The Air Quality Index (AQI) translates complex air pollution data into easily understandable terms for the public. This index converts the concentrations of multiple air pollutants, such as ground-level ozone and particulate matter, into a single numerical value. The primary function of the AQI is to inform individuals about the current air quality in their area and communicate the potential associated health risks. The system uses a simplified, color-coded scale to help people make informed decisions about their outdoor activities.
The Significance of the Green Category
The color associated with “Good” air quality on the index is Green. This Green category corresponds to an AQI numerical range of 0 to 50. Air quality in this range is considered satisfactory, meaning that air pollution poses little to no health concern for the population.
This is the condition for optimal outdoor activity, as the air is safe for all groups, including the young, the elderly, and those with pre-existing heart or lung conditions. When the AQI is Green, the air contains minimal concentrations of pollutants like fine particulate matter (PM2.5) and ozone. This allows the entire population to enjoy unrestricted outdoor exercise and ventilation of homes without the need for health precautions.
Decoding the Full Air Quality Index Scale
The index is divided into six standardized levels, each assigned a specific color and numerical range indicating increasing health concern. Following Green is the “Moderate” category, which is represented by the color Yellow and spans an AQI from 51 to 100. Air quality is acceptable here, though a very small number of individuals who are unusually sensitive to pollution may experience minor health effects.
The third level is “Unhealthy for Sensitive Groups,” marked by the color Orange and a range of 101 to 150. This is the first level where the air is considered potentially harmful, specifically for children, older adults, and people with respiratory diseases like asthma. Progressing to the color Red indicates “Unhealthy” air quality, covering the range of 151 to 200, where the general public may begin to experience adverse health effects from prolonged exposure.
The final two categories signal very high levels of pollution that pose serious risks to everyone. The color Purple designates “Very Unhealthy” air, with an AQI from 201 to 300, leading to a health alert where the risk of health effects is significantly increased for everyone. The highest, most severe category is “Hazardous,” which is represented by the color Maroon or Dark Red and includes all AQI values from 301 to 500. Air quality in this range triggers emergency health warnings because the entire population is likely to be affected.
Practical Health Guidance for Each AQI Level
During the Yellow, or Moderate, level (51–100), the general public can continue with normal outdoor activities. However, sensitive individuals should consider reducing the intensity or duration of their outdoor exertion. This advice is especially relevant for people with conditions like COPD or asthma, who may experience mild symptoms from prolonged exposure.
When the air quality shifts to Orange (101–150), the recommendations become more focused on reducing exposure for vulnerable populations. Sensitive groups, including children and older adults, should actively limit their time outdoors and take more breaks during any necessary outdoor activities. Healthy individuals may still be able to engage in outdoor exercise, but they should be aware of potential minor symptoms with extended exposure.
At the Red level (151–200), the health alert extends to everyone, and the recommendations become more stringent for all people. Sensitive groups are strongly advised to stay indoors and avoid all outdoor exertion to prevent more serious health effects. The general population should also limit prolonged or heavy exertion outdoors, as chest tightness or random coughing can become more common.
The most severe categories, Purple (201–300) and Maroon (301–500), require significant changes in daily behavior. In the Purple range, health effects have increased for everyone, and outdoor activities should be severely restricted. Once the AQI hits Maroon, the entire population faces a health emergency, and everyone should avoid all outdoor exertion and remain indoors to protect against immediate and serious complications.