Air quality in Santa Rosa

How is the air quality in Santa Rosa, CA?

Santa Rosa is a city in Sonoma County considered to be one of the world capitals of wine production. Santa Rosa air quality index (AQI) readings are generally considered to be “good” according the US air quality index (AQI) scale.

Santa Rosa is relatively remote in comparison to nearby major metropolitan areas, including the San Francisco Bay Area. Santa Rosa also has a comparatively small population of about 177,000 (about 328,000 in the greater Santa Rosa area) in relation to much larger Northern California cities like San Francisco and Oakland. As a result, Santa Rosa generally does not experience a high volume of air pollution from industry and vehicle traffic that is typical of the San Francisco Bay Area.¹

In 2019, Santa Rosa air quality averaged an annual concentration of fine particles (PM2.5, or particulate matter smaller than 2.5 microns in diameter) of 6.8 µg/m³ (equivalent to a US AQI measurement of 28). This is well below the World Health Organization’s (WHO) annual mean threshold of 10 µg/m³ and well within the “good” range of US AQI measurements. According to the US AQI developed by the Environmental Protection Agency (EPA), any AQI measurement between 0 and 50 is considered “good” and is defined as posing little to no risk to any individuals in the general population.

However, the WHO, a leading global health organization, along with researchers from The Lancet, have stated that no level of air pollution is ultimately safe.² Even lower concentrations of air pollution, especially PM2.5 particles that are small enough to be breathed into the lung and penetrate into the bloodstream, have been linked to long-term health effects such as lung disease, heart disease, and premature death.

The Santa Rosa AQI has also been subject to drastic spikes in concentrations of dangerous air pollutants like PM2.5 due to the increasing prevalence of wildfires in California and, in particular, around the greater San Francisco Bay Area and Northern California. In the fall of 2019, the air quality index in Santa Rosa experienced noticeable increases, in some cases more than doubling from the monthly average of 6.8 µg/m³ to as high as 12.6 µg/m³ (US AQI measurement of 52, “moderate”) as a result of several major wildfires in the Bay Area and beyond, including:

• Getty fire: burned 745 acres in a dense area of western Los Angeles near Brentwood, CA, resulting in the displacement of thousands of residents and the destruction or damage of 25 residences³
• Kincade fire: burned 77,758 acres in Sonoma County and prompted the evacuation of thousands in the area, including a significant part of the population of Santa Rosa, and which was the biggest fire in Sonoma County history at the time⁴

Although the increases in PM2.5 from wildfires in 2019 did not appear to make a significant impact on the overall AQI for the city during the 2019 monitoring period, long-term air quality averages can often smooth over the dangerous, long-lasting health impacts of brief but extreme fluctuations in air quality.

Air quality can also change quickly even in a matter of hours or days due to weather conditions as well as events like increased commuter traffic or wildfires. Follow our Santa Rosa air quality map and see the Santa Rosa air quality forecast here on the IQAir website and on the IQAir AirVisual mobile app. When the Santa Rosa AQI rises higher than 50 (“good”), air pollution levels may increase the risk of health effects in vulnerable populations. These populations include the elderly, young children, and people with respiratory or cardiovascular disease.

How does Santa Rosa air quality compare with the air quality in Rohnert Park?

Air quality in Rohnert Park, a suburb in the greater Santa Rosa area with a population of around 43,000, experiences similar air quality to Santa Rosa. Like Santa Rosa, air quality in Rohnert Park is generally “good”, with a 2019 annual average PM2.5 concentration of 8.5 µg/m³ (US AQI measurement of 35, slightly higher than Santa Rosa but still well below the WHO’s annual fine particle concentration average threshold of 10 µg/m³ and within the “good” range of the US AQI scale).

Like Santa Rosa, Rohnert Park air quality has also been greatly impacted by increasingly severe wildfires in the Bay Area and the state of California. Air quality throughout California has generally improved in the past two decades.⁵ However, historic wildfire seasons in the Bay Area during 2017, 2018, and 2020, including the 2020 Lightning Complex fires and the Kincade Fire, Carr Fire, and Mendocino Complex fires in previous years, have exposed both Santa Rosa and Rohnert Park to weeks of hazardous air quality.

