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Air Quality

Air quality refers to the level of pollutants in the air and their impact on the health and well-being of communities, particularly those living near transit corridors. Poor air quality is often caused by vehicle emissions and industrial activities, and it disproportionately affects vulnerable populations such as low-income communities, communities of color and individuals with pre-existing health conditions. Public transportation plays a critical role in mitigating air pollution by reducing reliance on single-occupancy vehicles and lowering local pollutants (e.g., particulate matter [PM], ozone, carbon monoxide) and greenhouse gas emissions. Different neighborhoods experience disparities in air quality which can have cascading health impacts. Planners should seek to understand a community’s experience and air quality risk factors to align transit infrastructure improvements with public health goals.

Understand your Datasets

Communities near transit corridors or highways often experience higher levels of air pollution, leading to increased rates of respiratory illnesses, cardiovascular disease and other health issues. Particles smaller than 2.5 micrometers (PM2.5) are generally formed by combustion sources like cars, trucks and ships, as well as pollutants mixing or reacting in the air. Ground-level ozone or smog is formed when gaseous pollutants from vehicles react in the presence of sunlight, which can have significant respiratory impacts for local residents. Exposure to air pollutants is of particular concern in urban areas because of the dense populations exposed to air pollution and the high number of emission sources. Short-term respiratory impacts from air pollution range from reduced lung function, coughing and throat irritation to asthma attacks. Longer-term impacts of air pollution include chronic obstructive pulmonary disease (COPD) and cardiovascular disease. PM2.5 can be inhaled very deeply into the lungs, enter the bloodstream and lodge in the heart and brain where they can cause the formation of plaques. Public transit can help mitigate these localized emissions sources and improve health outcomes by reducing the overall number of cars on the road. Monitoring and analyzing air pollution levels, trends in air quality and health impacts can help planners identify areas with poor air quality, assess the impact of transit projects and prioritize investments in active transit and public transit infrastructure. Key metrics to monitor include:

Air Quality Index (AQI)
Pollutant concentrations
Health outcomes
Geographic disparities

Example Datasets:

1. Current Air Quality Data, Air Quality Forecasts and Historical Air Quality Data from South Coast AQMD: https://www.aqmd.gov/home/air-quality

Instructions: The site hosts Current Hourly Air Quality levels housed in an interactive map, along with health recommendations at a neighborhood scale, for the South Coast AQMD jurisdiction. The featured pollutants are PM2.5, O3 (ozone), PM 10, NO2 and CO. Planners may also choose to sign up for Air Alerts for real-time updates.

Data Considerations: The South Coast AMQD is the air pollution control agency for all of Orange County and major portions of Los Angeles, Riverside and San Bernardino Counties. Air Quality Index (AQI) values are determined using a technique developed by South Coast AQMD scientists and published in a peer-reviewed scientific journal that is considerably more accurate than other methods. This method blends measurements from high-quality regulatory monitors, quality-controlled and calibrated low-cost sensors and an air quality model.

2. CalEnviroScreen 4.0: Mapping tool that helps identify California communities that are most affected by many sources of pollution: https://oehha.ca.gov/calenviroscreen/report/calenviroscreen-40

Instructions: The site features an interactive data dashboard along with a user guide, tutorial video and training materials. The site also includes downloadable data files in various formats (e.g., spreadsheets, shapefiles) with results by census tract for users to apply to their own projects, as well as well as an online map of CalEnviroScreen 4.0 results.

Data Considerations: This mapping tool identifies areas most affected by multiple forms of pollution, where communities are often especially vulnerable to pollution’s effects. The tool was developed and refined through over 10 years of collaboration between community-based organizations, scientists, academia, industry, government agencies, tribal representatives and members of the public.

Community Demographics Profiles Alignment

CES 4.0 Score
Healthy Places Index

Explore the Index of Indicators in Metro’s Community Demographics Profiles Dashboard here.

Coordinate with Community Members

Supplement information derived from your datasets with historical records of air quality and community member experiences. Consider implementing a community-led air quality monitoring system that empowers residents to collect and track their own data, as well as provides an accountability mechanism for local governments. Public health outcomes from poor air quality can be difficult to quantify and document, but by identifying areas with high rates of respiratory illnesses, asthma and other conditions linked to air pollution exposure, as well as identifying areas with high pollution levels and prioritizing interventions in these locations, planners can mitigate negative health and environmental impacts. Air quality impacts drivers, public transit users and those walking, biking and rolling, all of whom are exposed to air pollutants, pollution from brake dust/tire wear and traffic, which can all have negative health outcomes. Consider how your project may impact air quality in the short and long term and how to better align with community member priorities. If applicable, consider implementing a construction management plan and dust suppression measures to reduce PM 10.

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