Friday, Sep 30, 2022

Explained: As pollution peaks in Delhi, a look at pollutants you should be worried of

Delhi is once again experiencing high levels of air pollution. What are the particles found in the air, and what is their health impact?

delhi, delhi pollution, delhi air quality, delhi air pollution, delhi news, indian expressPWD workers spray water on the trees to clean the dust from leaves as air pollution rises in New Delhi. (Express Photo: Praveen Khanna)

Delhi woke up to high levels of air pollution on Friday as air quality index (AQI) slipped into ‘very poor’ category while some parts of the city saw AQI turn ‘severe’. As of 2pm, the overall AQI was 370 and eight out of 36 monitoring stations were in the ‘severe’ category, with most severely affected areas being North Delhi’s Alipur and Wazirpur, and Central Delhi’s Shadipur, which had AQI between 435 and 447.

Real-time air quality monitoring data from the Central Pollution Control Board (CPCB) showed that particulate matter of 2.5 and 10 micrometres (PM2.5, PM10) were the prominent pollutants at the three highly polluted areas.

Besides concentration of particulates, the CPCB also monitors gas concentrations, including of nitrogen dioxide (NO2), ammonia (NH3), sulphur dioxide (SO2), carbon monoxide (CO), and ozone (O3). However, concentrations of these gaseous pollutants were within the moderate range at these highly polluted areas, CPCB data shows.

What are particulates and what is their health impact?

PM2.5 and PM10 are mixture of solid and liquid particles generally having diametres of or less than 2.5 and 10 micrometres— smaller than the diametre of a single strand of average human hair, which is about 70 micrometres.

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The 24 hour exposure limit of PM2.5 in India is 60 micrograms per cubic metre air (ug/m3), while that of PM10 is 100 ug/m3. At the three highly polluted areas in Delhi between 12PM Thursday and Friday, the levels of PM2.5 and PM10 had reached 500 ug/m3 or close to it.

These particulates are emitted from various sources and can be inhaled, causing serious health problems. Their physical and chemical characteristics vary by location, and common chemical composition includes nitrates, sulfates, ammonium, and also metals and biological components. Combustion of diesel and petrol in engines, combustion of solid fuel for energy production, construction and industrial activities, and erosion of pavement by road traffic are some of the primary sources of PM, but they are also formed in the atmosphere through chemical reaction of gaseous pollutants.

Health effects of inhalable particulate matter, due to short term and long term exposure, include aggravation of respiratory and cardiovascular problems and also mortality from these problems and lung cancer, as per a World Health Organisation (WHO) report from 2013.


“For mortality, and especially as a consequence of long-term exposure, PM2.5 is a stronger risk factor than the coarse part of PM10,” states the WHO report.

“Long-term exposure to PM2.5 is associated with an increase in the long-term risk of cardiopulmonary mortality by 6–13%… Susceptible groups with pre-existing lung or heart disease, as well as elderly people and children, are particularly vulnerable. For example, exposure to PM affects lung development in children,” the WHO report states.

Explained | The various factors that cause Delhi’s air quality to dip this time of the year


A 2017 study by the India State-Level Disease Burden Initiative — a joint initiative of the Indian Council of Medical Research, Public Health Foundation of India, Institute for Health Metrics and Evaluation — found that India had one of the highest annual exposure to PM2.5 levels in the world in 2017, with highest exposure being in Delhi.

The study attributed 6.7 lakh deaths in the country to outdoor particulate matter air pollution and 4.8 lakh deaths due to household air pollution. 📣 Follow Express Explained on Telegram

What are the health effects of gaseous pollutants?

Nitrogen dioxide (NO2) gets in the air from burning of fuel, from sources including emissions from vehicles and power plants. The 24-hour exposure limit of NO2 in India is 80 ug/m3. In the three highly-polluted areas in Delhi between 12pm Thursday and Friday, minimum level of NO2 was recorded as 42 ug/m3 and maximum as157 ug/m3.

The United States Environmental Protection Agency (EPA) states that short-term exposure to high levels of NO2 can aggravate respiratory diseases like asthma, and lead to other problems such as coughing or difficulty breathing. Long-term exposure may also contribute to development of asthma and could increase susceptibility to respiratory infections.

Ammonia (NH3) is another gaseous pollutant that is monitored, whose 24-hour exposure limit is 400 ug/m3. The average 24-hour range of NH3 as of 1pm on Friday at the three highly polluted areas in Delhi was between 9 and 28 ug/m3, as per CPCB data.


The EPA states that ammonia occurs naturally in air, soil and water, and is used as an agricultural fertiliser and in cleaning products. Short-term inhalation of high levels of ammonia can cause irritation and serious burns in the mouth, lungs and eyes. Chronic exposure to airborne ammonia can increase the risk of respiratory problems, including impaired lung function.

Also read | Explained: Why Punjab’s AQI is moderate despite 11,000 stubble burning cases


Sulphur dioxide (SO2) and particulate matter emitted from combustion of fossil fuels have, historically, been the main components of air pollution in many parts of the world. A Greenpeace report from 2019 had found that India was the largest emitter of SO2 in the world due to burning of coal.

The EPA states that largest source of SO2 in atmosphere is burning of fossil fuels by power plants and other industrial facilities. Short-term exposure to SO2 can harm respiratory system, making breathing more difficult. SO2 emissions in the air can also lead to formation of other sulphur oxides (SOx), which can react with other compounds in the atmosphere and form particulate matter.


The 24-hour exposure limit to SO2 in India is 80 ug/m3 and at the three highly polluted areas in Delhi, the levels averaged at 19 to 33 ug/m3 as of 1pm on Friday. Carbon monoxide (CO) is a toxic, colourless and odourless gas, given off when fuel containing carbon, such as wood, coal and petrol, are burned. The four hour exposure limit of CO is 4 mg/m3, and 8 hour limit is 2 mg/m3.

As per the Delhi Pollution Control Committee (DPCC), the levels of CO at Alipur peaked at 3.8 mg/m3 at 10pm on Thursday and 3.4 at 8am on Friday. At Wazirpur, CO peaked at 4.4 mg/m3 at 7pm on Thursday. Data for Shadipur was not available. The US’ Centers for Disease Control and Prevention states that breathing CO can cause headache, dizziness, vomiting and nausea. If CO levels are high enough, a person may become unconscious and die. Long term exposure has been linked with increase risk of heart disease.

Ozone (O3) occurs both in the Earth’s upper atmosphere and at ground level. At ground, O3 is created by chemical reaction between oxides of nitrogen (NOx) and volatile organic compounds. The EPA states that ozone is formed when pollutants emitted by cars, power plants, refineries and other sources chemically react in presence of sunlight.

Ozone can trigger a variety of health problems, the EPA states, including chest pain, throat irritation and airway inflammation. It can also reduce lung function, harm lung tissue, worsen bronchitis, emphysema and asthma.

The 4-hour exposure limit of ozone is 180ug/m3, and 8-hour limit is 100 ug/m3. In the 24 hours as of 1pm on Friday, the range of ozone in the three highly-polluted areas of Delhi was minimum 3 ug/m3 and maximum 149 ug/m3.

First published on: 23-10-2020 at 06:56:47 pm
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