What is AQI? - Impact of Air Quality on Lung Health

What is AQI? - Impact of Air Quality on Lung Health

Air quality in Indian cities has been in an abysmal state, especially for the last 20 years. Rising air pollution is a grave concern, especially in terms of public health. Air Quality Index (AQI) is the most widely accepted standard for quantifying air pollution, globally. The values of AQI range from 0 to 500.0 refers to no air pollution and 500 is the highest level of air pollution measurable on the scale. AQI takes into account the quantity of particulate matter (PM2.5 & PM10) in the air, nitrogen dioxide, sulphur dioxide, carbon monoxide and ground level ozone. Particulate matter tends to enter the lungs and get deposited inside, causing tissue damage and inflammation. Nitrogen dioxide and sulphur dioxide trigger irritation in the mucous membranes and cause coughing, wheezing and asthma. Children, geriatric adults and people who spend a lot of time outdoors are most vulnerable to the harmful effects of air pollution.

Air quality of various Indian cities has been in the news lately, for all the wrong reasons. Of the top 30 cities with the worst air pollution in the world, India is home to 21. It has become a hot topic in recent years, due to rising concerns about air pollution and its impact on public health. Air quality is something citizens cannot escape or protect themselves from easily. Air pollution is linked to higher rates of lung cancer (especially in non-smokers), heart attacks, stroke and even premature death. In this article we will explore the most widely accepted standard for measuring air pollution, the Air Quality Index, and how to interpret its effects on lung health.

Air Quality Index (AQI) is a scale to measure the concentration of air pollutants in an area. The values of AQI range from 0 to 500. Lower values of AQI indicate better air quality, whereas higher values of AQI indicate higher levels of pollution. The Air Quality Index is calculated based on the concentration of major pollutants in the air, including particulate matter (PM2.5 and PM10), ground level ozone, carbon monoxide, sulphur dioxide and nitrogen dioxide. An AQI value of 0 to 50 is considered “Good”. AQI values from 51 to 100 are considered “Moderately Healthy”. AQI levels above 300 are considered “Dangerous”.

All the 5 major pollutants which are measured to determine AQI affect the lungs in different ways. Let us delve deeper into each pollutant’s impact on lung function:

Particulate matter refers to tiny particles suspended in the air, which can easily be inhaled. These tiny particles are not made of a specific substance; They are a complex mixture of solids, aerosols and minute droplets. The particles vary in size, shape and chemical composition. They may contain metals, elemental carbon or organic compounds. This includes pollen, emissions from burning different fuels, mold spores, dust from construction sites and landfills as well as industrial wastes. For the purpose of AQI, the particles are categorised according to their size. PM10 particles have a diameter of 10 microns or less. PM2.5 particles have a diameter of 2.5 microns or less. PM2.5 is a subset of PM10.

Airborne particles that fall under the PM10 category are easily inhaled and deposited in the lungs. PM10 is likely to get embedded on the surface of the lungs, or along the major airways of the upper lungs. PM2.5, being smaller in size, is light enough to penetrate further into the lungs than PM10. PM2.5 can get deposited in the alveoli, the tiny sacs in the lungs where oxygen exchange takes place. Particles which get deposited in the lungs cause tissue damage and inflammation. They can trigger acute bronchitis, asthma, respiratory distress, wheezing, lung cancer and premature mortality. Long-term exposure to PM2.5 has been linked to reduced lung function in children, and premature death in patients with pre-existing heart and lung diseases. Infants and older adults face the highest levels of risk.

Stratospheric ozone is desirable, because it forms a protective layer that prevents harmful ultraviolet rays from reaching the surface. Ground level ozone is not beneficial. Ground level ozone is formed when oxides of nitrogen react with volatile organic compounds (VOCs) in the presence of direct sunlight. Ground level ozone is highest in dense, urban settings but can also reach rural zones when transported by strong winds.

According to lung specialists, breathing in ozone is very harmful to the lungs. It causes asthma, particularly in children, geriatric adults and patients with pre-existing lung diseases. Children are most vulnerable because their lungs are still developing, and they are more likely to be active outside during the day. Ozone inhalation can also cause cough, sore or itchy throat, difficulty breathing, inflammation of the airways, and bronchitis. Ozone inhalation also makes the lungs more vulnerable to infections. Ozone can also cause the muscles of the airways to forcibly constrict, trapping air in the alveoli. This leads to wheezing and shortness of breath. Repeated exposure to ozone can cause long-term lung damage.

