Where is Sonoma’s Purple Air sensor?

You can have one reading air quality levels on your property for around $250.|

Purple Air is a community air monitoring system with a website and map that launched in November 2015. Its map displays points using the Federal Environmental Protection Agency (EPA) Air Quality Index (AQI) scale. The AQI allows comparison for different pollutants with an easy to visualize color scheme. The air goes from good green air to yellow to orange to red to purple air, or even hazardous maroon air.

Over the course of the past week, the Purple Air website has emerged as the defacto “gold standard” for air quality measurements, and it is its index that is now being used by the Sonoma County Office of Education to monitor and determine air quality.

Some towns, like Glen Ellen, do not have a Purple Air monitor and must rely on the nearest possible monitor location. Sugarloaf Ridge State Park, north of Kenwood, installed a monitor last August.

Downtown Sonoma has one monitor, located on private property at the corner of Fifth Street East and Napa Road.

But anyone can purchase a sensor for around $250 and join the network of sources that Sonoma's index reading pulls from.

The small white sensor is around the size of a yogurt container It uses a fan to draw air past a laser, causing reflections from any particles in the air. These reflections are used to count particles in six sizes between 0.3µm and 10µm diameter.

Readings are then uploaded to the cloud every 80 seconds or so where they are stored for download and display on the Purple Air map. The values are average every 20 seconds and graphically displayed on the Purple Air website.

Purple Air sensors are easy to install, according to the company, requiring a power outlet and WiFi. They are typically placed on the side of a house, a few feet above face level.

The sensor uses WiFi to report in real time to the Purple Air map. www.purpleair.com.

UPDATE: Since this article was filed, Sonoma Valley Hospital has had both an exterior and interior monitor go online with Purple Air.

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