What are the indicators of air quality?

The environmental protection agency (EPA) has set some National Ambient Air Quality standards for six major air pollutants known as Criteria Pollutants.  Based on the concentration level of each pollutant a certain value is assigned between the range 0-500.This determines the Air Quality Index of a particular place. 

So, in this article we will discuss the criteria pollutants, what are the indicators of air quality,how do we depict the Air Quality Index, what are the health impacts and what measures we can take to protect ourselves from the impact of harmful pollutants. So read this article till the end to know more. 

What are the indicators of air quality?

According to the environmental protection agency (EPA) the 

Criteria pollutants are the basic indicators of air quality. 

The higher the concentration of these pollutants in the ambient air the higher the pollution levels. 

So the indicators of Air Quality are as follows:

The six criteria pollutants are 

  • Sulfur dioxide
  • Nitrogen dioxide
  • Ozone
  • Carbon monoxide
  • Particulate matter 10 and PM2.5
  • Lead

How is the air quality index depicted? 

The concentration of the criteria pollutants in the ambient air tells us about the air quality.

The following table depicts the Air Quality Index

Air Quality IndexLevels Color coding 
0-50  Good Green 
51-100 Moderateyellow
101-150 Unhealthy For  Sensitive Groups Orange 
151-200  UnhealthyRed
201-300  Very Unhealthy Purple
301-500  Hazardous Maroon

What are the sources and health impacts related to these pollutants?

Sulfur Dioxide

Sulfur Dioxide is an irritant gas. If you happen to inhale this gas it can irritate your nose, throat and lungs. 

Sources of Sulfur Dioxide 

 The most common sources includes; 

  • Coal fired power stations
  • Oil refineries
  • Shipping
  • Coal burning
  • Diesel vehicles

Health impacts of Sulfur Dioxide

If you are exposed to a high concentrations of SO2 then it can cause symptoms like;

  • Wheezing
  • Coughing
  • Shortness of breath
  • People having existing lung conditions are more prone to its effects. 

Nitrogen Dioxide

Nitrogen dioxide is a gas. When inhaled it can cause irritation in your throat and lungs. 


Sources of Nitrogen Dioxide

The main sources of NO2 are: 

  • Vehicular traffic
  • Coal powered stations
  • Industrial emissions 

Health effects 

  • Health effects caused by NO2 includes:
  • Coughing
  • Wheezing
  • Shortness of breath
  • It can worsen the condition of people with lung conditions.


Ozone is a pungent gas which is present in the stratosphere. It protects us from the effects of harmful UV rays. But when formed at ground level it causes several harmful effects. Ozone is the main component of photochemical smog. 

Sources of Ozone

When the oxides of nitrogen and certain volatile organic compounds react with each other in the presence of sunlight, it gives rise to ground level ozone. 

Health impacts of Ozone

  • Exposure to this toxic gas can irritate your throat and lung linings. 
  • Causes difficulty in breathing
  • The people at higher risk includes; children, elderly, and people with lung conditions.

Carbon monoxide

CO is a colourless odourless and toxic gas. 


Major sources of indoor carbon monoxide:

  • leaking chimneys and furnaces, 
  • wood stoves, gas stoves, 
  • generators 
  • gasoline-powered equipment
  • tobacco smoke

 Health effects

Health effects can vary depending upon the concentration. For example

  • At low concentrations, it can cause fatigue in healthy people and chest pain in people with heart    disease
  • At moderate concentrations it can cause angina, impaired vision and reduced brain function.  
  • However at higher concentrations it can cause impaired vision and coordination, dizziness, confusion, nausea and fatal at high concentrations

PM10 particles

The PM10 particles are defined as particles having the size range of either 10 or less than 10 microns. These particles are small enough to enter your throat as well as lungs. 

Sources of PM10

Common sources include:

  • Dust
  • Fire smoke
  • Vehicular exhausts
  • Industrial emissions


Health effects

If exposed to high levels PM 10 can cause symptoms of:

  • Coughing
  • Runny nose
  • Stinging eyes

It can cause the symptoms of chest tightness and breathing difficulty in people having lung and heart disease. 


PM2.5 particles

PM2.5 are the particles having the size of 2.5 microns or smaller. PM2.5 is very small in size. It is mainly found in smoke.

Sources of PM2.5

  • Common sources includes:
  • Smoke from fires
  • Vehicular exhaust 
  • Industrial emissions 


Health impacts of PM2.5

PM2.5 if inhaled in high quantities can cause:

  • Wheezing
  • Coughing
  • Chest tightness
  • Difficulty in breathing 

These particles are so tiny that they can penetrate deeper into your lungs and can even enter your bloodstream and travel to other parts of the body.


Lead is a naturally occurring element which is found in earth’s crust in small amounts. 

Its exposure is harmful to both humans and animals. 

Sources of lead

  • The most common sources of lead are anthropogenic which includes:
  • Leaded gasoline
  • Lead based paints
  • Ceramics
  • Pipes
  • Batteries 
  • Cosmetics
  • Ammunition
  • Spark-ignition engine aircraft 

Health effects of lead 

  • It can cause cardiovascular diseases; like hypertension
  • Can decrease the kidney function
  • Cause reproductive problems 
  • Behavioural and hearing problems in children 
  • Anemia in children 
  • Increase the risk of miscarriage 


How can you limit your exposure to harmful pollutants?

