California's Air Quality: Is The Golden State Polluted?

California has some of the worst pollution levels in the United States, with over 90% of its residents breathing in unhealthy levels of air pollutants. The state's air quality has been a concern since 1943 when residents first complained about the side effects of smog. While California has made significant progress in improving its air quality, particularly through aggressive emissions policies, racial disparities persist, with low-income communities of colour still breathing the dirtiest air. The state's air pollution is caused by a variety of factors, including transportation emissions, industrial processes, and wildfires, which have become increasingly frequent and severe.

Wildfires and air pollution

Wildfires are a significant contributor to California's air pollution. The state has seen a rise in the number of annual burned acres, with 2019 being a record-breaking year. More than 3.2 million acres burned in California that year, and the trend continued in 2020, which was a record-setting year for wildfires in the Pacific West region.

Wildfires emit substantial amounts of carbon and air pollutants, with severe environmental and health consequences. The smoke released during these fires contains toxic substances, including carbon monoxide and benzene, a known carcinogen. The tiny particles of soot in the smoke are considered particularly hazardous as they can enter airways, lodge in lungs, and trigger asthma or heart attacks. The impact of wildfire smoke on air quality can be significant even in urban areas far from the flames, as smoke can travel long distances. For example, the January 2025 wildfires in Los Angeles, fuelled by strong Santa Ana winds, dry soil, and vegetation, led to a dramatic spike in fire intensity as measured by the Fire Radiative Power (FRP). This resulted in enhanced levels of PM2.5, a type of fine particulate matter, in the atmosphere.

The frequency and intensity of wildfires in California are influenced by climate change, creating a vicious cycle. As global temperatures rise, wildfires become more frequent and intense, releasing greenhouse gases that further contribute to warmer and drier conditions. This, in turn, ignites more fires, worsening the overall climate.

To address the impact of wildfires on air quality, local air quality districts in California send out warnings when wildfires spread smoke, and organisations like CAMS (Copernicus Atmospheric Monitoring Service) monitor wildfire emissions and their potential air quality impacts. Despite these efforts, wildfire smoke may be negating some of California's progress in improving air quality.

Air quality in Los Angeles

Los Angeles, California, is notorious for its smog, a combination of particle and ozone pollution. The city's air quality averages a US Air Quality Index (AQI) rating of "moderate", with monthly averages in 2019 varying from AQI 32 ("good") in February to AQI 64 ("moderate") in November. Despite these seemingly optimistic ratings, Los Angeles's air pollution is among the worst in the United States, particularly for PM2.5 and ozone.

PM2.5, or airborne particulate matter measuring up to 2.5 microns in size, is widely regarded as one of the most harmful pollutants to human health. Exposure to PM2.5 has been linked to health effects such as heart disease, respiratory illness, and premature death. The greater Los Angeles county contains 9 of the 15 most polluted cities in the United States, according to the 2019 World Air Quality Report.

Ozone, a gas pollutant formed when sunlight reacts with nitrogen oxides and organic substances, is also a significant contributor to Los Angeles's poor air quality. Vehicle exhaust is a leading source of ozone pollution, as it contains both the nitrogen oxides and reactive organic substances needed to form ozone. Like PM2.5, ozone can cause a range of health issues, from respiratory infections and inflammation to premature death. Together, PM2.5 and ozone create the smog that Los Angeles is often associated with.

The summer months of June, July, and August tend to be more polluted than other months due to drier conditions, less rainfall, higher temperatures, and a higher frequency of wind-blown dust and wildfires fanned by the Santa Ana winds. Wildfires have a significant impact on the city's air quality, and the long-term trend is for them to increase in frequency as temperatures rise and droughts lengthen. However, the COVID-19 lockdown measures in March 2020 resulted in Los Angeles experiencing an 18-day stretch of exceptionally clean air, with PM2.5 levels averaging 5.6 μg/m3 (US AQI 23).

While Los Angeles's air quality has improved over the last few decades due to emissions-reducing policies, racial disparities persist, with low-income communities of color still breathing the dirtiest air. Overall, Los Angeles's air pollution continues to pose a significant risk to public health, with associated health impacts evident in the numbers.

Reducing air pollution

California has been battling air pollution for decades. In 1943, residents complained that smog was causing side effects such as burning lungs, irritated eyes, coughing, and nausea. While the state has made significant progress since then, with residents breathing much cleaner air today than they did 25 years ago, California still has a long way to go in addressing its air quality issues.

