Qualité de l’air à Sunnyvale

How is Sunnyvale air quality today?

Sunnyvale air quality is generally considered healthy to breathe. In 2019, the city received mixed ratings after failing to pass federal targets for 24-hour PM2.5 despite having met other measures for annual PM2.5 and ozone.¹ The excess of allowable 24-hour PM2.5, or number of “unhealthy” PM2.5 days, was largely the result of an unpredictable emission source that’s difficult to manage – wildfires.

Wildfires tend to give way to Sunnyvale’s worst PM2.5 pollution events. In 2019, Sunnyvale air quality averaged an overall US AQI rating of “good,” indicating that air quality typically poses little to no health risk. Sunnyvale additionally met the more stringent World Health Organization (WHO) target for annual PM2.5 exposure of 10 μg/m³, with an average of 6.6 μg/m³. Annual averages, however, smooth over unhealthy, dangerous pollution events. Sunnyvale, for example, experienced a number of unhealthy pollution days as a result of wildfire smoke. These events are not well accounted for by its annual PM2.5 average.

The Kincade wildfire of November 2019 caused a significant breach of the norm, with a monthly PM2.5 average of 16.7 μg/m³ (“moderate”) roughly three times the normal monthly average.

From 2016 to 2018, Sunnyvale and greater Santa Clara County experienced 14 “orange” PM2.5 days described as “unhealthy for sensitive groups” and 11 “red” PM2.5 days described as “unhealthy” for the general public. The majority, if not all, of these days resulted from wildfire smoke.

As a result of the high frequency of these PM2.5 pollution spikes, Sunnyvale and the greater San Jose-San Francisco-Oakland area rank 3rd nationally for worst 24-hour particle pollution out of 217 metropolitan areas.

Sunnyvale air quality also suffers from the occasional high ozone event. While it met federal targets in 2016 to 2018, the city still experienced 4 “orange” ozone days and 3 “red” ozone days during this period. Moreover, the previous 4 years exceeded this target, albeit only slightly.

In the 2016 to 2018 monitoring period, the San Jose-San Francisco-Oakland area, of which Sunnyvale is a part, ranked 8th nationally for worst ozone out of 228 metropolitan areas. This rating may, however, be more attributable to San Francisco air quality and Oakland air quality, which consistently fare worse than Sunnyvale.

Air pollution is dynamic and fast-changing, often varying throughout the day. Despite generally healthy air quality, it’s important to track real-time data in order to protect oneself from adverse health effects. Refer to the top of this page for Sunnyvale’s forecast air quality data.

When will Sunnyvale air quality improve?

Improvements to Sunnyvale air quality will depend on the effective regulation and management of the city’s largest emitters: mobile sources, wildfires, and neighboring cities.

At the top of that list, mobile sources, including cars, heavy-duty trucks, planes, and ships from nearby ports, represent the largest source for city-wide emissions, a common trend across US cities. In nearby San Jose, motor vehicles alone account for roughly 30% of fine particulate matter (PM2.5) and the vast majority of nitrogen oxides in the air (NO_x), a precursor to ozone pollution formation.²

The recent advent of incentives for and growing popularity of more fuel-efficient, low-emission vehicles represent a great opportunity for improving air quality both in Sunnyvale and across the nation.

Sunnyvale sits just 12 miles to the west of San Jose, the heart of Silicon Valley. The presence of such an affluent and tech-savvy demographic contributes to forward and adaptive purchasing by the community at large.³ It may be of no surprise that San Jose has the highest ownership of registered electric vehicles nationally at 21 percent. This number, moreover, is growing rapidly, and the government aims to reach a 61 percent market share by 2030.⁴

As evidenced by the 2020 COVID-19 lockdown, which shuttered business and discouraged non-essential business and travel, it is possible to greatly reduce air pollution levels in Sunnyvale by reducing the number of gas-powered vehicles on the road. The Bay Area Air Quality Management District (BAAQMD) estimates that during the lockdown, traffic congestion in San Jose fell by 70 percent, directly contributing to a 20 percent reduction in PM2.5 and 40 percent reduction of nitrogen oxides, an ozone precursor pollutant.

Wildfires, though unpredictable and relatively short-lived, tend to contribute to Sunnyvale’s worst pollution events where air quality levels reach “unhealthy” or worse. Sunnyvale’s fluctuating pollution levels year over year tend to have a strong correlation with the severity of that year’s wildfire season. San Jose’s air quality levels, for example, rose by 19.2 percent from 2017 to 2018, nearly matching an increase in the number of acres burned nearby. As regional and global temperatures continue to climb with climate change, wildfires are expected to become both more frequent and severe. This trend could balance or even counteract gains made by transitioning to cleaner energy and transport.

