Why Is Air Pollution Worse During Winter?
Last updated August 6, 2019

Air pollution during winter

Air pollution is actually worse during winter. So it’s puzzling why many people still believe that it peaks in summer. Of course, if you have ever lived in a hot and overcrowded capital, and endured a suffocating commute, you could be forgiven for thinking so. You emerge from a sweltering metro, barely able to breathe, into a sun-baked concrete jungle. Somehow all smells are more pungent in the summer, everything from rubbish through to the whiff of döner kebabs.

Perhaps you also believe that summer air quality is worse because of the longer days and ultraviolet radiation. The stable weather means that, without a storm, city air can seem stagnant and airless.

Temperature inversion in winter

In winter, a confluence of natural phenomena exacerbates air pollution. Overcast weather, in particular, tends to trap the pollution beneath the cloud. In this kind of temperature inversion, the warm air acts as a lid, covering air pollutants. 

Air temperature usually falls along with increased elevation. But sometimes during the night, and more often during cold nights, there is a warm layer of air between the layers of cooler air. This is called temperature inversion. Here we will explain the origin of the following 3 types of temperature inversion connected to air pollution. They are as follows:

1. Surface inversion
2. Subsidence inversion
3. Frontal inversion

1. Surface inversion usually occurs during cold and windless nights. During cold winter nights, the earth surface loses temperature very fast. The air close to the surface gets cooler faster than the air above it. This is how the warmer layer of air, above the colder one, comes to be formed.

2. Subsidence inversion occurs around high-pressure centres when a large air mass moves downward. And if it continues further down near the ground then this air close to the surface becomes colder than the air above it. Subsidence inversion is more often seen near subtropical oceans and the Nordic continents because they are located in high-pressure centres.
3. Frontal inversion happens on the borders of hot and cold fronts. The cold air mass is denser and pushes the hot air above it. Thus the lighter hot air stays above the cold and denser one and this is how this phenomenon occurs.

So what is the correlation between temperature inversion and air quality? Warm layers prevent the air below it passing through. Thus, pollutants from household heating, vehicle exhausts, and other industrial pollutants circulate near the surface. The concentration of toxins in the air we breathe increases and we get stuck in a “Large Dome” as depicted in the Simpsons Movie.
A city located in a valley and close to a mountain is more liable to experience temperature inversion than other cities. The cold air is denser and heavier; therefore it often slides down the mountain slope and ends up in a valley, leaving the warmer air above.

So, in reality, winter air is actually worse. If you suffer from asthma or congestive problems then you should pray for storms – rain or snow – popularly known as ‘scrubbers’, to clear the air. Otherwise, especially in Asia, excessive quantities of harmful components – lead, zinc and polycyclic aromatic hydrocarbons – contaminate the air. So winter air pollution definitely aggravates breathing problems. The temperature inversion is one of the main reasons why the AQI usually registers red, purple, and even brown, in winter. 

The winter cold means more fossil fuels are burnt

Read more: What are the causes of air pollution?

While industrial pollution is at constant levels throughout the year, household heating and emissions from the vehicles are getting higher during the colder days of the winter. Especially in lower income countries where is likely to burn garbage and coal for heating the levels of PM2.5, carbon monoxide and other toxins increase significantly.

For the last decades, the central heating in China was mainly powered by coal. The increase of toxins in the air combined with the temperature inversion creates the smog that we breathe every winter.

Asian cities are the worst winter polluters

If you really doubt that air pollution is worse during winter, however, then visit a Chinese city in January. If you’re a masochist and enjoy wheezing your way through thick smog, you will have fun. Not only is the air dense and grey, it’s also stuffed full of PM 2.5 particles, small enough to penetrate deep into the bloodstream and cause real damage. So much so that the authorities in Beijing, for example, have issued red alert warnings.

