|1||White City, Utah|
|2||Del Aire, California|
|3||John Day, Oregon|
|6||Loma Linda, California|
|8||Klamath Falls, Oregon|
|9||San Bernardino, California|
|10||La Mirada, California|
(local time)SEE WORLD AQI RANKING
|2||The Hamlin School|
(local time)SEE WORLD AQI RANKING
12:16, Nov 26
live AQI index
|Air pollution level||Air quality index||Main pollutant|
|Good||11 US AQI||PM2.5|
|Open your windows to bring clean, fresh air indoors|
|Enjoy outdoor activities|
|Sunday, Nov 22|
Good 18 US AQI
|Monday, Nov 23|
Good 31 US AQI
|Tuesday, Nov 24|
Good 23 US AQI
|Wednesday, Nov 25|
Good 17 US AQI
Good 48 US AQI
|Friday, Nov 27|
Moderate 72 US AQI
|Saturday, Nov 28|
Moderate 94 US AQI
|Sunday, Nov 29|
Moderate 75 US AQI
|Monday, Nov 30|
Good 38 US AQI
|Tuesday, Dec 1|
Moderate 58 US AQI
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San Francisco’s air quality is generally rated “good,” meaning that the air poses little risk to health. In 2019, San Francisco averaged an annual PM2.5 level of 7.1 μg/m3, meeting the World Health Organization’s (WHO) guideline for annual exposure (< 10 μg/m3).
The ‘good’ air quality status in San Francisco can be attributed to the city’s coastal geography, meteorology, and sparse industrial activity.
Air pollution in San Francisco comes primarily from transportation emissions, such as from vehicles, planes, and ships.1 Wildfires, which are becoming increasingly common in the Bay Area, give way to drastic air pollution spikes, usually in the summer and fall.
Discounting the influence of wildfires, winter months are commonly more polluted than summer months as a result of increased heating and wood burning. In 2019, November, January and December were the most polluted months for PM2.5 respectively (14.5, 10.7, and 8.2 μg/m3). November’s high average was partially attributable to the Ranch fire, which burned more than 2,534 acres.2
In the last 3 years, 5 of the most destructive California wildfires were in relatively close proximity to San Francisco, greatly impacting air quality across the Bay Area.3 In November 2018, the Camp fire burned 153,336 acres and drove San Francisco’s AQI for the month up to 137 (“unhealthy for sensitive groups”). Air pollution levels in other Bay Area cities, such as San Jose and Oakland, experienced a similar rise.
Numerous other fires in 2018, including the Kincade Fire, Carr Fire, and Mendocino Complex Fire, further elevated San Francisco’s air pollution levels. The city’s annual PM2.5 average for this year was 12.6 μg/m3 (“moderate”), exceeding the WHO annual target for safe PM2.5 exposure, and raising the city's ranking to 49 of 723 for worst air pollution in the United States.
Wildfires in the Bay Area have been growing in size and frequency over the last two decades. The shift has coincided with rising temperatures and changing weather patterns, as a result of anthropogenic climate change. Environmental scientists expect the number burned acres per year to continue to rise over the coming years, presenting a growing challenge for Bay Area air quality. 4
Generally, air quality in San Francisco is best in the spring, as temperatures warm and forest undergrowth is still wet from the frequent rains in the winter months. March often experiences the cleanest monthly air quality of the year, as was the case in 2019.
While year-on-year air quality trends are fairly consistent, real-time air quality is subject to daily fluctuations based on weather events and emissions. Live air pollution data is therefore a valuable resource in understanding how to best protect one’s health and the health of loved ones. Refer to the top of this page for San Francisco’s forecast air quality data and real-time air quality data in order to better understand present conditions and necessary health advisories.
In recent years, air quality in the Bay Area has been highly contingent on the wildfire season. In 2019, for example, San Francisco experienced a 43.7% decrease in PM2.5 from the year prior, though this reduction is attributed largely to the reduction in severe wildfires and not from emission reductions from other sources. 2018 experienced severe wildfires, and thus experienced a 26% increase in PM2.5 from 2017.
On a larger scale, despite a growing population and economy, air pollution in the Bay Area has improved significantly in the last 30 years since the 1990 amendments to the Clean Air Act. Increasingly tight regulations against industrial activity and related emission sources are to credit. The Hunters Point and Potrero Hill power plants were closed in 2006 and 2010 respectively, while other industrial businesses have since moved out of the city. The effect has been a reduction in “unhealthy” air quality. Yet there has not been a significant increase in days classified as “good” (AQI 0-50).5 This is because pollution levels on average have decreased, while peaks into “moderate” air quality levels are still common. In recent years, roughly 20-25% of calendar days average “moderate” or worse air quality.
