400 AQI: Good or Bad?

The below article talks about the air quality index (AQI), how to understand them, how it impacts your daily life, along with some frequently asked questions about air quality and using the air quality index. 

Is 400 AQI Good?

No, an AQI of 400 is very bad and must be avoided at all costs. It is considered an emergency circumstance and is a potential hazard to citizens in the area. It can have devastating impacts on health and these can be short-term or long-term depending on the person’s age, sex, history of health, previously diagnosed illnesses, etc. along with many other factors. If there is a projection or forecast of 400 AQI, it is best to stay indoors or stay in an area with better air quality, wear masks and take other protective measures,

Air pollution and air quality

Poor air quality due to increasing pollution is an extensively studied field. The effects of exposure to bad air quality are inevitable and researchers have taken up various measures to identify the different impacts air-borne pollutants could have. Air pollution has been found to impact human health severely and if exposed to it on a long-term basis, it could cause irreversible damage including respiratory conditions and neuro system damages amongst other illnesses. 

Research into air pollution in the top 30 cities in the world shows that Indian cities hold the first 21 positions and that in 2019, approximately 1.67 million deaths were attributed to long-term exposure to poor air quality. The long-term exposure to high levels of air pollution caused heart attacks, chronic lung diseases, strokes, along with neonatal diseases which were accelerated due to the poor air quality (Hadley S., 2020). 

Various countries have taken measures to ensure clean air. For example, cities like Birmingham and Madrid aim to create “clean air zones” by enforcing strict regulations within the inner-city borders, China has acknowledged the need to speed up the construction and usage of electric vehicles to ensure that decent levels of air quality can be maintained in the country, Bangladesh high court has put together several directives aimed at ministries across the country to take actions to counter the effects of air pollution on its citizens (Hadley S., 2020).

Sources of exposure to poor air quality

Air pollution and its effects can be seen globally across rural and urban areas. Exposure to poor air quality can occur indoors or outdoors and some of the sources are the following:

  • Smoke and fumes from vehicles, factories, fires, power plants, burning waste, heating systems, firecrackers, etc. 
  • Smog from indoor or outdoor fire sources
  • Tobacco smoke from primary usage or second-hand exposure
  • Burning fuel sources at close quarters like coal, oil, and wood
  • Occupational exposure such as paint fumes, varnish, automobile fumes, etc. 
  • Chemicals from cleaning agents, pesticides, paints, etc. 
  • Exposure from long-term pollutant sources like asbestos or lead paint
  • Allergens, mold spores, dander, pollen, etc. 

Prolonged exposure to poor air quality could translate to the following physical symptoms – coughing, wheezing, irritation and inflammation of eyes/ throat/skin, respiratory difficulties, chronic fatigue, breathlessness, diminished lung capacity, etc. If any of these symptoms are observed in pregnant individuals, it is best to consult a medical professional for help and counsel. 

Air Quality Index (AQI)

An AQI is used by global and national state actors to communicate to the public about the levels of air quality in the country and the world. As AQI levels increase, health risks increase and different countries have different interpretations of the same index, therefore the levels of measures taken across countries will differ. Countries can have their own indices, scales, and national air quality standards. Therefore, governmental monitoring stations may show different data in comparison to other global sources. 

Analysis of AQI is done through a collection of a large amount of data collected over large periods of time with the help of various devices, sensors, and monitors that measure the levels of different pollutants and toxic airborne particular matter. These values are studied to identify air pollution patterns and create projections that help citizens worldwide to make decisions about their everyday activities. Various studies have been conducted globally to study the correlation between different levels of air pollution and the health impacts it creates, and they have proven time and time again that the AQI is an important measure and needs to be strictly adhered to in order to reduce the long-term health effects on individuals. 

The objectives and goals of having an AQI are as follows:

  • It aims to compare air quality conditions across different locations around the world.
  • It helps to identify inefficient standards and frameworks; and aims to put pressure on global actors to take necessary actions to fix these gaps.
  • It helps to identify patterns of change and distribution of air quality and toxic air pollutants 
  • It informs global citizens on air quality conditions and what protective measures need to be taken to safeguard themselves and their families. 

There is a large number of air pollutants, and varying concentrations of these pollutants cause different effects across various populations. The US EPA (Environmental Protection Agency) identifies 5 major pollutants (US EPA, n.d.). They are as follows:

  • Ground-level ozone 
  • Particulate matter such as PM2.5 and PM10  
  • Carbon monoxide (CO)
  • Sulfur dioxide (SO2)
  • Nitrogen dioxide (NO2)

Each of these pollutants has a globally set standard so that countries may know at what levels these pollutants will get toxic, and thus be able to take public health measures. 

The air quality scale

Below is a table of the air quality standards followed in the US. This is mostly followed by countries everywhere and any interpretations made only vary very little in comparison to this table. 

Source: AirNow, n.d. 

