smoke from the 2018 Camp Fire.
As containment of the fires has increased, the air has improved. (At 10 a.m. Tuesday the air quality index measured by BAAQMA at Aquatic Park in Berkeley was reported as being in the “good” green zone at 47 PM2.5, but you wouldn’t have guessed that by the hazy skies and blurred orange of sun greeted residents when they woke up.) But because the fires are still burning, the BAAQMD is still expecting smoke to create pockets of unhealthy air.
In the Bay Area, residents have become used to the ritual of checking air quality maps for a possible escape from the smoke, if there is one, when fires burn nearby forests and chaparral.
During the Camp Fire, AirNow, an air quality website created by a partnership of states, the federal government, Canada and Mexico, crashed because it could not handle so many people flocking online to put numbers to what their noses were telling them: The air smells really bad.
But this year, users are faced with a different problem. Official sites, maintained by air regulators, and crowdsourced maps like PurpleAir show different air quality readings.
So, what’s the deal?
Broadly put, PurpleAir provides more localized, current and less accurate readings than AirNow.
A couple of weeks ago, the EPA and the U.S. Forest Service launched a pilot project of what some may consider to be the Holy Grail of air quality maps: combined readings taken from PurpleAir’s low-cost sensors and those from official government monitoring devices, all in a single map; the circles represent official government monitors, the squares indicate PurpleAir sensors, and the triangles show temporary monitors set up by federal agencies.
PurpleAir readings and those from government sensors like the ones maintained by the BAAQMD differ in several key ways: speed, accuracy and placement.
Users of PurpleAir can toggle between real-time data and readings averaged over the last 10 or 30 minutes. The data comes from the commercial sensors the company sells, which members of the public install on porches, yards and other neighborhood sites. The readings can be helpful for people deciding whether to go for a walk or engage in other outdoor activity. (Remember to deselect “indoor sensors” to see outdoors-only readings.)