Data clearly shows the peaks of air pollution in winter



India is another heinous offender.  Crop burning during the winter is also an interesting phenomenon in India. Delhi’s pollution levels recently rose to between 12 to 19 times the permissible limit during winter hours. The city’s nine million vehicles make the atmosphere even more unbearable. Life in India’s capital has even been likened to living in a gas chamber.  In November 2017, one of the most dangerous air particles, known as PM 2.5, reached more than 700 micrograms per cubic meter in certain areas of Delhi. Experts claim that prolonged exposure to this is equivalent to smoking more than 40 cigarettes a day. Small wonder then that few of the city residents have healthy lungs.[1]

Urgent action is clearly required in Delhi to curb congestion, primarily by encouraging public transport. Experts reckon that the city needs between 12,000 and 15,000 buses but its current fleet numbers just 5,000. Polluting vehicles also need to be taxed more heavily.

Are Things Getting Better?

Sadly, European cities offer little respite. Last year, Paris suffered its worst, and longest, winter for a decade. The authorities in the French capital, in a bid to combat the problem, imposed a so-called half traffic measure whereby vehicles with odd number plates were allowed into the city on alternate days.[2]

Britain recently decided to ban all new petrol and diesel vehicles from 2040 onwards in a bid to curb rising levels of nitrogen oxide. But is it a case of too little, too late? Air pollution both inside and outside the home causes at least 40,000 deaths a year in the UK, according to a recent report from the Royal College of Physicians and the Royal College of Paediatrics and Child Health.[3] Over several days last January, London’s air quality was judged inferior to Beijing’s. Readings from the air quality index showed that particulate matter was concentrated at 197 micrograms per cubic metre in the British capital, as opposed to 190 in Beijing.[4]

If it’s any consolation to Brits, things used to be even worse. Aficionados of old movies depicting Victorian London will be familiar with the look of the aptly named ‘Big Smoke’ in winter. It’s amazing that Jack the Ripper could see who he was strangling since city dwellers could barely see barely more than a few metres ahead!

Back then most of London’s air pollution was caused by the burning of huge quantities of domestic and industrial coal. With the onset of natural gas, as well as more stringent air quality targets imposed by governments, such ‘smoggy’ episodes have dwindled but most definitely not eliminated, mainly because of the proliferation of road transport.

Soaring Energy Demands

Our love affair with the motor car has continued despite it contributing to alarming levels of pollution. Moreover, a study by the American Journal of Respiratory and Critical Care Medicine has shown that smog in Europe and North America could be more than 25 times more lethal than the average air pollution in Chinese cities.

The situation seems to be worsening worldwide. And winter is definitely the worst time. Why is this? Demand for energy soars as it gets colder, accompanied by more burning of coal and other fossil fuels. In Indian cities, for example, people burn more biomass to heat their homes. The end of the harvest season also means that farmers burn the stubble off their fields. Throughout the northern hemisphere, more smoke emanates from fireplaces and wood burners. Add to this too many idle cars poisoning the atmosphere with carbon dioxide and you have a toxic mix.

How to improve air quality

Environmentally-friendly measures are sorely needed. Recently, Italy’s economic minister confirmed that his country is committed to phasing out coal towards complete cessation by 2025. Italy now joins France, the UK, and Canada in pledging to end coal-burning. A step, at least, in the right direction.

Another ‘solution’ that would greatly improve the atmosphere is a switch to electric or hybrid cars. Obviously, limiting the volume of traffic and imposing congestion charge would also help.

Areeba Hamid, an air pollution campaigner with environmental group Greenpeace, has especially sharp words for car manufacturers. “We now know fumes from diesel vehicles are a lot more toxic than car companies claimed and this is a big cause of air pollution in Europe and North America.”

The right measures from above

Read More : Running away from air pollution.

It is up to the authorities to implement clear directives that set the right anti-polluting agenda. In Beijing, for example, it was recently announced that all construction of road and water projects, as well as demolition of housing, will be halted in the winter.

Without more orchestrated government action – like that imposed by the Chinese authorities – we can only rely on individuals making sensible lifestyle choices. And that means the sight of urban commuters spluttering their way through the winter is unlikely to disappear.

Find out our solutions for protection against air pollution

Written By airlief

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1 Comment

  1. Hi I’m a physics teacher in Iran.
    Air pollution in Tehran is very severe.
    My students and I need information about the temperature inversion at a certain height.
    Tehran is about 1,400 meters above sea level. The cold air layer above the polluted air is approximately a few meters. At what height does this layer usually start? How can we measure it?
    Thanks and best wishes to you

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