In general, air quality is measured on a numbered scale from 0 to 500, and they are divided into different color-coded categories based on the severity of the levels of air quality. Below are the commonly followed categories (BS, n.d.):

  • 0 – 50 (Good / Minimal Impact) – The air quality is considered to be within healthy limits and poses little to no risk to the citizens in the area. 
  • 51 – 100 (Satisfactory / Moderate Impact) – Air quality is acceptable, but can pose a risk. The air quality can cause minor difficulties in breathing to vulnerable populations amongst the citizens in the area.
  • 101 – 200 (Moderately Polluted/ Unhealthy) – Air quality is not under acceptable levels and can cause difficulties in citizens in the area, especially amongst individuals with respiratory illnesses or other diseases. 
  • 201 – 300 (Poor/ Very Unhealthy) – Air quality levels are high and can cause distress in citizens with prolonged exposure to these levels. It is a health risk to vulnerable populations and they need to be on alert. 
  • 301 – 400 (Very Poor/ Hazardous) – Poor air quality levels and pronounced effects on vulnerable populations, and respiratory illnesses to other citizens on prolonged exposure. 
  • 401 – 500 (Severe) – Toxic levels of air pollution and need to be considered as a health warning for all with a special focus on vulnerable populations. Everyone will be affected and can have long-term impacts even with short-term exposure. 

Protecting yourself from poor air quality 

Outdoor air quality is an important factor that plays into the well-being of one’s physical health. While there is no way to completely protect yourself from poor air quality, here are some preventative measures you can take to avoid or reduce the impacts it could have on your physical health:

  • Periodically check air quality forecasts to ensure that you stay indoors during peak hours of poor air quality. 
  • Limit your exposure to poor air quality especially during traveling or being in traffic.
  • Wear masks to reduce the intake of airborne pollutants into your bloodstream through the respiratory system
  • Wear protective glasses or sunglasses to protect your eyes from long-term exposure to air pollution as pollutants can enter your body through your eyes as well
  • Using alternatively fueled items such as hand-powered or electrically powered devices. 
  • If you have been diagnosed with asthma, make sure to carry your inhaler at all times and make a note to stay away from heavily polluted areas
  • Stay away from tobacco smoke and ban indoor smoking.
  • Ensure proper indoor air quality through proper ventilation and exhaust fans, or by installing an air purifier. 
  • Get rid of unwanted chemicals such as strong cleaning agents, paints, air fresheners, hairsprays, varnishes, etc. 
  • Use natural products wherever and whenever possible, especially for cleaning and maintenance purposes
  • Ensure that all ventilation systems are periodically monitored and cleaned, this also includes changing or cleaning the filters in your air purifier
  • Have periodical assessments of indoor air quality with help from consulting professionals from an environmental monitoring company 
  • Get air purifying plants as they are a natural and eco-friendly solution to cleaning the air and producing fresh oxygen
  • Invest in air quality monitors, sensors, or alarms that can measure indoor air quality at all times and alert you when the air quality is poor or when a certain pollutant’s concentration has increased. 

Frequently Asked Questions (FAQs): Is 400 AQI good or bad?

Does wearing a mask protect you from the effects of poor air quality? 

Yes, wearing masks is immensely beneficial to protect yourself from the adverse impacts of poor air quality on your health. Different kinds of masks provide different levels of protection, depending on the type of filtration it is capable of. With the COVID-19 Pandemic, wearing a mask has been made compulsory worldwide, and has proven to be effective in keeping away various contaminants. This practice will need to be continued to protect global citizens from the devastating impacts of bad air quality on respiratory systems. 

Does wearing a contact lens protect my eyes from toxic air pollutants? 

No, wearing contact lenses increases the risk of eye irritation as they already cause dry eyes. This leads to increased discomfort, irritation, or conjunctivitis from pollutants from the air. 

What countries or cities have the highest levels of air pollution in 2021?

As of 30 November 2021, the most polluted cities are (IQAir, 2021):

  1. Lahore, Pakistan – 350 AQI
  2. Delhi, India – 232 AQI
  3. Kolkata, India – 192 AQI
  4. Kabul, Afghanistan – 177 AQI
  5. Tehran, Iran – 167 AQI
  6. Shanghai, China – 165 AQI
  7.  Zagreb, Croatia – 164 AQI
  8. Dhaka, Bangladesh – 162 AQI
  9. Hanoi, Vietnam – 162 AQI
  10. Ulaanbaatar, Mongolia – 156 AQI 

Other FAQs about Air Quality that you may be interested in.

Can bad air quality cause a fever?

Can poor air quality affect your eyesight?

Can poor air quality cause Hives?


Business Standard (BS). (n.d.). What is Air Quality Index (AQI)? Viewed on 11-29-2021. https://www.business-standard.com/about/what-is-air-quality-index 

Environmental Protection Agency (US EPA). (n.d.). Criteria Air Pollutants. Environments and Contaminants. Viewed on 11-29-2021. https://www.epa.gov/sites/default/files/2015-10/documents/ace3_criteria_air_pollutants.pdf 

IQAir. (2021, November 30). Air quality and pollution city ranking. Viewed on 11-30-2021. https://www.iqair.com/world-air-quality-ranking   

Hadley S. (2020, December 21). Air Pollution is causing Permanent Damage to eye health. Viewed on 11-29-2021. Earth.org. https://earth.org/air-pollution-causing-damage-to-eye-health/ 

AirNow. (n.d.). Air Quality Index (AQI) Basics. Viewed on 11-29-2021.  https://www.airnow.gov/aqi/aqi-basics/ 

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