What does 0 bad mean?

The Air Quality Index (AQI) is a measure used by government agencies to communicate air quality levels to the public. It provides a number from 0 to 500, with higher numbers indicating increased levels of air pollution and associated health concerns. A reading of 0 on the AQI represents the best air quality possible, indicating the complete absence of pollutants and associated health risks.

Specifically, a 0 AQI corresponds to zero concentrations of all measured pollutants, including particulate matter, ozone, carbon monoxide, sulfur dioxide, and nitrogen dioxide. This means that at 0 AQI, the air contains none of the hazardous particles or gases that can cause health issues with prolonged exposure. An AQI of 0 signifies air that is perfectly clean and safe for humans and the environment.

In short, 0 on the AQI scale indicates the ideal benchmark for air quality, with no detectable pollution or associated health risks.


The Air Quality Index (AQI) was first introduced in 1968 by the National Air Pollution Control Administration, with the goal of providing a simple way for the public to understand air pollution levels (Wikipedia). The original AQI scale went from 0 to 500, with 0 representing ideal air quality and 500 signifying hazardous pollution levels. This 0-500 scale was devised by the Environmental Protection Agency in 1976 as a consistent system for calculating air quality across the United States (Wikipedia).

The 0-500 AQI scale was designed to be easy to understand, with index values under 100 indicating satisfactory air quality. Readings above 100 suggest air pollution levels that may negatively impact health, especially for sensitive groups. The higher the AQI value, the greater the level of air pollution and associated health concerns.

The Air Quality Index

The Air Quality Index (AQI) is a measurement system used by the Environmental Protection Agency (EPA) and other agencies to communicate daily air quality information. The AQI measures 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 AQI is measured on a scale from 0 to 500. An AQI value of 0 represents the best air quality with little to no risk of health effects, while a value over 300 represents hazardous air quality. In general, the higher the AQI value, the greater the health risk from air pollution exposure. An AQI value under 100 is generally considered satisfactory, though sensitive groups may still experience effects at lower levels.

The AQI measures air pollution concentrations and converts them into a single number and category. Each category corresponds to a likely health impact, with accompanying guidance for the public. For example, an AQI of 50 would be in the “good” range, while 150 would be “unhealthy for sensitive groups.” Understanding the AQI scale helps individuals determine when to modify outdoor activity to reduce exposure.

0 on the AQI Scale

0 represents the best possible air quality and means the concentration of all tracked pollutants is below the minimum federal health standards.[1] According to the AQI scale created by the EPA, an AQI value of 0 means the air is healthy and poses little risk.[2]

When the AQI reads 0, the air contains minimal or no pollutants that are harmful to public health. Specifically, a 0 AQI means:[3]

  • Ozone levels are 0 to 0.054 parts per million (ppm) over 8 hours
  • PM2.5 particle levels are 0 to 12 micrograms per cubic meter (μg/m3) over 24 hours
  • PM10 particle levels are 0 to 54 μg/m3 over 24 hours
  • Carbon monoxide levels are 0 to 4.4 parts per million (ppm) over 8 hours
  • Sulfur dioxide levels are 0 to 0.034 ppm over 24 hours
  • Nitrogen dioxide levels are 0 to 0.053 ppm over 1 hour

Achieving an AQI reading of 0 means the air contains virtually zero levels of common air pollutants. This represents the purest possible air quality.

[1] https://www.airnow.gov/aqi/aqi-basics/
[2] https://www.lung.org/clean-air/outdoors/air-quality-index
[3] https://www.airnow.gov/sites/default/files/2018-04/aqi_brochure_02_14_0.pdf

Ideal Air Quality

Zero (0) on the Air Quality Index represents the cleanest air quality. This is the ideal target because studies show that [even low levels of air pollution can have negative health impacts](https://www.oecd-ilibrary.org/sites/a8ddde8b-en/index.html?itemId=/content/component/a8ddde8b-en). According to the OECD, reducing air pollution has major health benefits including reducing premature deaths, hospital admissions and emergency room visits. It can also reduce the incidence of bronchitis and asthma in children.

Achieving zero air pollution has environmental benefits as well. The IEA reports that reducing air pollution leads to better air quality indoors and outdoors, which improves crop yields, visibility and protects culturally important monuments and buildings from degradation [Multiple Benefits of Energy Efficiency – Analysis (iea.org)](https://www.iea.org/reports/multiple-benefits-of-energy-efficiency/air-quality). Furthermore, zero air pollution eliminates emissions that contribute to climate change, like particulate matter, sulfur oxides, nitrogen oxides and volatile organic compounds.

