Qualité de l’air à Fremont

How is the air quality in Fremont CA?

Fremont’s annual air quality index score meets the US Environmental Protection Agency (EPA) standard for “good,” with a US AQI of 31. Fremont’s “good” air quality status is an oversimplification, smoothing over unhealthy air quality days with its typically clean air. But the day-to-day situation shows a different story. Importantly, the WHO states that no level of air pollution has been shown to be free of health impacts.¹

Alameda County, of which Fremont is a part, received an “F”, or failing grade, for both PM2.5 and ozone measures for short-term air pollution.² The US EPA allows only 3.2 unhealthy pollution days for each pollutant. In the 2016-2018 monitoring period, there were an average of 8.8 unhealthy ozone days and 11.2 unhealthy PM2.5 days per year.

Even in the short term, air pollution spikes can cause adverse health effects, particularly in populations deemed “sensitive,” such as those with pre-existing heart and lung conditions, children, and the elderly. Alameda County has 133,767 residents with asthma, 59,858 with COPD, 86,118 with cardiovascular disease, 230,510 residents over the age of 65, and 342,510 children under the age of 18, all who qualify as “sensitive.”

Follow live air quality data for Fremont at the top of this page. When Fremont’s air quality index score is under 50, air is deemed “good” and poses little to no risk to human health. When Fremont’s AQI levels exceed 100, “unhealthy for sensitive groups,” and precautions, such as following the advised health recommendations, should be taken to reduce pollution exposure.

Why is Fremont air quality so bad?

Air pollution in Fremont is on the rise despite a growing shift towards cleaner energy, more stringent local and state regulations, and a greater share of electric vehicles on the road. The reason has roots in the changing climate, as warming temperatures are linked to increased ozone and PM2.5 pollution in the area.

Ozone formation is dependent on sunlight and temperatures over 84 degrees in addition to the presence of ambient precursor pollutants, nitrogen dioxide (NO₂), and volatile organic compounds (VOCs). As temperatures rise, the ozone season becomes longer and elevated ozone levels become more common.

Data collected by the American Lung Association uses a weighted average across three years to indicate the average number of unhealthy ozone days. During the 2011-2013 and 2012-2014 monitoring periods, Alameda county averaged 5.2 and 4.8 unhealthy ozone days a year, respectively. These measurements rose significantly in the 2014-2016 and 2015-2017 monitoring periods to an average 10.7 and 10.8 unhealthy ozone days a year.

Fine particulate matter, or PM2.5 pollution, also appears to be on the rise in direct correlation with recent severe wildfire seasons. Wildfire smoke has a direct impact on the number of unhealthy PM2.5 days the city experiences each year.

In the 2014-2016 monitoring period, a relatively mild period for wildfires, Alameda county met federal attainment levels for short-term PM2.5, with an average of 2 unhealthy PM2.5 days a year. In the 2015-2017 and 2016-2018 monitoring periods, however, the county failed to meet federal attainment, with an average of 5.5 and 11.2 unhealthy PM2.5 days, respectively.

Is today a Spare the Air day in Fremont CA?

The Bay Area Air Quality Management District (BAAQMD) issues Spare the Air alerts when air quality in Fremont, California is forecast to be unhealthy.³ The alerts signal that residents should take action to protect their health by following recommended guidelines and reduce their emissions, taking part in the collective effort to help drive down pollution levels.

Most of the time, Spare the Air alerts signal high short-term PM2.5 or ozone pollution. Alerts for particle pollution are more common in the late summer, fall, and winter as a result of wildfires and wood burning, while alerts for ozone are more common in the summer when high temperatures (greater than 84 degrees) are ideal for ozone formation in the atmosphere.

Spare the Air alerts use the US air quality index (AQI) system as parameters of “unhealthy” air. Each pollutant has both a measured concentration value and translated AQI value. “Unhealthy” air is deemed as any pollutant with an AQI over 100. For PM2.5, this is a concentration over 35.4 μg/m³, and for ozone this is a concentration over 70 ppb.

