How are we doing?
This year, the air quality indicator received a mixed rating. Air quality measures the level of pollution in a specific area, and high pollution levels can harm both residents' health and the environment, especially if they persist for long periods.
Compared to 20 years ago, the region experiences fewer days with poor air quality. In 2024, the Environmental Protection Agency (EPA) adopted stricter federal standards for particulate matter (PM2.5). San Diego’s average annual air pollution slightly exceeded the new standard in 2024, whereas it remained below the limit in 2023 Poor air quality is known to significantly increase the risk of asthma and areas in the southern portion of the county had higher rates of asthma-related, pediatric emergency visits in 2022. Continued efforts to reduce air pollution can improve the air quality of the region and public health for all residents of the region.
Rating: Mixed Results
Air quality has improved over decades, but failed to meet recent stricter federal standards
Air quality index
The U.S. Air Quality Index (AQI) categorizes air quality into six levels, ranging from Good (0-50) to Hazardous (301+), reflecting increasing concerns about pollution. The Equinox Dashboard tracks the number of days each year when San Diego County experiences air quality rated as “Unhealthy for Sensitive Groups”, “Unhealthy”, or “Very Unhealthy”. Sensitive groups include individuals with lung disease, outdoor workers, children, and older adults, though others may also be affected. While the general public is less likely to be impacted by air quality rated as “Unhealthy for Sensitive Groups”, caution is still advised.
In 2024, San Diego County had no days rated as “Very Unhealthy”. However, the number of days rated as “Unhealthy” increased from 0 to 4, while days rated as “Unhealthy for Sensitive Groups” rose from 44 in 2023 to 48 in 2024, indicating that more days posed a risk to the most vulnerable populations.
Increases in days with poorer air quality could be due to a variety of factors. Pollution sources include factories, power plants, vehicles, and wildfires. Heat and droughts can exacerbate polluted conditions because ozone is more efficiently produced in sunny and warm conditions, and wildfires and dust storms are more likely to occur during droughts.
Children's asthma cases in the region
Asthma is a disease that affects the lungs and can be caused by genetic and environmental factors. Poor air quality is known to significantly increase the risk of asthma attacks and subsequent emergency visits. Asthma rates can be a good indicator for understanding a population’s sensitivity to environmental stressors. According to the California Department of Public Health, there were 3,733 cases of asthma-related emergency visits in 2022 among children under 18. The areas of Campo (157.5), College Grove (100.7), Encanto (95.4), Alpine (94.4), and El Cajon (92) had the highest number of emergency visits per 10,000 children. These areas may deal with higher rates of asthma due to exposure to environmental pollution and hazards, such as vehicle exhaust, waste, and hazard sites, as well as challenged socioeconomic conditions, such as poverty and unemployment.
A closer look at particulate matter
PM2.5 (particulate matter) consists of tiny airborne particles or droplets that are thirty times smaller than the diameter of human hair. At high concentrations, PM2.5 can pose health risks, particularly for the respiratory system. Major sources of PM 2.5 include the combustion of fuels such as gasoline, oil, and wood. In San Diego, PM2.5 levels peak between 6:00 and 9:00 p.m., likely due to heavy evening traffic.
Concentrations of PM2.5 can vary daily due to factors such as wildfires, drought conditions, traffic levels, weather, and fireworks. To determine annual averages, monthly PM 2.5 readings were summarized. For 2024, the average annual PM 2.5 level in San Diego County was 9.2 µg/m³ (micrograms per cubic meter). Historically, average PM2.5 levels in the San Diego region have remained below the federal standard. However, in February 2024, the Environmental Protection Agency (EPA) updated its standards for PM2.5, lowering it from 12.0 µg/m³ to 9.0 µg/m³ in response to new research linking air pollution to serious health effects.
Understanding other aspects of air quality
Other common pollutants include carbon monoxide, sulfur dioxide, nitrogen dioxide, and ozone. According to the American Lung Association’s 2025 State of the Air report , the region fares poorly due to high annual PM 2.5 rates and recurring high ozone days, making the region rank as the 8th worst county in the nation for ozone pollution.
University of San Diego undergraduate student, Madeline Sit (‘23), developed a historical analysis of types of air pollution in San Diego County and how it relates to car traffic, wildfire, and rainfall. Click on a card below to explore:
Wildfires
San Diego's arid climate and Santa Ana winds create prime conditions for wildfires. Wildfires are a natural part of the region’s ecosystem, but poorly managed land and precarious infrastructure can lead to disastrous wildfires. Wildfire smoke contains particulate matter, carbon monoxide, and nitrogen oxides, all of which can threaten human health. Wildfires can play a significant role in the quick rise of short-term PM 2.5 levels. The tiny, ultrafine particulate matter can irritate the lungs and eyes and enter the human bloodstream. Wearing masks and running ventilation systems that can filter out these particles can help protect against wildfire smoke.
This map shows large wildfires that occurred in the San Diego region between 2001 and 2021. The 2003 and 2007 wildfire seasons were particularly catastrophic. More recently, the San Diego region experienced large wildfires and related poor air quality in 2020.
