Qualité de l’air à Castro Valley

How is air quality in Castro Valley, CA?

In a year, daily average air quality in Castro Valley ranges from “good” to “very unhealthy.” Air pollutants like PM2.5 and ozone are both attributable to spikes in daily air quality. In the three-year monitoring period between 2016 and 2018, both pollutants had caused “very unhealthy” short-term air quality.¹ Despite such swings, the vast majority of days do meet the US Environmental Protection Agency (EPA) standard for “good” air quality. In 2019, Castro Valley averaged an air quality index (AQI) score of 30, well below the 50 AQI threshold for healthy air.

The American Lung Association (ALA) releases an annual report card grading US cities for their ability to meet US EPA pollution measures for PM2.5 and ozone. Alameda County, of which Castro Valley is a part, passed standards for annual PM2.5, but failed to meet standards for both short-term PM2.5 and short-term ozone. Alameda’s “F” grade for 24-hour pollution was given due to the County’s excess of unhealthy days over the federal allowance of 3.2 days per year. During the 2016 to 2018 monitoring period, Alameda averaged 8.8 unhealthy ozone days and 11.2 unhealthy PM2.5 days.

In the United States, Alameda County ranks highly for poor air quality. In the same 2016 to 2018 monitoring period, Alameda ranked 3rd for high PM2.5 days out of 216 metropolitan areas in the United States, and 8th for high ozone days out of 229 metropolitan areas.

While the Bay Area has implemented a range of regulatory policies aimed at every common emission source, short-term PM2.5 and ozone are difficult to tackle, particularly in a warming climate as a result of anthropogenic global warming. This is because hotter temperatures prolong and exacerbate both the ozone season (as ozone requires heat to form in the atmosphere) and wildfire season.

Follow live air quality data in Castro Valley in order to stay aware of pollution peaks. Taking the recommended health recommendations during such periods of high pollution helps to limit exposure and safeguard health. When the AQI in Castro Valley exceeds 50 (“good”), the air may pose risks to health, particularly to those vulnerable to pollution such as children, the elderly, and those with heart and lung disease.

What is Castro Valley doing to improve air quality?

Air quality in Castro Valley has improved since the first federal regulations were placed on air pollution emissions with the Clean Air Act of 1970. The later 1990 amendments to the Clean Air Act paved the way for increased air quality monitoring, emission control, and enforcement, proving to be the most impactful of the federal regulations for healthy air.² It is estimated that in the last 50 years (from 1970 through 2020), these amendments alone have prevented as many as 237,000 deaths, while improving the health of countless more.

On a state level, California has been most effective at tackling air pollution through transportation regulations on both personal and commercial (diesel) motor vehicles. California state, in collaboration with the federal EPA, has funded a grant program for retrofitting older diesel engines with cleaner burning engines.³ California state made a commitment in 2020 to only sell zero-emission vehicles by 2035.⁴ Moving towards more electric and hybrid vehicles offers an opportunity to greatly reduce emissions, as motor-vehicles contribute up to 60 percent of an American city’s pollution mix.

On a local level, Castro Valley is seeking to grow public transportation and sidewalk space as well as add more electric vehicle charging stations and grants for electric vehicles to promote cleaner transportation options.⁵

Despite decades of progress, Alameda County has seen a trend of worsening particle pollution since 2017. Record-breaking wildfire seasons are in part to blame. 2017 was a historic wildfire season, immediately bested by 2018 and then 2020. Many of the fires burning in California were in the Bay Area region. Particularly devastating fires in recent years have included the Kincade Fire, Carr Fire, Mendocino Complex Fire, and 2020 lightning complex fires.

Regulatory rollbacks made by the Trump administration’s EPA have been another factor. In the three years from 2016 to 2019, 16 regulatory rollbacks on air pollution emissions were completed, while many others are in progress.⁶ These rollbacks have included attacks on emission standards, oversight, and enforcement, all contributing to higher emissions and air pollution levels.

In order to further drive down air pollution levels in Castro Valley, progress must be made in further reducing emissions for vehicles and industry. Climate action, burn bans, and prescribed fires, meanwhile, offer opportunities to reduce the frequency and severity of wildfire seasons.

Is the Castro Valley air safe to breathe today?

Cities are often categorized for clean or unhealthy air based on daily emissions. Such generalizations, however, often fail to describe current conditions, as air quality is incredibly fast-changing and dynamic.

Weather plays a near equal role to emissions in determining a city’s air quality. This is because weather conditions like wind, rain, and temperature all affect pollution dispersion. Based on the combination of weather conditions, emissions can either accumulate and exacerbate air pollution levels or scatter and lower air pollution levels.

