Photos depicting the Open Air Chicago process from assembly to installation
Open Air Chicago is built on openness and transparency. By sharing clear, accessible air quality data, the project helps Chicagoans understand the air they breathe and make informed choices to protect their health and communities.
Anyone can explore Open Air Chicago through the Clarity Open Map and the Chicago Open Data Portal.
Use the Clarity Open Map to:
- Identify the air sensor(s) near you
- Assess current air quality levels and 24-hour trends
- Review health recommendations related to the current air quality
- Download measurements from the last 30 days for a specific sensor
- Sign up to receive alerts from a specific sensor when air quality becomes “unhealthy”
Use the Chicago Open Data Portal to download raw and weighted data for:
- Individual measurements
- Hour aggregations
- Day aggregations
Visit the Chicago Open Data Portal
| AQI Categories (Index Values) | PM2.5 (24-hour) | NO2 (1-hour) |
|---|---|---|
| Good (0-50) | It's a great day to be active outside! | It's a great day to be active outside! |
| Moderate (51-100) | Unusually sensitive people: Consider making outdoor activities shorter and less intense. Go inside if you have symptoms such as coughing or shortness of breath. | Unusually sensitive people: Consider limiting prolonged exertion especially near busy roads. |
| Unhealthy for Sensitive Groups (101-150) | Sensitive groups: Make outdoor activities shorter and less intense. It's OK to be active outdoors but take more breaks. Watch for symptoms such as coughing or shortness of breath. | |
| People with asthma: Follow your asthma action plan and keep quick relief medicine handy. |
People with heart disease: Symptoms such as palpitations, shortness of breath, or unusual fatigue may indicate a serious problem. If you have any of these, contact your health care provider.
| Sensitive groups: Limit prolonged exertion outdoors, especially near busy roads.
People with asthma: Follow your asthma action plan and keep quick relief medicine handy.
| | Unhealthy (151-200) | Sensitive groups: Consider rescheduling or moving all activities inside. Go inside if you have symptoms.
People with asthma: Follow your asthma action plan and keep quick-relief medicine handy.
People with heart disease: Symptoms such as palpitations, shortness of breath, or unusual fatigue may indicate a serious problem. If you have any of these, contact your health care provider.
Everyone else: Keep outdoor activities shorter and less intense. Go inside if you have symptoms.
| Sensitive groups: Avoid prolonged outdoor exertion near roadways.
People with asthma: Follow your asthma action plan and keep quick relief medicine handy.
Everyone else: Limit prolonged outdoor exertion especially near busy roads
| | Very Unhealthy (201-300) | Sensitive groups: Avoid all physical activity outdoors. Reschedule to a time when air quality is better or move activities indoors.*
People with asthma: Follow your asthma action plan and keep quick-relief medicine handy.
People with heart disease: Symptoms such as palpitations, shortness of breath, or unusual fatigue may indicate a serious problem. If you have any of these, contact your health care provider.
Everyone else: Limit outdoor physical activity. Go indoors* if you have symptoms.
| Sensitive groups: Avoid all outdoor exertion.
Everyone else: Avoid prolonged outdoor exertion especially near busy roads. People with asthma: Follow your asthma action plan and keep quick relief medicine handy
| | Hazardous (≥ 301) | Sensitive groups: Stay indoors and keep activity levels light. Follow tips for keeping particle levels low indoors.*
People with asthma: Follow your asthma action plan and keep quick-relief medicine handy.
People with heart disease: Symptoms such as palpitations, shortness of breath, or unusual fatigue may indicate a serious problem. If you have any of these, contact your health care provider.
Everyone: Avoid all physical activity outdoors.*
| Sensitive groups: Remain indoors.*
People with asthma: Follow your asthma action plan and keep quick relief medicine handy.
Everyone else: Avoid all outdoor exertion.
|
*Note: If you don't have an air conditioner, staying indoors with the windows closed may be dangerous in extremely hot weather. If you are hot, go someplace with air conditioning or call 311 to find cooling centers near you in Chicago.
