Air Quality in Sunnyvale, California — Live

Live readings from PurpleAir sensors across Sunnyvale — with free alerts the moment the air turns.

Live Sunnyvale AQI from nearby PurpleAir sensors loads when this page opens in a browser, along with a live sensor map covering Sunnyvale and Mountain View, Santa Clara, Cupertino, Los Altos.

Sunnyvale's outdoor air is good most of the year. It sits at the bay end of the Santa Clara Valley, close enough to the water that the afternoon breeze usually reaches it, and its bad days almost always arrive from somewhere else as smoke. What makes Sunnyvale unusual is not what floats over it but what is underneath part of it: a chlorinated solvent plume from the early chip industry that the EPA has been chasing since the 1980s, and that is still being monitored inside homes and schools today. It matters here because it is exactly the kind of air problem a particle sensor cannot see.

Canairy watches the sensors around your home, your kids' school, and everywhere else you care about, and tells you in plain English when the air changes enough to matter.

The plume under the San Miguel neighborhood is real, and these sensors cannot see it

EPA calls it the Triple Site: three former semiconductor plants in Sunnyvale, the Advanced Micro Devices site at 901/902 Thompson Place, the TRW Microwave site, and the Signetics site, plus a fourth area downstream of them called the Offsite Operable Unit. AMD used trichloroethylene and other solvents to clean and degrease parts between 1969 and 1992, and in 1982 a leak from an acid neutralization sump in the 901 Thompson Place building started the investigation that is still running. The worst groundwater sample EPA reports is 110,000 micrograms per litre of TCE at a well beside the neutralization tank.

The Offsite Operable Unit is the part with people living on it. EPA describes a single commingled plume roughly 4,000 feet long under about 100 acres north of Duane Avenue, extending past Highway 101, with four schools and more than 100 homes above it. Because TCE evaporates out of groundwater and can seep up into buildings, EPA began a vapour intrusion study there in 2015. In its 2019 five-year review it reported that more than 225 households and 40 school buildings had been sampled and more than 20 mitigation systems installed where indoor TCE exceeded the 2.0 micrograms-per-cubic-metre screening level. Those systems are mostly sub-slab depressurization, sealing and ventilation upgrades. As of March 2023 the Sunnyvale School District said recent EPA indoor air testing in the San Miguel neighborhood showed the air clean and safe, and that neighbourhood drinking water is not affected. Say the obvious part plainly: the map below reads fine particles, not solvent vapour. It will tell you about smoke. It will tell you nothing about TCE.

Sunnyvale sits at the bay end of the valley

San Jose is far enough down the Santa Clara Valley that cooling marine air often does not reach it. Sunnyvale is not. The city runs from Cupertino's foothills north to the bay shore at the Sunnyvale Baylands, and that northern half gets the ventilation the south end of the valley lacks. It is a real difference between two cities twenty minutes apart, and it is why Sunnyvale readings and San Jose readings can diverge on a hot, still afternoon.

The trade for that is traffic. Highway 101 crosses the city's north side, State Route 237 runs along the bay edge, and Lawrence Expressway cuts through the middle of it. If you live within a couple of blocks of any of them, your own street can read higher than the citywide number during the morning and evening peaks, which is the case for watching the sensor nearest you rather than a single figure for the whole city.

A second, bigger plume starts at the Moffett Field line

Sunnyvale sold the 1,000-acre bayside parcel that became Naval Air Station Moffett Field to the federal government for a dollar in 1930, and the base sits on the city's north-western boundary today as Moffett Federal Airfield. Immediately west of it is a separate and larger EPA case: the Middlefield-Ellis-Whisman Study Area, which covers part of Mountain View and part of Moffett Field, involves Intel and Raytheon among other parties, and which EPA describes as one of the largest Superfund vapour intrusion cleanups to date, with roughly 60 commercial and residential buildings at potential risk.

That one is not in Sunnyvale, and it is worth being precise about it, because the two get blurred together locally. Both are groundwater and indoor-air problems handled by EPA sampling inside buildings. Neither is something you diagnose from a rooftop particle sensor. If you want to know whether your specific address is in either study area, EPA's site pages and the school district's environmental testing page are the places to look.

Sunnyvale air quality FAQ

What is the air quality in Sunnyvale right now?

This page shows the current AQI for Sunnyvale, calculated from PurpleAir sensors across the city and updated continuously. Sunnyvale covers a lot of ground between the Cupertino foothills and the bay shore, and on a still day the two ends can read differently. The map below shows every live sensor so you can pick the one closest to your own street.

Why is there smoke in Sunnyvale today?

Almost always because something is burning well outside the city. Sunnyvale has no wildland inside it, so the smoke you see here has usually drifted in from a fire in the Diablo Range to the east, the Santa Cruz Mountains to the west, or somewhere much further north in California. On a cold, still winter evening the haze is more likely to be wood smoke from fireplaces settling near the ground. Either way the live reading on this page will tell you within minutes whether it is a close-the-windows situation or just a smell.

Does the Superfund contamination affect Sunnyvale's air quality readings?

No, and this is worth understanding. The Triple Site contamination is trichloroethylene and related solvents dissolved in groundwater, which can evaporate and seep into buildings through the slab. That is called vapour intrusion, it is measured by sampling indoor air, and EPA has installed mitigation systems in buildings where it exceeded the screening level. PurpleAir sensors measure fine particles in outdoor air. They are two completely different problems with two completely different instruments, and a good number on this page says nothing either way about TCE.

Has EPA found TCE in Sunnyvale's outdoor air?

In small amounts. EPA has sampled outdoor air in the Offsite Operable Unit regularly since January 2015 alongside its indoor sampling. Its 2019 five-year review reported that outdoor TCE levels were often low but showed periodic spikes of up to 3.6 micrograms per cubic metre, with the spikes trending upward over time, and recommended investigating whether they come from the groundwater treatment system and the mitigation vent stacks rather than from the plume itself. EPA announced in 2024 that it would review the Triple Site cleanup again.

What AQI level is unhealthy?

Under the US EPA scale, AQI 0–50 is Good and 51–100 is Moderate. From 101 the air is Unhealthy for Sensitive Groups — kids, older adults, and people with asthma or heart conditions — and above 150 it's Unhealthy for everyone. Canairy translates these numbers into a plain-English verdict, like whether to close the windows or move a workout indoors.

Is Canairy free?

Yes. The Canairy app is free to download and includes live air quality for all your saved places, plain-English verdicts, and free push alerts when the air crosses your threshold. A paid plan adds extras like SMS text alerts.

Get Canairy free on Google Play.