In 2019, Rohnert Park saw many months of relatively good air quality well below the WHO and EPA thresholds for acceptable air quality. However, in the last few months of 2019, wildfires burning throughout the Bay Area resulted in air pollution concentrations nearly double the average air quality measurements in Rohnert Park throughout the year:

• October: 11.6 µg/m³ (US AQI: 48)
• November: 15.2 µg/m³ (US AQI: 58)
• December: 12.1 µg/m³ (US AQI: 51)

Although these measurements may not seem high at first glance, the major increase from the monthly average of 8.5 due to wildfire smoke resulted from numerous days of “unhealthy” air quality (US AQI measurements between 151-200) that inflated each month’s average despite mostly good air quality during periods with no wildfires.⁶

Where is the highest rate of air pollution in Santa Rosa?

Major daily sources of air pollution in Santa Rosa include:

• motor vehicles, especially commercial transportation and maintenance vehicles that service the region’s wine industry and travel along Highway 101 in the center of town
• transboundary pollution that can blow in from the dense San Francisco Bay Area nearby
• domestic wood burning, especially during the colder months from October to December

Vehicle traffic is not typically heavy within Santa Rosa, and vehicle emissions generally do not build up to high enough concentrations to reach beyond “good” on the AQI scale. However, wildfires in or near Santa Rosa and Sonoma County result in high rates of air pollution that do not reflect the typical patterns of air quality in Santa Rosa. Nonetheless, the Lightning Complex fires caused Santa Rosa to rank as one of the most polluted cities in California for numerous days in August and September of 2020, with several days experiencing air quality well into the 200s on the AQI scale (“very unhealthy”) and posing a major health threat to everyone in Santa Rosa.

During wildfires in the San Francisco Bay Area region, many cities in the greater Bay Area, including Santa Rosa, experience similar levels of air pollution, with some variation based on specific emission sources and geography within each city. Average PM2.5 concentrations in Santa Rosa stood at 6.8 μg/m³ during 2019 and reached a yearly high in November of 12.6 μg/m³, while nearby cities averaged:

• Petaluma air quality: 6.7 μg/m³ for 2019 (US AQI: 28), with highest monthly average in November at 12.4 μg/m³ (US AQI: 52)
• San Rafael air quality: 5.7 μg/m³ (US AQI: 24) for 2019, with highest monthly average in November at 11.5 μg/m³ (US AQI: 48).
• Richmond air quality: 6.5 μg/m³ (US AQI: 27) for 2019, with highest monthly average in November at 14.6 μg/m³ (US AQI: 56).
• Vallejo air quality: 7.7 μg/m³ (US AQI: 32) for 2019, with highest monthly average in November at 17.0 μg/m³ (US AQI: 61).
• San Francisco air quality: 7.1 μg/m³ (US AQI: 30) for 2019, with highest monthly average in November at 14.5 μg/m³ (US AQI: 56).
• Oakland air quality: 7 μg/m³ (US AQI: 29) for 2019, with highest monthly average in November at 15.5 μg/m³ (US AQI: 58).

What does weather have to do with Santa Rosa air quality?

Along with sources of air pollution, especially traffic from Santa Rosa’s major highways like the Redwood Highway 101, weather also plays a major role in Santa Rosa air quality. In general, weather conditions like temperature, wind, and rain all influence how air pollution behaves. During windy days, particulate pollution can be dispersed widely, reducing the concentration of air pollution in the city. During rainy days, air pollutants can be absorbed by raindrops, helping reduce air pollution concentrations in the lower atmosphere.⁷

Because of Santa Rosa’s close proximity to large bodies of water, including the San Pablo Bay, the San Francisco Bay, and the Pacific Ocean as well as its location in Northern California, Santa Rosa experiences relatively mild temperatures. Daily highs typically reach 84 degrees Fahrenheit (°F) during the summer and daily lows can reach 38 during winter months. As a result, Santa Rosa does not experience much ozone (O₃) pollution. Ozone, which is formed when air pollution in the lower atmosphere reacts with heat from sunlight, typically reaches dangerous concentrations at 84°F and above.