In summary, 0 readings indicate the cleanest air with significant health and environmental benefits. This makes it the ideal target for air quality.

How Often Does 0 Occur?

According to the AirNow website, readings of 0 on the AQI occur infrequently in most areas. While some remote areas may experience extended periods of 0 readings, most populated areas only reach this ideal air quality level a few times per year. For example, in 2021 the San Francisco area had 0 days with a 0 AQI reading, while Los Angeles had just 2 days. Other major metro areas like New York, Chicago, and Houston also typically see 0 readings just a handful of days annually.

More rural areas and national parks are more likely to experience 0 AQI days on a regular basis due to less air pollution sources. However, even these areas can be impacted sporadically by events like wildfires or dust storms. According to data analyzed by the American Lung Association, many counties across the western half of the U.S. frequently measure 0 AQI days during parts of the year when wildfire smoke is not impacting the region.

In summary, readings of 0 on the AQI tend to be rare events for most populated areas, occurring just a few days out of the year. More remote regions see 0 readings more regularly, but are still subject to periodic pollution influences.

Achieving 0 Readings

There are several ways communities can reach 0 AQI readings through policies and individual actions. According to the EPA, the two most impactful ways are reducing emissions from power plants and vehicles (https://www.lung.org/blog/poor-air-quality-protection).

At the government level, clean energy policies can help transition power generation away from fossil fuels towards renewable sources like wind and solar. Stricter vehicle emission standards can reduce pollution from cars and trucks. Cities can also invest in public transportation infrastructure to get more vehicles off the road.

Individuals can make a difference by walking, biking, carpooling or taking public transit instead of driving alone. Maintaining vehicles well through regular tune-ups and not letting engines idle can also help. At home, choosing clean energy sources, conserving electricity, and avoiding burning wood or trash are small steps everyone can take.

While reaching 0 readings may be difficult for many locations, through sustained community-wide effort, cleaner air and lower AQI levels are an achievable goal.


Achieving a reading of 0 on the AQI scale presents many challenges in today’s world. According to the Air Quality Index (AQI) Basics page on AirNow.gov, “Air quality is satisfactory, and air pollution poses little or no risk” at 0-50 on the index https://www.airnow.gov/aqi/aqi-basics. However, reaching 0 is quite rare with the many manmade and natural contributors to air pollution.

One of the biggest obstacles is emissions from the burning of fossil fuels. Power plants, vehicles, industry, and commercial businesses all emit particulate matter, ground-level ozone, carbon monoxide, sulfur dioxide, and nitrogen dioxide into the air. These pollutants make it very difficult to achieve 0 readings, especially in urban areas.

Fires, both wildfires and planned burns, can also lead to poor air quality and preclude 0 AQI readings. According to an article on Quartz, “Rising global temperatures and increasingly common weather extremes like drought…are creating conditions ripe for massive wildfires” https://qz.com/1913459/what-is-the-air-quality-index. Fires release large amounts of particulate matter, carbon monoxide, volatile organic compounds, and other pollutants.

Even natural sources like windblown dust, pollen, and emissions from vegetation can make reaching 0 AQI difficult depending on weather and seasonal conditions. Overall, the many challenges and complex mix of pollution sources mean that 0 readings tend to be very rare events.

The Future

Experts predict that 0 AQI readings may become more common in the future, especially in major cities that have made efforts to reduce air pollution. With stricter emissions standards, cleaner energy sources, and improved monitoring and regulation, we may start to see more days of ideal air quality.

For example, a report from the Natural Resources Defense Council predicts that by 2030, up to 90 cities in the US could achieve 0 bad air days if they implement plans to cut pollution and transition to electric vehicles and renewable energy (https://www.lung.org/clean-air/outdoors/air-quality-index).

Many other cities globally have set goals to reach 0 unhealthy air days, aided by new technologies like low-cost air quality sensors that provide real-time pollution data. Companies are also developing innovative solutions like smog-filtering buildings to help clean city air.

While progress won’t happen overnight, with continued effort, more cities may start to experience the clean air quality indicated by 0 AQI readings in the coming decades.


Achieving a reading of 0 on the Air Quality Index is important for public health. It indicates that the air contains little to no pollution. There are a number of efforts underway to make readngs of 0 more common, as the public becomes more aware of the dangers of air pollution. While there are challenges, governments and communities are working to improve air quality. Though readings of 0 are still rare in many areas, through continued environmental regulations, transitioning to clean energy sources, and public education, the goal of clean air for all can be achieved.