Monitor air pollution levels

You can keep a check on the air quality index of your area to get insight about the pollution levels. There are certain websites designed for this purpose such as the Environmental Protection Agency. These sites can be accessed anytime of the day.

Plan any outdoor activities in morning 

During early mornings, the pollutant concentrations; particularly the ground level ozone, are lower as compared to mid afternoon. So you can plan your activities in the mornings. However, If the AQI has reached harmful levels you can schedule your outdoor activities to the next day. 

However the normal physical activities can be performed indoors under controlled conditions like air conditioners and air purifiers when ozone concentrations are high outside. 

Below is the activity recommendation table that will help you to choose the right time for outdoor activities:

Air Quality IndexShort duration (15 mins )Duration for Prolonged exertion (1 hour)Duration for strenuous activities( 2-4+ hrs)Duration for scheduled activities like sports events 
0-50  Good Safe for outdoor activities Safe for outdoor activities Safe for outdoor activities Safe for outdoor activities 
51-100 ModerateSafe for outdoor activities Safe for outdoor activities Safe for outdoor activities Safe for outdoor activities 
101-150  Unhealthy For      Sensitive Groups Short duration physical activities can be done Ideal for mild physical activities Ideal for mild physical activities with frequent rest periodsIdeal for mild physical activities with frequent rest periods
151-200  UnhealthyShort duration physical activities can be done but watch for symptoms like coughing and shortness of breath Mild exercise can be done but watch for symptoms like coughing and shortness of breath Avoid doing strenuous exercises with frequent rest periods All the outdoor  activities should be reschedule or relocation is ideal in this situation 
201-300  Very Unhealthy Restrict outdoor activity, preferably stay indoorsRestrict outdoor activity, preferably stay indoorsRestrict outdoor activity, preferably stay indoorsAll the outdoor activities should be reschedule or relocation is ideal in this situation

Check for particle pollution concentration: 

Particle Pollution (PM2.5): when the concentration of PM2.5 is high in the ambient air, the air quality both outdoors and indoors gets affected. In this case the amount of outdoor physical activities should be limited. 

In such a case, installing air purifiers and HVAC systems will improve the indoor air quality. 

By installing air purifiers

Given below are the links of few air purifiers that will keep your house clean and safe:

Air purifier : GermGuardian Air Purifier

  • Features: Germ guardian 5 in 1 air purifier is an electrostatic HEPA air filter and offers a removal efficiency of about 99.97% against particles as small as 0.3 microns. 
  • Efficiently removes harmful germs like viruses, odor causing bacteria, mold spores, mildew, and other allergens like;  dust, pet hair, and other large particles; like PM10
  • The efficient UV-C light kills airborne viruses such as influenza, staph and rhinovirus. 
  • The filter also removes the VOC concentration with the help of titanium dioxide. 
  • The activated charcoal filter is effective against cooking odor, tobacco smoke, fumes, pet odor etc. 
  • Offers quiet operation; with the Ultra-quiet sleep mode it operates on low sound levels to get you a good night’s sleep.  
  • GermGuardian Air Purifiers are ideal for medium to large rooms having an area of about 743 sq ft.

Air purifier: Instant Air Purifier

  • Features: Instant air purifiers are proven to kill 99.9% of Covid-19 virus, bacteria, mold, and other harmful viruses. 
  • With its Advanced 3-in-1filtration; HEPA-13, Activated Carbon, Antimicrobial coating and plasma ion technology it removes 99.97% of pollutants like particulate matter tobacco smoke, pet dander, certain odors and other impurities. 
  • Its advanced sensors offer a 24×7 air quality monitoring with auto fan speed adjust feature.
  • It filters the air in an area of 126 sq ft 5x per hour 
  • With its whisper quiet night mode it offers lower noise for a sound sleep.
  • The filters last upto 8 month, after that it needs to be replaced.


By installing an HVAC systems 

The HVAC system works efficiently towards filtering airborne contaminants and also helps in continuous circulation of air.

Given below are the links of few HVAC systems that will keep your house clean and safe:

HVAC System:  Honeywell F300E1019 Electronic Air Cleaner

  • Features: This can be operated with gas, oil and AC systems. 
  • Efficiency for capturing particles is upto 98%.
  • Has a very low pressure drop

HVAC System: DAIKIN Inverter Air Conditioner Heat Pump System

  • Features: Daikin’s ductless technology offers  greater  energy efficiency; cools and warms up the room fast.
  • Smart inverter technology with integrated inverted variable speed compressor
  • Provides continuous heating and cooling with minimum temperature fluctuations.
  • Quiet operation; with indoor sound levels as low as 37 decibels. 

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

What are PM2.5 particles?

How is the air quality in Long Beach?

Fossil Fuels and Air Pollution


So, in this article we discussed what are the indicators of air quality, how do we depict the Air Quality Index, what are the health impacts and what measures we can take to protect ourselves from the impact of harmful pollutants. We hope that you found this article helpful.

Thank you.




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