Since warm temperatures are required for ozone to form in the atmosphere, Fremont’s ozone season usually runs from April to October, with roughly a dozen days annually that meet ideal requirements.⁴ Climate change, which has already caused increases in summer temperatures in California by 2.5 degrees in the past 50 years, is expected to accelerate ozone formation, increasing concentration levels and prolonging the ozone season.⁵ When ozone is the cause for a Spare the Air alert, residents may experience lung irritation, coughing, and difficulty breathing. Prolonged exposure can contribute to more acute health outcomes such as respiratory infections, permanent lung damage, cancer, and early death.

When temperatures cool during the fall and winter, Fremont’s air quality is more likely to register Spare the Air alerts for PM2.5 pollution. November through February typically registers the highest PM2.5 levels – up to 2 times the levels of the summer. Wood burning for domestic heating and enjoyment is a major contributor, as is a pollution-trapping weather event known as a temperature inversion.

Wildfires in the late summer and early fall are another source of PM2.5 pollution, which is becoming increasingly significant with climate change. While only temporary, wildfires can have a dramatic effect on air quality and cause long stretches of Spare the Air alerts in Fremont.

Record wildfires burning in 2020 caused a record stretch of Spare the Air alerts in Fremont, California. The previous record of 14 straight days of alerts was set in 2018 as a result of the Camp Fires.⁶

A Spare the Air alert is in place anytime air quality reaches “orange” air quality with an AQI above 100. When an alert is in place, follow Fremont’s live air quality data and forecast data at the top of this page, and take the recommended health precautions. If possible, play a role in reducing city-wide emissions by driving less and avoiding wood burning or BBQing.

How close are the fires to Fremont California?

Record California wildfires, heat, and smog have perpetually generated news headlines in recent years as new wildfire seasons top recently set records. This trend is not specific to California but has been observed all over the world. Scientists attribute this phenomenon to anthropogenic, or human-caused, climate change.

In the last 50 years, the number of acres burned by California wildfires has increased eightfold, while summer temperatures have risen by 2.5 degrees. The rising temperatures have caused snowmelt to occur earlier, extending the long dry summer. Eight of California’s 20 largest fires in recorded history have occurred in since 2017. The August Complex Fire of 2020, burning southeast of Redding in the Mendocino National Forest, is now the largest recorded wildfire in California, surpassing the 2018 Mendocino Complex Fire in the same area.

While wildfires are understood as an environmental crisis, they are also a public health crisis. Breathing wildfire smoke is linked to increased hospital visits from respiratory irritation and difficulty breathing to more serious effects like reduced lung function, inflammation, bronchitis, exacerbation of heart and lung disease, heart failure, and even early death. Children, the elderly, and those with pre-existing conditions are at greater risk for experiencing adverse health effects.

The IQAir map locates fires using NASA's Fire Information for Resource Management System (FIRMS) satellite observations and shows how wind patterns and weather affect the transport of emissions across the area. Use the map to see which fires are burning where, and how air quality in Fremont is currently being affected.

Does Fremont have better air quality than other cities in the Bay Area?

In 2019, Fremont suffered worse air quality than its Bay Area neighbors. This rating, however, was of no direct fault of this city itself but rather the result of nearby wildfires burning in November.

The majority of Fremont’s monthly averages in 2019 were consistently lower than neighbors such as Berkeley, San Francisco, and Oakland, though not as low as nearby San Jose and Walnut Creek.

November wildfires, including the Burris fire in Mendocino and the Kincade Fire in Sonoma County, contributed to elevated PM2.5 levels throughout the Bay Area in 2019 but particularly in Fremont and Walnut Creek, which are relatively closer to the source of these fires.

Overall, Fremont tends to experience air quality closely in line with the rest of the Bay Area. As wildfires play an increasingly important role in Bay Area pollution, proximity to fires is likely to remain a determinant for city rankings.

Use the Fremont air quality map to compare air quality across the Bay Area in real time, at a glance. Since air quality is dynamic, depending heavily on real-time emissions and weather conditions, evaluating air quality comparatively is likely to vary.

+ Article Resources

[1] World Health Organization. (2020). Air quality guidelines – global update 2005.
[2] American Lung Association. (2020). State of the Air – 2020.
[3] Spare the Air. (2020). What is Spare the Air? Bay Area Air Quality Management District.
[4] Current Results. (2020). San Francisco temperatures: Averages by month.
[5] 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. East Bay Times.
[6] Glover J. (2020, September 3). Spare the Air extended through Saturday as poor air quality, hazy conditions continue in Bay Area. ABC 7 News.