In order to further reduce San Francisco’s air quality index, a shift from fossil fuel dependence, such as gas-powered transport, to cleaner, more sustainable energy is needed. San Francisco currently aims to transition to 100% renewable electrical power by 2030, while shifting to 100% greenhouse gas-free transportation by 2040.6,7
Wildfires are a more difficult emission source to regulate, particularly in a warming climate. Prevention methods, such as creating fire lines and removing volatile forest undergrowth through low-intensity “prescribed fires,” offer ways to reduce the size and ecological impact of wildfires in the Bay Area. The California Department of Forestry and Fire Prevention (CAL FIRE) estimates that 8-10 million acres urgently require thinning and ‘prescribed burning’ in order to prevent mega-fires, or future disastrous wildfires.8 In coordination with the U.S. Forest Service, they aim to thin a million acres a year, an ambitious target.
Despite fewer power plants and industrial businesses as well as a growing mix of cleaner energy, San Francisco still experiences periods of unhealthy air quality. Primary factors for elevated pollution levels in the Bay Area include transportation emissions from cars, trucks, planes, and ships as well as seasonal wildfires.
While transportation emissions are a constant source of air pollution, wildfires are generally the reason for extreme air quality events, such as air quality in San Francisco being described as “unhealthy” or worse.
City-wide emissions are frequently trapped near the ground as a result of a weather event described as marine inversion. Marine inversions are temperature inversions created by a city’s proximity to an ocean or large body of water. In the case of San Francisco, waters from the Pacific ocean are cold and reduce ground temperatures in surrounding areas. These temperatures are often significantly colder than the winds moving over the region from inland locations.
By viewing an air pollution map of San Francisco and present wind directions, it’s possible to get a sense of where polluted air is coming from - either inland emission sources, such as wildfires, regular emissions as a result of transport, or trapped air pollution due to a marine inversion (polluted San Francisco air, with wind blowing from towards the coast).
San Francisco has achieved improving air quality over the last 30 years. These improvements have largely been driven by cleaner transportation options (such as a gradual transition towards electric and hybrid vehicles), tighter regulatory controls on industry, and increasingly stringent local and state regulations on emissions ranging from domestic wood burning to port activity.
Despite significant improvements, air quality in the San Francisco Bay Area has breached federal standards for 24-hour PM2.5 since 2017. This comes after meeting this standard for almost a decade from 2008 to 2017.
The recent increase in the number of unhealthy PM2.5 days in San Francisco is primarily attributable to a surge in wildfires. 2017 was a record-breaking year for burned acreage in California, quickly superseded by 2018 and then 2020. A growing population, congested roads, and new construction have also contribute to heightened ambient particle pollution in the Bay Area.
The City and County of San Francisco developed the Air Quality Element of the General Plan in order to improve air quality and achieve State and federal standards. The plan targets:
The Plan’s multi-pronged approach includes initiatives such as improving the accessibility and attractiveness of pedestrian/bike lanes, incentivizing electric vehicles, city planning for reduced traffic, and enforcement of over-polluting industries, among others.
Separately, the Bay Area and CAL FIRE are engaged in pre-emptive firefighting to reduce the severity of future wildfires, San Francisco’s leading cause for unhealthy PM2.5 days. Preemptive firefighting includes clearing fire lines and thinning forest underbrush through small, controlled “prescribed fires.”
California wildfires have become more frequent and severe in recent years. According to a study conducted by the Lamont Doherty Earth Observatory at Columbia University, climate change has doubled the risk of extreme fire conditions in California since 1970. During the same period, the amount of annual acreage burned has jumped eight-fold.
As wildfires rise in frequency and severity, so too does the threat of wildfire smoke. 2020 represented a historic year for both wildfires and unhealthy air pollution days.
The 2020 August Complex fire burned for more than 55 days, surpassing a million scorched acres and becoming the largest fire in California history.9 During this period, San Francisco air quality levels reached “unhealthy” or worse levels for more than 10 combined days.
When wildfires are burning, air quality can be fast changing, wavering from “good” to “unhealthy” based on wind and weather conditions. Follow San Francisco’s forecast air quality data at the top of this page to discover when wildfire smoke will clear. The IQAir forecast model employs machine learning to analyze millions of air quality data points along with current and forecast weather conditions to provide the most arcuate air quality predictions.
+ Article Resources
 San Francisco Planning Department - air quality element. (2020).
 Cal-Fire - Ranch Fire. (2020).
 Top 20 most destructive California wildfires. (2020).
 Ray S, Miller B, and Jones J. (2020, August 25). California’s new normal: How the climate crisis is fueling wildfires and changing life in the Golden State.
 Days with an EPA Air Quality Index Rating of "Good". (2020).
 SF Environment - Clean Fuels and Vehicles. (2020).
 SF Environment - Clean Fuels and Vehicles. (2020).
 Helvarg D. (2019, December 20). How will California prevent more mega-wildfire disasters?.
 Kaur H. (2020, October 6). California fire is now a 'gigafire,' a rare designation for a blaze that burns at least a million acres. CNN.
Data sources 5