Poisoning the air we breathe

Most residents of Kathmandu are aware of the dust and smoke in the air, but few know that their masks do not protect them from the poisonous gas emissions from the capital’s ubiquitous motorcycles.

Because of the nature of their engines, two-wheeler exhausts give off carbon monoxide, nitrous oxides, and elevate the concentration of street-level ozone. Doctors say these poisonous gases have led to a worrying increase in respiratory ailments, cancers, Alzheimer’s Disease, diabetes and heart attacks.

“A few motorcycles would not be so dangerous, but there are now nearly 1 million of them on the city streets and their emission is a great public health hazard,” warns respiratory health expert Raju Pangeni at HAMS Hospital in Dhumbarahi.

Although motorcycles burn much less petrol than four-wheelers, they are up to ten times more polluting per passenger- kilometre than buses and cars. The internal combustion engine of motorcycles is also less efficient, and their exhaust systems lack catalytic converters.

Because there are fewer two-wheelers on the roads in the West, emission standards for them are more lax than for four-wheelers. However, in places like Nepal, Vietnam or Indonesia, where motorcycles outnumber cars, their cumulative emissions poison the city's air with noxious gases.

Also Read: Highway Robbery, Shreejana Shrestha

Figuring out what to do, Arnico Pande

A recent study showed that up to 2% of poorly-maintained motorcycles contributed to close to half the total pollution from two-wheelers on Kathmandu’s streets.

“The recent spike in cardio-vascular diseases in Kathmandu hospitals is partly a result of slow carbon monoxide poisoning, mainly from motorcycles,” confirms cardiologist Prakash Regmi at Bir Hospital. Residents near congested intersections in Kathmandu with thousands of motorcycles emitting gaseous pollutants are the most at risk (see map).

Ozone is the other toxic gas formed when carbon monoxide and nitrous oxides in motorcycle exhaust react in the presence of sunlight with volatile organic carbons. Large parts of Nepal have ground-level ozone in much higher concentrations than the WHO standard in the spring, as per several studies published last year in the journal Atmospheric Chemistry and Physics.

Arnico Panday, atmospheric scientist at the International Centre for Integrated Mountain Development (ICIMOD) who co-authored the papers, explains that incomplete combustion of fuel in motorcycles engines gives off carbon monoxide, volatile organic compounds like benzene, and oxides of nitrogen (NOx) which are precursor gases to ground-level ozone -- itself a highly reactive gas that can aggravate chronic respiratory diseases like asthma, bronchitis and emphysema.

Also read: Not business as usual, Nessim J Ahmad and Kaveh Zahedi

The studies showed that minor servicing of two-wheelers did not reduce gaseous pollutants much, and motorcycles were a major source of carbon monoxide in Kathmandu Valley air.

Public awareness about air pollution has grown in the past two years after suspended dust particles from road-widening and water mains laying work worsened air quality that was already thick with soot particles from diesel exhaust and garbage burning.

But only a few commuters interviewed for this article in the past week knew of invisible and odourless gases like carbon monoxide, ozone and nitrous oxides. Nine of ten motorcyclists had no idea about the poisonous gases, and blamed only dust and diesel smoke for poor air quality.

Kathmandu air pollution levels on most winter mornings are the worst in the world. The hourly Air Quality Index (AQI) from the U.S. Embassy and Phora Darbar stations which feed live into the Nepali Times website is a composite of the concentration of ozone and particles finer than 2.5 microns in the air. The daily averages in this paper (page 10) show AQI is high even during the monsoon, proving that the rains are not enough to clean the air of pollutants.

“Given that 80% of total vehicles today in Nepal are motorcycles and scooters, there should be a mechanism to monitor and control their emissions, like issuing green stickers," says BhusanTuladhar of UN-HABITAT. In the longer term, however, only an efficient public transportation service can reduce the number of motorcycles and cars on the roads.

Besides Nepal, Vietnam and Indonesia also grapple with two-wheeler congestion and poor air quality. Hanoi is banning scooters by 2030, and China now only allows electric two-wheelers.

