Days with an EPA Air Quality Index Rating of "Good"
The U.S. Environmental Protection Agency (EPA) calculates and publishes an Air Quality Index (AQI) each day based on real-time monitoring by the Bay Area Air Quality Management District at a single location in San Francisco. This location monitors five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide.
|Air Quality Index||Numerical Value||Meaning|
|Good||0 to 50||Air quality is considered satisfactory, and air pollution poses little or no risk.|
|Moderate||51 to 100||Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.|
|Unhealthy for Sensitive Groups||101 to 150||Members of sensitive groups may experience health effects. The general public is not likely to be affected.|
|Unhealthy||151 to 200||Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.|
|Very Unhealthy||201 to 300||Health alert: everyone may experience more serious health effects.|
|Hazardous||301 to 500||Health warnings of emergency conditions. The entire population is more likely to be affected.|
Due to its geography, local meteorology, and limited industrial activity, the County of San Francisco has relatively good air quality. However, in many parts of the county, concentrations of air pollutants may exceed health-protective standards. Thus, improving citywide air quality is a priority because of its strong relationship to numerous adverse health outcomes. Most well-known are the adverse respiratory effects such as aggravated asthma, chronic bronchitis, and reduced lung function. Air pollution also affects heart health and can trigger heart attacks and strokes, and air pollutants may be a contributing factor to leading causes of death recorded for San Francisco’s population. Causes include ischemic heart disease, lung, bronchus, and tracheal cancers and lower respiratory infection. Exposure to air pollutants that are carcinogens can also have significant human health consequences like lung cancer.
EPA Air Quality Rating by Year
How San Francisco is Performing
Mobile sources of air pollution from cars, trucks, ships, emissions from construction equipment, and tire and brake wear on roadways are the biggest root cause of poor air quality in the city, and addressing these should result in positive air quality trends. Between 2000 and 2007, the number of “Good” air quality days remained relatively steady, between 244 and 291, and then fell to a low of 196 in 2009. The annual number of days with “Good” air quality has increased since then to a high of 310 in 2016; however, there is no clear indication that the trend toward improvement is permanent. The number of days with "Good" air quality was 276 in 2017 and increased to 278 in 2018. Annual data is available at the end of the following year.
San Francisco has increasingly fewer stationary sources of air pollution, as power plants in Hunters Point and Potrero Hill were closed in 2006 and 2010, respectively, and many industrial businesses have since left the city. This has led to a decrease in the number of days with “Poor” air quality, yet the number of days with “Good” air quality has not significantly improved. While air pollution from the mobile sources mentioned above are the biggest root cause of poor air quality, pollution from stationary sources such as diesel generators, gas stations and dry cleaners continue to contribute to poor air quality in the city.
A 2008 ordinance, San Francisco Health Code Article 38, was adopted to require new residential construction projects, located in areas where computer models show poor air quality and pollution from roadways, to install enhanced ventilation to protect residents from the health effects of living in a poor air quality area. The law was updated in 2014 to improve consistency with California Environmental Quality Act (CEQA) and streamline implementation. Additionally, the San Francisco Department of Public Health is working to foster interagency collaboration and coordination for policy development using evidence, as outlined in the Community Risk Reduction Plan (CRRP). The CRRP will provide a comprehensive, community-wide approach for reducing local air pollution emissions and exposures.
This data is being tracked as part of DPH’s Strategic Plan and staff in the Environmental Health Branch is coordinating with multiple city agencies and the Bay Area Air Quality Management District to support policies and programs that reduce emissions and human exposure to air pollution.
How Performance is Measured
The EPA calculates and publishes the AQI each day based on real-time monitoring by the Bay Area Air Quality Management District at a single location on Arkansas Street in San Francisco. This location monitors five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide.
The number displayed on the scorecard page represents the 2018 value in the chart above.
Learn more about Article 38 of the San Francisco Health Code.
For the latest air quality updates for your area, visit airnow.gov.
For the count of Air Quality Days by category, visit www.epa.gov/outdoor-air-quality-data/air-quality-index-report.
Please click first on the chart above and then click the “Download” button in the bottom right corner of the visualization to view and download the data displayed in the chart.