Nitrogen dioxide: a major pollutant in Bengaluru

Nitrogen dioxide: a major pollutant in Bengaluru

Vehicular pollution in Bengaluru. (Photo by Tejas Dayananda Sagar)

By Kapil Kajal
While carbon dioxide and particulate matter stay in the limelight for increasing the air pollution levels, nitrogen dioxide escapes mainstream attention.  NO2 is responsible for the reddish-brown hue of smog and is a poisonous gas, which mixes with air pollutants to create ozone and gives rise to several respiratory ailments such as asthma. The increasing levels of NO2 in Bengaluru has alarmed experts, who attribute the traffic and waste mismanagement as the primary cause behind the rise.

Dr TV Ramachandra, a professor with the Centre for Ecological Sciences at the Indian Institute of Sciences (IISc), mentioned that NO2 in Bengaluru is produced by vehicles, burning of waste, agricultural soil management and industrial waste. 

According to an IISc titled 'Greenhouse gases footprint of major cities in India' published in 2015, NO2 emission from soil management, municipal solid waste, domestic wastewater, and industrial wastewater plays a huge role in adding greenhouse gases to the environment in Bengaluru. 

Dr H Lokeshwari, Chief Scientific Officer with the Karnataka State Pollution Control Board (KSPCB), stated that the increase in nitrogen dioxide is because of the combustion of fuel by vehicles. To reduce the level of particulate matter and nitrogen dioxide, the government is adopting Bharat Stage VI (BS-VI) emissions standards from April 2020, she added.

Experts point out that the global warming potential (GWP), a measure of how much heat a greenhouse gas traps in the atmosphere relative to carbon dioxide, of NO2 is high and that the administration should take steps to manage it.

Nitrogen dioxide is 298 times more harmful than carbon dioxide, Dr Ramachandra noted.

Bengaluru second in NOx emissions

A study titled 'Emission from India’s transport sector: Statewise Synthesis' published by IISc in 2016 stated that Bengaluru is the second most polluted city in terms of oxides of nitrogen (NOx) emission after Chennai.

Emission from India’s transport sector in major cities of India, Chart- IISc

The data on NO2 emissions from the Continuous Ambient Air Quality Monitoring Stations installed by the KSPCB in Bengaluru state that the emission until June 2018 was 35 µg/m3 (1 g=10 lakh µg) and in 2019, it increased to 43. The average emission in 2017 was 31.5 µg/m3. The World Health Organization (WHO) set a guideline value of 40 µg/m3 (annual mean) for nitrogen dioxide to protect the public from its harmful effects.



Excessive ozone in the air can have a marked effect on human health. It can cause breathing problems, trigger asthma, reduce lung function and cause lung diseases.

According to the WHO, the pollutants with the strongest evidence for public health concern include particulate matter (PM), ozone (O3), nitrogen dioxide (NO2) and sulphur dioxide (SO2).

“In children and adults, both short- and long-term exposure to ambient air pollution can lead to reduced lung function, respiratory infections and aggravated asthma. Maternal exposure to ambient air pollution is associated with adverse birth outcomes, such as low birth weight, pre-term birth and small gestational age births. Emerging evidence also suggests ambient air pollution may affect diabetes and neurological development in children,” WHO mentioned while warning against the effect of outdoor air pollution.

Dr Yellapa Reddy, the Governing Council Member of the Foundation for Ecological Security of India, highlighted that vehicular emission is the primary cause of the production of nitrogen dioxide.

He explained that when diesel and petrol burn, they release unburnt hydrocarbons. In the ideal running, 20 to 30% unburnt hydrocarbons and oxides of nitrogen are released, he added. 

When these hydrocarbons, oxides of nitrogen and sunlight interact, they release a secondary pollutant (primary being nitrogen dioxide) named Ground-Level Ozone (O3), which is a deadly secondary pollutant, he informed. 

He added that the byproducts of the reactions have adverse effects not only on the human body but also plants and animals. Even the fertilisation of plant comes to halt.

To address this issue, he stated that the roads and signals should be synchronised with a focus to reduce the traffic and the number of vehicles on the road. “If one vehicle stops at a signal, it increases its ideal running time increases, which results in the emission of pollutants,” he highlighted.

(Author is Mumbai - based freelance writer and a member of, a pan-India network of grassroots reporters.)

Get a round-up of the day's top stories in your inbox

Check out all newsletters

Get a round-up of the day's top stories in your inbox