Nitrogen Dioxide Pollution

Nitrogen Dioxide Pollution

Context: The surge in nitrogen dioxide levels witnessed in certain areas of Delhi might be attributed to the increased Diwali-related traffic, exacerbating the city’s air pollution challenges. The recorded levels were four times higher than the National Ambient Air Quality Standards recommended 24-hour limit and exceeded the World Health Organisation’s guidelines by over 13 times.

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More about the news:

  • In South Delhi, the Delhi Pollution Control Committee’s data reveals a concerning NO2 level of 329.7 µg/m3 at 5 pm. To put this in perspective, the national 24-hour standard is 80 µg/m3, while the WHO recommends a stricter guideline of 25 µg/m3.
  • Despite the implementation of all four stages of the Graded Response Action Plan (GRAP) in Delhi, including restrictions on transport like a ban on diesel medium and heavy goods vehicles, NO2 levels remain high.
  • TERI and the Automotive Research Association of India’s 2018 emissions inventory indicates that the transport sector is a major contributor, accounting for 81% of NOx emissions among local sources in Delhi.
  • The National Capital Region faces NOx from various sources, including power plants, diesel generators, and industries.
  • During this period, pollutant spikes, including gases like nitrogen dioxide, can occur due to the trapping of pollutants in cool, calm conditions. 

What is Nitrogen Dioxide?

  • Nitrogen dioxide, or NO2, belongs to the nitrogen oxides (NOx) group—a collection of gases formed when fossil fuels like coal, oil, natural gas, or diesel undergo combustion at high temperatures.
  • Existing as a gas at ambient temperatures, nitrogen dioxide is acidic, corrosive, and possesses strong oxidizing properties.
  • Recognized for its pungent odour, NO2, along with fine particulate matter, contributes to the characteristic reddish-brown haze associated with smog. 
  • This reactive gas plays a key role in the creation of various air pollutants such as ozone (O3), nitric acid (HNO3), and nitrate (NO3-) particles, all generated through photochemical reactions.

Sources of Nitrogen Dioxide Emissions: 

  • The main sources of NO2 emissions are trucks, buses, and cars, and there are additional contributions from diesel-powered non-road equipment, industrial processes (such as oil and gas production, industrial boilers, and mobile engines), coal-fired power plants, and even food processing industries.
  • Nitrogen dioxide isn’t typically emitted directly into the air; instead, it forms when nitrogen oxide (NO) and other nitrogen oxides (NOx) react with other airborne chemicals.
  • Notably, burning natural gas (methane), both outdoors (e.g., gas-fired power plants) and indoors (e.g., stoves, dryers, space heaters), produces NO2.
  • Natural sources, like volcanoes and bacteria, also release nitrogen oxides.

Environmental Effects:

  • Nitrogen dioxide, even at short-term concentrations of 120 µg/m3, proves toxic to plants, hindering their growth. When coupled with sulphur dioxide and ozone, the adverse effects intensify, potentially leading to acid rain formation.
  • NO2 also directly absorbs shorter blue wavelengths of visible light, contributing to visibility reduction, and indirectly contributes to nitrate aerosol haze formation (brownish hue/summer smog). 
  • In the presence of moisture, nitrogen dioxide forms corrosive acids, impacting building materials at elevated concentrations.
  • Indoor Pollution:
  • Indoor NO2 levels are predominantly influenced by NO2-emitting appliances, indoor-outdoor air exchange rates (such as open or closed windows), and seasonal variations.
  • Common indoor sources of NO2 emissions include gas stoves and space heaters and improperly vented furnaces, water heaters, and clothes dryers are additional potential sources.

Health Effects of Nitrogen Dioxide Pollution:

  • Nitrogen dioxide induces various adverse effects on lung health, including heightened inflammation and exacerbated cough and wheezing.
  • Scientific evidence also suggests a potential link between NO2 exposure and the development of asthma in children. 
  • In a comprehensive 2022 review, multiple studies indicated a strong association between elevated NO2 levels, increased particulate matter, sulphur dioxide, and detrimental impacts on heart and lung health. These pollutants were also found to affect pregnancy and birth outcomes, posing a likely risk of kidney and neurological harm, autoimmune disorders, and cancer.
  • AIIMS Study on NO2 Pollution:
  • A study conducted by AIIMS, Delhi, revealed that exposure to nitrogen dioxide (NO2), even over a short duration ranging from zero to seven days, led to a staggering 53% increase in emergency room visits.
  • This finding is particularly alarming as it surpasses the impact of the more familiar pollutant PM 2.5, which increased patient load by 19.5%.
  • Notably, the study observed a higher rate of admissions among individuals with co-existing health conditions rather than solely respiratory illnesses.

WHO Air quality guidelines:

  • The Air Quality Guidelines (AQG) established by the World Health Organization (WHO) serve as a global benchmark, guiding national, regional, and city governments in their efforts to enhance the health of their citizens by mitigating air pollution.
  • WHO consistently integrates scientific evidence on the health impacts of air pollution and monitors the progress of countries in improving air quality.
  • In 2021, WHO released a revised Global Air Quality Guidelines announcing more stringent limits for six pollutant categories – particulate matter (PM), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2) and carbon monoxide (CO). 
  • The guidelines set the stage for eventual shifts in policy in the government towards evolving newer stricter local and national air quality standards and will help countries in protecting health as well as mitigating global climate change.

Recommended 2021 AQG levels compared to 2005 air quality guidelines: 

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(Follow the link to read India government initiatives to deal with air pollution:

Prelims Previous Year Questions:

Q. Consider the following: (2022)

1. Carbon monoxide

2. Nitrogen oxide

3. Ozone

4. Sulphur dioxide

Excess of which of the above in the environment is/are cause(s) of acid rain?

(a) 1, 2 and 3

(b) 2 and 4 only

(c) 4 only

(d) 1, 3 and 4

Answer: (b)

Q. Consider the following statements: (2020)

1. Coal ash contains arsenic, lead and mercury.

2. Coal-fired power plants release sulphur dioxide and oxides of nitrogen into the environment.

3. High ash content is observed in Indian coal.

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 and 3 only

(c) 3 only

(d) 1, 2 and 3

Answer: (d)

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