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How bad are the air pollution levels in Tehran?

Tehran is the capital city of Iran. It has some 8.7 million inhabitants, making it one of the most populous cities in Iran as well as the whole of west Asia. The levels of pollution in Tehran are a topic of great importance for its citizens, with large quantities of smoke and dust filling Tehran each year, so much so to the point that the country is considering moving the capital to another location (with other attributable factors such as earthquakes also playing a part in this decision, which has yet to see any progress since its announcement in 2010).

There are a number of reasons for Tehran's pollution levels, with some lying in the industrial sector, vehicular sector as well as its geography, with the sizeable Alborz mountain range to the north of the city contributing to its pollution readings, due to allowing smoke and dust to accumulate and not disperse properly due to lack of wind being trapped in a ‘pollution sink’.

In 2019, Tehran came in with a PM2.5 reading of 25.9 μg/m³, putting it into the moderate pollution bracket. This rating requires a PM2.5 reading of anywhere between 12.1 to 35.4 μg/m³ to be classed as such. Despite the title, moderate levels of pollution can still be extremely harmful to its citizens or anyone who breathes it, whether it is on a long or short-term basis. Tehran frequently came in year-round with similar moderate readings, showing elevations in its pollution levels towards the end of the year, where numbers rose as high as 43.9 μg/m³ in November.

The 2019 average reading of 25.9 μg/m³ was enough to put Tehran into the 582^nd place out of all polluted cities ranked worldwide, with the country of Iran itself actually coming in at 27^th place out of all countries ranked worldwide. This shows that whilst Tehran certainly has its own pollution problems to deal with, there are other cities in the country that came in with worse year-round readings than the capital.

What are the main causes of pollution in Tehran?

The main causes of pollution in Tehran stem from a few sources, and are then compounded by its geographical location and topography, as well as meteorological conditions playing a role. A large amount of the pollution comes directly from vehicle usage, along with substandard and poor-quality fuels being used in them. Without delving too deeply into the geo-political reasons behind this, international sanctions have led to refineries in Iran being allowed to manufacture fuel that is of lesser quality that many international fuels would be.

With the fuel factor in mind, it is known that many of the cars that inhabit the roads are often old and fall well below what would acceptable for emission standards. This issue, coupled with the fuel one, and then added together with a large over-reliance on personal vehicles in the city has led to large amounts of smoke and haze being produced by the automobile industry. Lastly there are a large number of factories and industrial areas bordering Tehran's city limits, many of which would be running on fossil fuels for their heavy machinery, causing further elevations to the year-round ambient pollution levels.

Has pollution in Tehran gotten worse?

Looking back at the data taken over the last few years, it can be seen that pollution levels in Tehran have remained fairly consistent, all staying within the ‘moderate’ pollution rating bracket. However, gradual improvements have been made in the PM2.5 readings. PM2.5 refers to fine particulate matter of 2.5 micrometers (or less) in diameter. Due to its incredibly small size, it has a host of issues for those who respire it, and as such it is used as a major factor when calculating the overall level of air quality.

Observing the data, in 2017, Tehran came in with a PM2.5 reading of 34 μg/m³. This put it at the higher end of the moderate pollution bracket, and with an increase of only just 1.5 units it would move up into the higher bracket of ‘unhealthy for sensitive groups’, a rating that as the name implies would have a large number of negative effects on vulnerable portions of the population.

When is pollution in Tehran at its worst?

Once again looking at the data, it can be seen that pollution levels reach a peak towards the end of the year. This is when large amounts of smoke, haze and fumes would all be permeating the atmosphere, causing the elevated readings and being a noticeable concern for its citizens.

The cleanest month observed was April, with a PM2.5 reading of 13 μg/m³, making it only 1 unit away from moving down into the ‘good’ air quality bracket, which requires a reading of 10 to 12 μg/m³ to be classed as such.

This number however did not stay within that level for long, rising slowly till it reached its peak in November, although of note is that the months of June through to October, the pollution levels stayed very much at the same level, all hovering around the mid 20’s in terms of PM2.5 readings.

Whilst this is not a desirable number by any means, it is certainly more optimal than the end of the year, with November coming in at 43.9 μg/m³, and December at 41.1 μg/m³. These levels of pollution mean that those suffering from compromised immune systems, the young children or elderly, or those sensitive to chemical pollutants would find themselves at risk, and would find solace in preventative measures such as the wearing of particle filtering masks and avoiding outdoor activities whenever possible.

What are some health risks associated with breathing polluted air in Tehran?

Some of the health risks associated with breathing elevated levels of pollution, such as the ones seen at the end of the year (although with its year-round high readings these health risks would still be fairly prominent), would be ones mainly affecting the respiratory, cardiovascular and circulatory systems.

With large amounts of PM2.5 and PM10 coming from dust sources as well as emissions from fossil fuel-based vehicles and factories, damage to the lungs can occur in the form of lung tissue scarring, leading to a reduction in their full function as well as increased susceptibility to respiratory diseases such as pneumonia, bronchitis and asthma.

With larger particles on PM10 in the air, irritation to the eyes, nose, throat and skin can occur, along with increased risks of lung cancer. These are but a few of the health risks associated with breathing polluted air in Iran's capital city.