The city’s location, moreover, near the large cities of San Jose, San Francisco, Oakland, and large suburban sprawl provides additional challenges in achieving improved air quality. Emissions created in any one of these cities is easily carried by wind, contributing to Sunnyvale air pollution levels. Working with the Bay Area community to tackle these challenges together will be important for Sunnyvale’s overall success in reducing city-wide pollution levels.

Where is Sunnyvale smoke coming from?

Sunnyvale smoke, described as visible pollution from burning substances, tends to come from wildfires in the Bay Area. There is a history of wildfires burning on all sides of Sunnyvale. In August of 2020, for example, CZU Lightning Complex burned to the west near the Pacific Coast, the Coyote Fire and Dolan Fire burned just to the south, the SCU Lightning Complex to the east, the Claremont Fire to the north east, and the LNU Lightning Complex to the north.⁵

Use Sunnyvale’s air pollution map to discover emissions and events that may be contributing unhealthy air. Sunnyvale's live air quality map animates wind carried pollution in vibrant AQI colors, revealing the big picture behind real-time pollution levels.

How bad is Sunnyvale ozone pollution?

While Sunnyvale met federal attainment levels for ozone in the most recent monitoring period of 2016 to 2018, the greater region that includes San Jose, San Francisco, and Oakland was ranked 8th nationally for worst ozone out of 228 metropolitan areas.

Ozone is known as a secondary air pollutant – rather than being emitted directly into the air, it is formed from primary pollutants reacting in sunlight. As a result of this property, it is often considered one of the most poorly regulated pollutants in the US. Warm and dry locations with abundant sunshine have even greater challenges. For ozone to form, conditions should be sunny, with temperatures generally over 84 degrees. There are 78 days a year, from April to October, that meet these ideal ozone conditions in Sunnyvale.⁶ As climate change raises regional temperatures, many scientists and public health experts fear increased ozone levels as well.

Ozone is a highly reactive gas that can contribute to lung damage and breathing difficulty. Short-term exposure can cause chest pain, coughing, shortness of breath, and lung irritation, while long-term exposure can put people at risk of ozone poisoning, lung cancer, lung scarring, and even early death.

Ozone levels in Sunnyvale tend to peak around the afternoon when direct sunlight is the strongest. Follow Sunnyvale’s real-time ozone levels at the top of this page to know when to avoid outdoor activity or heavy exertion.

How unhealthy is the wildfire smoke in Sunnyvale?

Plumes of smoke rising from wildfires across the Bay Area and greater California have been responsible for Sunnyvale’s most severe air quality advisories. Of the six pollutants the US Environmental Protection Agency (EPA) actively monitors and regulates, PM2.5 is of principal concern during these events. Other harmful air pollutants include PM10, carbon monoxide (CO), nitrogen dioxide (NO₂), and volatile organic compounds (VOCs).⁷ Ozone can be created when VOCs and NO_x released by wildfires undergo photochemical processing in sunlight and heat.

Breathing wildfire smoke has been connected to health outcomes ranging from respiratory tract irritation and chest pain to more serious effects like reduced lung function, pulmonary inflammation, bronchitis, exacerbation of heart and lung disease, heart failure, and even early death. While the consequences can be severe, most healthy children and adults will recover quickly due to the resilience of the human lungs. Certain life stages and populations, however, may experience more adverse effects. These individuals who are at greater risk of experiencing health effects from exposure to Sunnyvale wildfire smoke, include children, adults over 65, pregnant women, and people with pre-existing heart and lung conditions.

+ Article Resources

[1] American Lung Association. (2020). State of the air – 2020.
[2] Rogers P. (2020, March 23). Coronavirus: Bay Area air quality is improving as people stay home. The Mercury News.
[3] Medina M. (2019, June 17). New study shows spike In Bay Area electric car sale. CBS SF BayArea.
[4] Hase G. (2019, October 22). City of San Jose plans to double electric car charging stations with $14 million investment. San Jose Inside.
[5] Asperin A. (2020, August 24). Interactive map: Current California wildfires. KRON 4.
[5] Current Results. (2020). San Jose temperatures: averages by month.
[6] Urbanski S, et al. (2009).Chemical composition of wildland fire emissions. DOI: 10.1016/S1474-8177(08)00004-1