Frequently Asked Questions 
Data can be delayed for several reasons, including inadequate cellular service, battery levels, sensor clogs, and loosening power cords. 
If you notice high readings of the Air Quality Index (AQI), please refer to the AQI guide above. 
Monitoring data can show short-term spikes of PM2.5 and NO2. Health-based PM2.5 and NO2 air quality exposure standards consider exposure rates averaged over one hour to one year. Regulators have not established health-based standards for exposure periods of less than one hour, which is one of the reasons why AQI is only reported as hourly averages. Air quality can change slowly or rapidly depending upon the weather, wind direction, time of day, inversion layer conditions, and other factors. Given the variability in air quality conditions, it is important to be aware but also prudent in how to respond in different situations. 
- Facility or fenceline monitors are required at certain permitted industrial facilities, with information submitted to CDPH.
- Regulatory monitors are operated by IL EPA and the Cook County Department of Environment and Sustainability with oversight by the U.S. Environmental Protection Agency Air and Radiation Program. There are approximately six federal air monitoring sites in Chicago. Federal Reference Monitors (FRMs) and Federal Equivalent Monitors (FEMs) are regulatory-grade air monitoring instruments specifically designed to assess compliance with the health-based National Ambient Air Quality Standards (NAAQS) by the U.S. EPA.
- Low-cost sensors such as PurpleAir or AirBeam are operated by residents, organizations, and researchers to help identify hot spots and understand relative air quality levels and trends across Chicago neighborhoods using non-consistent monitoring protocols employed by users.
- Clarity Node-S sensors used by Open Air Chicago deliver high-quality data when properly tested and maintained. However, these sensors are not regulatory-grade instruments and cannot be used in support of regulatory decision-making (e.g., permitting, compliance assessment with NAAQS, or enforcement).
Major air pollution sources in Chicago include mobile sources (i.e., transportation sources such as cars, trucks, planes, and trains) and stationary sources (i.e., industrial facilities that burn fossil fuels like factories).   
Nitrogen dioxide (NO2) primarily gets in the air from the burning of fuel, from transportation sources (cars, trucks) and also industrial sources (e.g., factories, etc). NO2 is also formed in air when nitric oxide (NO) from these air pollution sources reacts with other pollutants in ambient air such as ozone. NO2 along with other NOx reacts with other chemicals in the air to form both particulate matter and ozone. 
Particulate matter is emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires. Most particles form in the atmosphere because of complex reactions of chemicals, such as sulfur dioxide and nitrogen oxides, which are pollutants emitted from industries and automobiles. 
Breathing air with a high concentration of NO2 can irritate airways in the human respiratory system. Such exposures over short periods can aggravate respiratory diseases, particularly asthma, leading to respiratory symptoms (such as coughing, wheezing or difficulty breathing), hospital admissions and visits to emergency rooms. Longer exposures to elevated concentrations of NO2 may contribute to the development of asthma and potentially increase susceptibility to respiratory infections. People with asthma, as well as children and the elderly, are generally at greater risk for the health effects of NO2.  
The size of particles is directly linked to their potential for causing health problems. Small particles less than 10 micrometers in diameter pose the greatest problems, because they can get deep into your lungs, and some may even get into your bloodstream. Exposure to such particles can affect both your lungs and your heart. Numerous scientific studies have linked particle pollution exposure to a variety of problems, including premature death in people with heart or lung diseases, nonfatal heart attacks, irregular heartbeat, aggravated asthma, decreased lung function, and increased respiratory symptoms, such as irritation of the airways, coughing or difficulty breathing
Sensitive populations who are more vulnerable than others to air pollution include: 
- Children 
- Older adults 
- Individuals who are pregnant and their fetuses 
- People living with asthma, COPD and other chronic diseases 
- People of color 
- People who have lower income 
- People who live or work near sources of pollution 
- People who work outdoors