However, Santa Rosa air pollution can also be impacted by cooler temperatures. Typically, Santa Rosa’s high daytime temperatures range from 60-80°F and then drop at night to between 40-50°F. In general, pollutants tend to accumulate during the day when human activity increases – vehicle traffic from streets and highways, especially, generates high concentrations of PM2.5 and gaseous pollutants like sulphur dioxide (SO₂) and nitrogen dioxide (NO₂). Then, as the temperature drops at night and warm air begins to rise higher into the atmosphere, cooler, less dense air near the ground becomes trapped by warmer air at higher elevations, trapping air pollution with it.

This is known as a temperature inversion – warm layers of air that act like a lid, restricting cool, ground-level air from dispersing and causing air pollution to build up to dangerously high concentrations, especially during wildfires that continuously generate PM2.5 and gases. This effect can be exacerbated as warm air blows over the Estero Lowlands and small series of hills to the west of Santa Rosa and traps cool air in the Santa Rosa Plain in which the city is located. Due to the influence of the offshore breeze from the nearby Pacific Ocean and San Pablo Bay, ground-level air cooled by marine breezes can also lead to marine inversions, although marine breezes can also sometimes help disperse pollutants throughout the day.⁸

How does Santa Rosa air quality compare with Sonoma County air quality?

The air quality in Sonoma County, of which Santa Rosa is the county seat, is relatively good in comparison to the air quality in California’s other major cities.

The State of the Air report by the American Lung Association assigns major cities and counties a letter grade for ozone and 24-hour particle pollution (that is, how many individual days out of a given year experienced particle pollution in high concentrations) as well as annual particle pollution (assessed by the overall average of particle pollution experienced across the entire year). The State of the Air report assigned the following letter grades to Sonoma County during the 2016-2018 measurement period:⁹

• Ozone: B, with an average concentration of 1 µg/m³ during the 2016-2018 measurement period. Overall, Sonoma County only experienced an average concentration of 0.3 µg/m³ for ozone pollution, with 3 µg/m³ being the threshold for a failing grade of “F”.


• 24-hour particle pollution: F, with an average concentration of 4 days of air pollution in the “orange” range, 11 days in the “red” (unhealthy) range, and 2 days in the “purple” (very unhealthy) range for a total average of 8.2 days throughout the year experiencing high concentrations of particle pollution during a 24-hour period during 2016-2018.


• Annual particle pollution: PASS, with only an average of 7 µg/m³ throughout the 2016-2018 period experiencing levels of particle pollution that reached high concentration.

Ozone and annual particle pollution in Sonoma County have improved over the years, with ozone down from its peak of 9.7 unhealthy ozone days during the 1997-1999 monitoring period and annual particle pollution down from a peak average of 10.5 µg/m³ during the 2000-2002 monitoring period. However, 24-hour particle pollution saw an extreme spike from an all-time low in 2014-2016 of 0 to 1.8 during 2015-2017 and to 8.2 during 2016-2018.

This increase is attributable to a series of record-breaking wildfires that struck Santa Rosa during these periods. In 2020 Sonoma County and Santa Rosa again experienced dangerously high levels of air pollution from a series of wildfires in Northern California called the Lightning Complex Fires, which sent plumes of wildfire smoke throughout the Bay Area and greater Northern California for hundreds of miles and caused air quality in Sonoma County and Santa Rosa to reach emergency levels for days at a time.

+ Article Resources

[1] United States Census Bureau. (2020). QuickFacts: Santa Rosa city, California.
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DOI: 10.1016/S2542-5196(19)30262-1
[3] Los Angeles Fire Department. (2019). Getty Fire.
[4] Kovner G. (2019, October 30). Kincade fire burns into history as Sonoma County’s largest blaze. The Press Democrat.
[5] Kaiser Health News. (2019, November 6). California air quality: Mapping the progress. US News & World Report.
[6] Espinoza M. (2019, October 25). Sonoma County public health officials issue poor air quality warning due to Kincade fire. The Press Democrat.
[7] Shukla JB, et al. (2008). Effect of rain on removal of a gaseous pollutant and two different particulate matters from the atmosphere of a city.
DOI: 10.1016/j.mcm.2007.10.016
[8] The City of Santa Rosa. (2012). Environmental impact report: North Santa Rosa Station area.
[9] American Lung Association. (2020). State of the Air – Report.