Nitrogen dioxide and sulphur dioxide are both by-products of burning fossil fuels at high temperatures. A bulk of this is contributed by the transportation and power generation industries. The highest concentration of these gases is usually found in urban centres, along roads with heavy traffic. Appliances like gas stoves can also generate nitrogen dioxide and sulphur dioxide. This can be dangerous in unventilated spaces. Nitrogen dioxide and sulphur dioxide contribute to acid rain.

High concentrations of nitrogen dioxide can cause inflammation in the airways and wheezing. It can trigger coughing and asthma attacks. Scientific evidence suggests that exposure to nitrogen dioxide causes asthma in small children. Sulphur dioxide is also known to cause irritation and inflammation in the mucous membranes of the eyes, nose, throat and lungs. It has a constricting effect on the airways, triggering chronic lung diseases with long-term exposure.

Carbon monoxide is formed when fossil fuels burn incompletely, i.e. without sufficient oxygen. It is a colourless, odourless gas emitted primarily by motor vehicles and other modes of transport. Higher levels of CO are typically found in high traffic zones and industrial zones. Wood-burning stoves, barbecue pits, bonfires and cigarettes also produce some amount of carbon monoxide.

Carbon monoxide is toxic to the body. It reduces the oxygen delivery to the tissues and vital organs in the body. Low level exposure to carbon monoxide can trigger chest pains, reduce your ability to exercise hard and make you feel short of breath. Higher levels of carbon monoxide can cause problems with vision, reduce mental acuity and makes it difficult to perform even basic tasks.

The long-term consequences of living and working in a highly polluted area are serious. Extended exposure to air pollutants can cause:

Wheezing, coughing and shortness of breath – These symptoms become very common among people living in highly polluted areas. Short term exposure to high levels of pollution can also cause this, but long term exposure makes it chronic. It becomes part of their lives even when they are healthy. Allergies are constantly triggered, weakening the immune system.

Reduced lung function – According to pulmonologists, over time, more and more particulate matter settles in the lungs and causes inflammation and tissue damage. This affects the lungs’ ability to oxygenate the blood efficiently, making the affected person tired and weak.

Chronic Respiratory diseases – High air pollution levels increase the incidence of chronic bronchitis, asthma and chronic obstructive pulmonary disease in the local population. If the person already has these conditions, it becomes exponentially worse. The rate of hospitalisations for pulmonary distress are higher in highly polluted areas.

Lung Cancer – Several studies have found a link between long term exposure to particulate matter  (especially PM2.5) and an increased risk of lung cancer. The tiny particles penetrate deep into the lungs and cause inflammation and tissue damage that could potentially lead to cancerous growths.

Premature death – Long term exposure to high levels of air pollution can shorten life expectancy, due to respiratory and cardiovascular complications. According to a 2023 study, the average life expectancy of a citizen in Delhi is shortened by almost 12 years due to air pollution.

If you’re concerned about the impact of air quality on your health, it’s crucial to consult with a healthcare professional. At Kauvery Hospital, with branches in Chennai, Hosur, Salem, Tirunelveli, and Trichy, our experienced pulmonologists are dedicated to providing comprehensive care for respiratory conditions and are equipped to address your concerns about air pollution and lung health. Prioritize your health by scheduling a consultation today.

What is the Air Quality Index (AQI)?
AQI is a scale from 0 to 500 that measures air pollution levels; lower values mean cleaner air, while higher values indicate dangerous pollution.

Which pollutants does the AQI measure?
AQI measures particulate matter (PM2.5 and PM10), ground-level ozone, carbon monoxide, nitrogen dioxide, and sulphur dioxide.

How do PM2.5 and PM10 affect lung health?
These tiny particles can be inhaled into the lungs, causing inflammation, tissue damage, and increasing the risk of respiratory diseases.

What impact does ground-level ozone have on the lungs?
Ozone irritates the airways, can trigger asthma attacks, and may cause long-term lung damage with repeated exposure.

What are the long-term effects of high air pollution on the lungs?
Prolonged exposure can lead to chronic respiratory issues, reduced lung function, an increased risk of lung cancer, and even premature death.

Who is most at risk from poor air quality?
Children, older adults, and those who spend a lot of time outdoors are especially vulnerable to the harmful effects of air pollution.

Kauvery Hospital is globally known for its multidisciplinary services at all its Centers of Excellence, and for its comprehensive, Avant-Grade technology, especially in diagnostics and remedial care in heart diseases, transplantation, vascular and neurosciences medicine. Located in the heart of Trichy (Tennur, Royal Road and Alexandria Road (Cantonment), Chennai (Alwarpet & Vadapalani), Hosur, Salem, Tirunelveli and Bengaluru, the hospital also renders adult and pediatric trauma care.

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