The Four Horsemen of the Airpocalypse

What the harbingers are of Beijing’s end of ‘clear’ days

Air pollution is found in many countries around the world. The effects on people’s health are just now being fully understood and knowing how and where pollutants are produced can contribute to crafting a solution. Liam Bates, co-founder and CEO of Kaiterra, uses the city of Beijing as a test case to examine the often hard to pin down sources of air pollution in China.


Each city’s pollutants are unique. In this article, Beijing’s pollutants are the ones being discussed. It is extremely difficult to determine the pollution source once it is in the air. If one was to read 10 studies on Chinese pollution sources, you would find they all reach different conclusions. For this reason, there is no consensus on who exactly the worst polluters are. One report says cars are the main contributor, while another says coal. While this may be a complicated subject area to explore, one can hazard a guess as to what the four main pollution contributors are in Beijing.

Motor vehicles

Cars, trucks, buses, trains, motorcycles and other gasoline powered vehicles all contribute to motor vehicle pollution. There are between five and six million cars in Beijing with most of them spending more time on the road idling than moving. Despite having a fairly well-planned transportation infrastructure, Beijing’s congestion is the main reason traffic pollution is thought to be so severe.

Why is congestion considered the main culprit behind automotive pollution? The simple answer is that having more cars on the road means more pollution, however a more complex explanation is commute time. Every car on the road lengthens the amount of time everyone spends commuting. The more time spent on the road with the car running idle, the more pollution is injected into the atmosphere.

How bad is it?

Thankfully, as of 1997, Beijing has banned the use of leaded gasoline, reducing the amount that you may
happen to breath while outside in the open air.

Particulate matter in the form of sulphates and nitrates can induce or agitate conditions like asthma or bronchitis. However, these effects on peoples’ health are well known and are not particularly unique to vehicular pollution.

The most direct effect on health, and the largest danger associated with vehicle pollution, is proximity. A factory smokestack releases a large number of harmful compounds that can adversely affect one’s health, however some of them can be broken down and disappear long before they reach the fragile alveoli. At the street level, a person is much more likely to inhale carbon monoxide, which prevents the body from carrying oxygen through the bloodstream. In high doses carbon monoxide will result in death, but most inhale low-level amounts that may result only in tiredness and cognitive issues. These more milder symptoms will clear up over time, but breathing it in every day may eventually have a cumulative effect on the body. In conclusion, most of the urban dwelling populace resides more closely to a major roadway than a factory or power plant. Due to this, car exhaust might have a much larger impact on health than what the data might suggest.

Coal combustion

President Xi Jinping has pledged to phase out the use of coal, with some optimistic reports claiming the
first coal-free day will arrive as early as 2020. The last of Beijing’s coal-fired power plants were shuttered in 2017. If analysts like Tian Miao are correct in claiming coal is “the greatest evil in the air quality game”, then
blue skies might become a common sight again in Beijing before the beginning of the next decade.

Even though Beijing stopped relying on coal, pollution blowing in from the south brings in particulate matter from newly-constructed coal plants in Hebei, as well as other coal-hungry areas like Tianjin, where plant closures have not yet been slated. Considering how long PM 2.5 can hang in the air and how far it can travel,
many are sceptical that closing the four coal-burning power stations in Beijing has had any more than a superficial effect.

How bad is it?

Burning coal is one of mankind’s most effective methods of producing air pollution. Carbon particles stay in the air for a long time and can spread easily from their point of origin. The longer these particulates remain in the atmosphere, the more likely it is for them to react with sunlight and other compounds, creating what’s called a ‘photochemical smog’. This is a major source of ozone, which can cause significant respiratory damage. Most carbon compounds aren’t particularly harmful on their own, but there are two things to consider:

1. Some fall into the ‘ultrafine’ category, meaning they are small enough to pass through your lungs and into your bloodstream; and

2. Heavy metals and pesticides easily cling to these types of particulates.

Industrial pollution

Traffic and coal pollution is fairly homogenous in its chemical composition, but industrial pollution is more complicated and unfortunately it is where the majority of ‘trace elements’ in Beijing come from.

There are a number of reasons profiling industrial pollution is more complicated than either coal or traffic emissions:

1. There are many industrial processes that pollute, and accurately testing and monitoring all of these factories are impractical.

2. Heavy industry has a hidden impact on power grid demands, resulting in a pollution increase from the large amount of electricity consumed.

3. Factories have a vested interest in alters their emissions data, hence the recent reports of more clandestine industrial practices, such as waiting until night-time to turn on smoke stacks.

What is known, is that Beijing is flanked on all sides by Hebei factories, a province that produces more steel than the entire United States. Polluting operations such as coking or cement production are large contributors. To understand the impact these projects have, one has to look no further than data showing seven out of China’s 10 most polluted cities are located relatively close to an industrial source.

How bad is it?
Most heavy metals in the air come from industrial processes. The main metals found in Beijing’s air are aluminium, potassium, calcium, titanium, iron and zinc.

All of these metals are toxic at high enough levels, and most of them are at least irritating to the respiratory tract, leading to acute cases of sore throats, wheezing, coughing, etc. Some metals, like iron, can corrode mucous membranes in the digestive and respiratory tract, leading to problems ranging from stomach ulcers and internal bleeding to pneumonia-like symptoms from diminished lung function.

Secondary aerosol particulates

Primary aerosols find their way into the air fairly regularly it can include: construction site dust, smoke from
power plants, factories and car exhaust.

Secondary aerosols are what happens when those same particles, are excited by the sun, and by interacting with one another can change their chemical state. This can mean gasses turning into particles or particles turning into gasses. There are three factors that influence the frequency of these reactions:

1. Amount of sunlight – Increased sunlight means more energy for the gas-to-particle reaction to take place.

2. The amount of time these particles spend in the atmosphere – The longer these particulates spend in the atmosphere, the more reactions that can take place.

3. Air movement – If the particulates are held static by mountains or valleys, that also determines the number of chemical reactions that happen.

How bad is it?

This is a difficult question to answer as aerosol particulates are still being researched extensively in the
scientific community. However, this chemical process is one of the main sources of ground-level ozone (which is actually a gas, not an aerosol). Even at low levels, ozone diminishes lung function, meaning that when levels are high, one is still likely to feel short of breath and have tightness in their chest.

In conclusion

Even if air pollution is a global issue, solutions must be localised. Each city’s pollution profile is unique, which also means that each city’s pollution control policy decisions must be tailored. There is no one size fits-all answer that can be applied to all regions affected by air pollution. As a result, the only way to make effective recommendations is to identify pollution at its source.

What most cities and regions have now, is a data set which does not provide enough granular information. More data is needed to provide a clear and detailed picture of what localised pollution looks like.

With the rise in affordable air quality monitoring and connected products, the goal of acquiring the right type of data is within reach.

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Liam Bates is the CEO and co-founder at Kaiterra Technology. Kaiterra is focused on developing smart devices to monitor and map air quality, both indoors and outdoors, with the goal of better understanding and thus reducing the world’s air pollution. Bates, along with his wife, recently made Forbes Magazine’s 30 Under 30. He began producing air quality monitoring devices after his wife relocated to China and developed asthma. He may be contacted at