Energy expert Manjeet Dhakal says there is no sense banning motorcycles in Kathmandu without first offering a convenient alternative: “Two wheelers are polluting and unsafe, but environment-friendly public transport policy should be implementated first.”

Moving to electric mass transit, a battery-operated Bus Rapid Transit, and offering tax incentives for electric scooters and motorcycles would be the first step. Experts say the cause of Kathmandu's air pollution is government policy that allowed unlimited vehicle imports so as to generate greater tax revenue.

“Lack of regulation on motorcycle numbers undermines the government’s own effort to promote zero-emission safa tempos and electric vehicles,” says communications officer Mona Sharma at ICIMOD. 

With local governments in place after 20 years, priority should also be on ending the monopoly of transportion syndicates so the existing public transport system is streamlined.

An already-available alternative could be electric scooters, the prices of which have dropped to Rs138,000 for some models like the Japanese Terra Echo. Chinese-made Niu M1 scooters are costlier, but are stylish and convenient.

Both have showrooms in Kathmandu. Tax rebates can bring prices down more.

Says cariolodist Prakash Regmi: “The government has to decrease the number of petrol two wheelers, provide better public transport and promote electric vehicles to ensure a healthy future for us all.”

Also read: Lost in the smog, Dewan Rai and Suvayu Dev Pant


Carbon monoxide

Carbon monoxide (CO), a colourless, odourless and tasteless gas found in vehicular exhaust, is so poisonous it is one of the commoner methods of suicide.

It is produced from incomplete combustion of fuel, and should not be mistaken for carbon dioxide (CO2) which is a gas essential for plant life while being the primary greenhouse gas warming the Earth.

Motorcycles are particularly notorious for producing CO because of the incomplete combustion in their engines. A few recreational motorcycles on the roads may not pose a danger, but when there are 800,000 motorcycles in a city like Kathmandu, it poisons the air we breathe.

“Prolonged exposure to carbon monoxide acts as a slow poison, causing various diseases of the heart,” explains cardiologist Prakash Regmi at Bir Hospital.

Human blood is red because it contains the iron-rich protein haemoglobin (Hb) in the red corpuscles which has an affinity for oxygen and carries it to various organs and tissues in the body. But haemoglobin has a 240 times greater affinity for carbon monoxide than oxygen. When Hb binds with CO, the blood cannot absorb oxygen, leading to suffocation and eventually death.

Kathmandu’s streets normally record 0.0012% CO, which will not kill people outright but can lead to cardiac and lung complications. Says respiratory expert Raju Pangeni at HAMS Hospital: “Carbon monoxide reduces the oxygen carrying capacity of the body, and can have lethal consequences.”


Carbon monoxide, volatile organic compounds and nitrous oxides in motorcycle exhaust go through complex chemical reactions in the presence of sunlight to form ground-level ozone.
This is ‘bad’ ozone, and different from ‘good’ stratospheric ozone that blocks harmful solar radiation. The ozone molecule is composed of three atoms of oxygen, unlike the oxygen we breathe which contains two atoms.

As traffic increases, bad ozone builds up during warm sunny days, harming lung functions. Kathmandu hospitals have recorded a sharp increase in patients with chronic respiratory diseases, and higher concentration of surface ozone is one of the factors.

A 2017 study published in the journal Atmospheric Chemistry and Physics measured ground-level ozone at various points in Kathmandu and found that it was highest in the day, during pre-monsoon months, and at higher altitudes on the Valley rim, exceeding the WHO standard.

Says ICIMOD atmospheric scientist Arnico Panday, who co-authored the paper: “Ozone is a growing problem in northern South Asia, and is a threat to both agriculture and human health.”

Sonia Awale


Sonia Awale is Executive Editor of Nepali Times where she also serves as the health, science and environment correspondent. She has extensively covered the climate crisis, disaster preparedness, development and public health -- looking at their political and economic interlinkages. Sonia is a graduate of public health, and has a master’s degree in journalism from the University of Hong Kong.