Injustice in the air
This research spotlight on Dr. Alberto Pulido and air quality issues in Barrio Logan was developed by Ramona Tellez (‘23)
Poor air quality is experienced unequally across the San Diego region, particularly in urban communities near major freeways. Emissions from cars sitting in traffic worsen air quality and ongoing environmental injustice compounds the problem. To assess this issue, Dr. Alberto Pulido from the University of San Diego and his colleagues at the Environmental Health Coalition quantified particulate organic matter concentrations throughout San Diego County and studied how these values relate with rates of health issues in local communities. The study revealed that air quality is significantly worse in Barrio Logan compared to other parts of San Diego, placing this residential area among the top 5% of most polluted areas in California. Consequently, Barrio Logan residents face an 85% higher risk of developing cancer than the average US population.
Barrio Logan and other neighborhoods in the San Diego Promise Zone face higher levels of pollution due to historic redlining and ongoing forms of displacement. The community of Barrio Logan – primarily made up of immigrants – settled in the area in the early 1900’s, only to face an influx of polluting industries in their neighborhood when the City of San Diego rezoned the area to allow junk yards and metal plating shops. Decades later, the persisting community was split by the construction of Interstate 5 and the Coronado bridge. Though Barrio Logan was later rezoned as “mixed use”, the legacy of environmental injustice still persists.
Related Indicators
- Renewable Energy
- Electric Vehicles
Alternatives to fossil fuels and gas-powered technology help us have a cleaner energy consumption, curbing the emissions of greenhouse gasses and toxic emissions.
Why is air quality important?
High quality of life means the region boasts a thriving economy and a healthy environment accessible to all in the community.
Economy
Air pollution affects the number of days people are able to work and participate in economic activities. Globally, 1.2 billion work days are afflicted by poor air quality and this could triple to 3.8 billion days by 2060. A report by the World Economic Forum found that air pollution costs Americans $2,500 a year in healthcare. Investments in cleaner air quality initiatives can help ensure future economic well-being by safeguarding the health of the working population and the daily conditions for working, shopping, recreation, tourism, and other activities. In California, wildfire events pose a threat to human lives and agricultural crops. The heightened risk of wildfires has resulted in higher insurance premiums for homeowners and some insurance companies stopped offering new home insurance sales in California.
Environment
Air pollution can affect the environment in a variety of ways, including but not limited to acid rain, excess nitrogen in aquatic ecosystems, ozone depletion, crop and forest damage, and climate change. Each of these affect the condition of plants and animals in the region, putting all living things at risk of further species loss and poor environmental conditions.
Equity
People in urban communities are affected disproportionately by various public health issues such as air quality. Low-income and disadvantaged communities in California experience higher air pollution and negative health effects compared to wealthier communities. These communities also often consist of people of color. For instance, freeways built directly through low-income neighborhoods expose residents of color to noise and air pollution, adversely affecting their health. The Barrio Logan neighborhood is an example and ranks among the top five most polluted areas in California.
Regional Response
Policies
On February 7, 2024, the EPA changed the National Ambient Air Quality Standards for particulate matter to reflect new scientific evidence on how particulate matter impacts human health. In 2025 these standards are under review to potentially add flexibility that will accommodate American manufacturing.
The California Air Resources Board’s transportation regulations in effect for 2025 include rules around trucks, buses, and refrigeration transportation.
Rules and regulations by the San Diego County Air Pollution Control District (SDCAPD) can be viewed online.
Projects
The San Diego County Air Pollution Control District hosts a site that displays air quality forecasts of eight different monitoring sites in the county.
The American Lung Association offers yearly report cards on the air quality conditions of metropolitan areas around the nation.
Environmental Health Coalition’s Climate Justice campaign has a strong emphasis on climate policy that includes strategies for clean air.
Partnerships
The County of San Diego and Resilient Shield launched an interactive dashboard that captures the full picture of the Tijuana River Valley sewage crisis which not only affects water quality but air quality as well.
The Environmental Justice Partnership (EJP) is a collaborative effort between San Diego Air Pollution Control District, County of San Diego, California Air Resources Board, community-based organizations, and community members to improve air quality for communities most impacted by pollution. The EJP offered workshops for participating members to develop strategies for reducing air pollution.
U.S.-Mexico border region
In 2020, close to 15 million vehicles crossed the U.S.-Mexico border at San Ysidro, contributing to massive air pollution and high rates of respiratory problems within this border community. A multi-year research project involving the University of Washington, the California Office of Environmental Health Hazard Assessment, and the community organization, Casa Familiar, is tackling this problem by installing air quality monitors and tracking pollution data, which can be used to develop effective pollution mitigation programs. Higher wait times at the border also increases pollutants in the area, because idle cars emit fumes.
What are we tracking?
We report air quality by tracking the number of days when San Diego County’s air is considered unhealthy or very unhealthy for the total population as well as when it is unhealthy for sensitive groups as recorded in the EPA Air Quality Index Report. Air pollution levels measured at a particular monitoring site are not necessarily representative of the air quality for an entire county or urban area. We also measure children’s asthma hospitalization rates by ZIP code throughout the county and report on those areas with 5 or more events. For air pollutants, we specifically focus on annual average PM 2.5 levels in the county. Learn more about the data.