Qualité de l’air à Hotan

Is the air badly polluted in Hotan?

Hotan is a city located in the far western region of China. It is home to over 408 thousand people as per a census conducted in 2018, and will have thus grown since then. It is also a city that has seen some of the worst air pollution levels in recent times, coming in with some catastrophic readings of pollution levels that placed it within the highest position of all cities worldwide.

In the month of April of 2021, Hotan was seen with a US AQI reading of 122, a number that would place it within the ‘unhealthy for sensitive groups’ bracket for that particular point in time. As the name implies, many people in the city would be at great risk for adverse health effects occurring, with more vulnerable groups such as those with poor health or compromised immune systems being even more at risk, along with children, the elderly and pregnant women.

This however pales in comparison to its reading in the year prior, when the city came in with a PM2.5 reading of 110.2 μg/m³ as its yearly average, placing it in 1st place out of all cities ranked in China, as well as all 1st place out of all cities ranked worldwide in 2020. This is indicative that the air quality in Hotan would shorten the lifespan of its citizens by a significant amount, with the PM2.5 count of 110.2 μg/m³ placing it in the higher end of the ‘unhealthy’ ratings bracket, which requires a PM2.5 reading of 55.5 to 150.4 μg/m³ to be classified as such.

PM2.5 refers to particulate matter that is 2.5 micrometers or less in diameter, being comprised of many different types of coagulated chemicals or other such materials. Due to its immensely small size and the danger it presents to human health, it is used as one of the major components in calculating the overall US AQI, or United States Air Quality Index, a number that is a composite of a number of different pollutants including PM2.5, PM10 and various other compounds that will be discussed in more detail later.

In regards to the extremely poor air quality seen in Hotan, much of it is heavily linked to the large amounts of both fine (PM2.5) and coarse (PM10) particles that are blown up into the air from the frequent sandstorms, made worse by the addition of various industrial and anthropogenic activities that also cause large amounts of pollution to permeate the atmosphere.

What causes such high pollution levels in Hotan?

Hotan has many pollutive issues similar to other cities in China, with an unprecedented increase in industry taking its toll on the quality of the air. With many industrial sites and factories rapidly opening up, there is a subsequent increase in the amount of chemical contaminants and dangerous particulate matter appearing in the air.

Vehicles would also play a large role in pollution levels, with many of them being aged or out of date, as well as running on unclean fuel sources due to lack of stringent regulations. Freight vehicles such as lorries or trucks that move in and out of the city for industrial purposes also add to this element, with even the tires of such vehicles giving off thousands of tons of microscopic rubber particles that can build up in the air.

However, for Hotan, the main problem appears to be coming from the fervent dust storms that are so frequent in the region, with April through to June being the official ‘season’ for dust clouds, although of note is that they can strike at any time of the year without warning. Hotan finds itself near the Taklamakan desert, and with many cities nearby in Xinjiang, these sandstorms can appear spontaneously and cause visibility to drop to less than 100 meters in very short spans of time.

These huge clouds of both fine and coarse particles make the air extremely polluted and dangerous to breathe, with these materials having many damaging effects to both the lungs and other systems in the body. Scarring of the lung tissue can occur which can lead to many ill health effects, as well as the tiniest particles having the ability to even enter the bloodstream and wreak further havoc on the various systems throughout the body.

When is the air pollution level at its highest in Hotan?

Observing the data collected over the course of 2020, there were some months with the most extreme levels of PM2.5, as would be expected from a city that took first place out of every city ranked worldwide. To quote some of these figures, the months of February through to April were when the pollution levels hit their absolute peaks, with PM2.5 numbers of 124.7 μg/m³, 264.4 μg/m³ and 176.4 μg/m³ coming in respectively.

This made March the most polluted month of the year, with a PM2.5 reading that placed it in the ‘hazardous’ air quality bracket, a rarely seen rating that indicates that the air would be directly linked to many early deaths and extreme health issues as a result. To fall into the hazardous bracket, a reading of any PM2.5 number greater than 250.4 μg/m³ is required, the highest ranking of air pollution available.

When is the air quality at its least polluted in Hotan?

Whilst every month had extremely high readings of air pollution, the months of January, July, August, November and December all came in with slightly more appreciable readings, with PM2.5 numbers of 93.7 μg/m³, 85.2 μg/m³, 84 μg/m³, 59.7 μg/m³ and 51.9 μg/m³ all being present respectively, making December the cleanest month of the year and the only month to make it into the ‘moderate’ pollution bracket, eking its way in by just a few units, albeit on the absolute high end of this ratings bracket.

What are the different types of pollution that can be found in Hotan’s air?

With much of its pollution stemming from natural occurrences and compounded further by anthropogenic activity, Hotan would have large amounts of the aforementioned coarse and fine particles present in the air, as well as a variety of different chemical pollutants. Finely ground silica, sand, gravel and various other types of dust would be present, some of which (such as silica and black carbon) having carcinogenic properties when inhaled.

Other pollutants released from various industrial or vehicular sources would be ones such as ozone (O₃), nitrogen dioxide (NO₂) and sulfur dioxide (SO₂), as well as volatile organic compounds (VOCs), dioxins, furans and even heavy metals such as mercury, lead and cadmium.