Transportation Emissions:

California's air pollution is largely attributed to transportation emissions from personal and commercial motor vehicles. To tackle this, many Californian cities are encouraging residents to transition to electric vehicles by offering tax breaks and expanding the network of electric vehicle (EV) charging stations. Cities are also investing in public transportation infrastructure, making it a more attractive option for residents. Additionally, California has implemented aggressive emissions policies, such as the Tier 3 vehicle and fuel standards, which aim to reduce emissions from motor vehicles by 10 to 30 percent by 2030.

Industrial Sources:

Air pollutants from various industrial processes also impact the health of Californians. The EPA has played a crucial role in reducing toxic emissions from these sources by setting stringent emission standards and regulating hazardous air pollutants from large industrial facilities. Since 1990, the EPA has targeted over 174 categories of major industrial sources, including chemical plants, oil refineries, and steel mills.

Wildfires:

Wildfires are another significant contributor to California's air pollution, especially in recent years. While this is a challenging issue to address, preventative measures and effective responses to wildfires can help mitigate their impact on air quality.

Individual Actions:

Individuals can also play a role in reducing air pollution. Simple steps such as walking or biking instead of driving, limiting vehicle idling, and transitioning to electric or hand-powered lawn equipment can make a collective impact. Additionally, energy conservation at home, such as using energy-efficient appliances, reducing electricity consumption, and opting for natural substitutes for toxic chemicals, can contribute to cleaner air.

Policy and Planning:

Addressing air pollution requires systemic changes. Policies that accelerate the adoption of zero-emission vehicles, especially in overburdened communities, are crucial. Additionally, urban planning that distributes highways and industrial areas more evenly can help reduce the disproportionate impact of air pollution on low-income communities of color.

Health impact of air pollution

Air pollution is a mix of hazardous substances from both human-made and natural sources. It is a major threat to global health and prosperity and is responsible for more than 6.5 million deaths each year globally. In California, over 90% of residents breathe unhealthy levels of one or more air pollutants during some part of the year.

The main pathway of exposure from air pollution is through the respiratory tract. Breathing in these pollutants leads to inflammation, oxidative stress, immunosuppression, and mutagenicity in cells throughout the body, impacting the lungs, heart, and brain, among other organs, and ultimately leading to disease. Almost every organ in the body can be impacted by air pollution. Due to their small size, some air pollutants can penetrate into the bloodstream via the lungs and circulate throughout the entire body, leading to systemic inflammation and carcinogenicity.

Fine particulate matter (PM2.5) is an especially important source of health risks. These very small particles can penetrate deep into the lungs, enter the bloodstream, and travel to organs, causing systemic damage to tissues and cells. Exposure to high levels of PM2.5 can lead to reduced lung function, respiratory infections, and aggravated asthma from short-term exposure. Long-term or chronic exposure to fine particulate matter increases a person's risk for diseases with a longer onset, like some noncommunicable diseases, including stroke, heart disease, chronic obstructive pulmonary disease, and cancer. Air pollution is also associated with diabetes and neurological development in children. Maternal exposure to air pollution is associated with adverse birth outcomes, such as low birth weight, pre-term birth, and small for gestational age births.

In California, emissions from light-duty vehicles, like cars, are the main sources of exposure, although contributions from heavy-duty vehicles, such as port drayage trucks, have a higher impact on overburdened communities. Historically, racist housing policies, including redlining, have forced communities of color to live closer to highways and ports than predominantly white communities, and subsequently to breathe higher levels of air pollution. While California has dramatically improved its air quality over the past few decades, racial disparities persist, with low-income communities of color still breathing the dirtiest air.

Racial disparities in air quality

California has been battling air pollution since 1943 when residents first complained about the side effects of smog. In 1967, the state legislatures passed the Mulford-Carrell Air Resources Act, which established the California Air Resources Board (CARB). Since then, the state has been actively working to improve its air quality.

Despite the improvements, racial disparities persist in the state's air quality. A recent study found that while California's aggressive emissions policies have reduced residents' exposure to PM2.5 pollution from cars, trucks, and other vehicles by 65% since 2000, low-income communities of color still breathe the dirtiest air. Hispanics and Black Californians have seen the largest reductions in PM2.5 pollution, but they continue to be the groups most exposed to vehicle pollution.

Historically, racist housing policies, including redlining, have forced communities of color to live closer to highways and ports, leading to higher levels of air pollution. While targeting vehicle emissions is crucial, it alone will not be enough to close the air quality gap. Researchers emphasize the need to address systemic factors, such as shifting where emissions occur, and accelerating the adoption of zero-emission vehicles in overburdened communities.

To address these disparities, CARB has intensified its efforts to increase electric vehicle sales in high-need areas, particularly low-income communities. They have also implemented programs such as the Truck and Bus Regulation, targeting heavy-duty diesel vehicle emissions, and the Zero-Emission Vehicle Program, mandating that all new vehicles in California be zero-emission by 2035.

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