In Castro Valley, AQI levels benefit from sea breezes that blow clean air inland from the Pacific Ocean or San Francisco Bay. Sea breezes generally carry clean air to the city. The eastern hills of Castro Valley, including mountains in the Garrin, Las Trampas, and Reinhardt Redwood Regional Parks, however, can trap city air pollution, preventing it from dispersing eastward. This effect can be exacerbated during marine inversions, in which ground level air chilled by the ocean becomes trapped under warmer air layers above. During marine inversions, emissions accumulate until conditions change.

Even within a single day, air quality levels can vary, as a result of pollution events and changing weather. Follow live and forecast air quality data in Castro Valley with the IQAir website and mobile app.

Where does Castro Valley air pollution come from?

Air pollution sources in Castro Valley include motor vehicles, fossil-fuel based energy production, domestic wood burning, transboundary pollution from nearby cities, and wildfires as the leading natural cause.

Daily emissions typically result in relatively healthy air quality, as annual averages in Castro Valley remain in the US AQI “good” category. Air pollution from wildfires and winter wood burning is often the reason particle pollution levels in Castro Valley become unhealthy.

In recent years, the influence of wildfire smoke on air quality has grown in direct correlation to more frequent and severe fires. Fires started in 2020 as a result of a ‘lightning siege’ that caused Castro Valley to rank for the most polluted cities in California as air quality levels reached “very unhealthy” levels.

When wildfires strike, and other pollution events occur, many locations across the Bay Area share similar air quality ratings. Slight variations in pollution levels highlight emission trends produced by each Bay Area city as well as a city’s proximity to wildfires. While Castro Valley averaged a PM2.5 concentration of 7.1 μg/m³ in 2019, with a monthly high of 15.8 μg/m³ in November, nearby cities averaged:

• Fremont air quality: 7.5 μg/m³ in 2019. Monthly high in November: 19.1 μg/m³ .
• Berkeley air quality: 7.1 μg/m³ in 2019. Monthly high in November: 14.8 μg/m³ .
• San Francisco air quality: 7.1 μg/m³ in 2019. Monthly high in November: 14.5 μg/m³ .
• Oakland air quality: 7 μg/m³ in 2019. Monthly high in November: 15.5 μg/m³ .
• Walnut Creek air quality: 6.6 μg/m³ in 2019. Monthly high in November: 14.2 μg/m³ .
• San Jose air quality: 6.4 μg/m³ in 2019. Monthly high in November: 15.9 μg/m³ .

When will smoke in Castro Valley clear?

California’s wildfire season is getting worse. While wildfires play an important role in our planet's ecosystems, the rise in wildfires in recent decades have been attributed by scientists to anthropogenic climate change.⁷ The rise in greenhouse gases in our atmosphere has contributed to warmer temperatures, earlier snowmelt, increased evaporation, greater water loss in plants, drier soils, and an excess of forest undergrowth. Combined with a rising population, acts of human negligence (such as poorly smothered cigarettes and campfires as well as fireworks or explosive devices used in gender reveal parties) have helped to cause an increase in fires that rage hotter and longer than decades past.

Wildfires in 2020 blew past previous state records set in 2017 and 2018, causing far-reaching smoke in the Bay Area, greatly affecting air quality in Castro Valley. In 2020, the Lightning Complex Fires in Northern California caused Castro Valley to experience several days of “very unhealthy” air quality, some of the worst air quality the city has ever experienced.

Sea breezes and normal temperature conditions help to moderate the effect of wildfire smoke in Castro Valley. Discover active fires burning in the region, and the flow of emissions based on wind, by using the IQAir air quality map. Forecast air quality data in Castro Valley can be discovered at the top of this page, under the “Forecast” header. Use the forecast to see how weather conditions may help alleviate Bay Area smoke.

+ Article Resources

[1] American Lung Association. (2020). State of the Air – 2020.
[2] United States Environmental Protection Agency (EPA). (2020). Benefits and costs of the Clean Air Act 1990-2020, the second prospective study.
[3] EPA. (2020). Diesel Emissions Reduction Act (DERA) funding.
[4] Valdes-Dapena P. (2020, October 3). California's mandate to sell only zero-emissions vehicles by 2035 isn't as crazy as critics think. CNN.
[5] Swan R. (2019, December 7). With new grant program, Bay Area spreads electric cars to low-income drivers. San Francisco Chronicle.
[6] Popovich N, et al. (2019, December 21). 95 environmental rules being rolled back under Trump. The New York Times.
[7] Union of Concerned Scientists. (2020, March 11). The connection between climate change and wildfires.