Air quality in Phnom Penh

Is Phnom Penh a city with polluted air?

Phnom Penh is a city located in Cambodia, being the capital as well as the most populous city in the country. The name translates to Penh’s hill, something alluding to the story behind the city’s creation, and has been known under other names such as Krong Chaktomuk in times past. It is a major commercial, economic and touristic hub, with visitors coming from all over the world, mainly to Phnom Penh as well as Siem Reap, the home of Angkor Wat temple. Whilst this is great for the economy, with a large amount of visitors coming from both the western world as well as Asia, in particular China in recent years, it has the negative side effect of driving pollution levels up, with an increase in vehicle usage as well as the subsequent property and hotel boom to support an ever growing influx of tourists as well as expatriates coming to Phnom Penh to live and work.

Looking at the cities PM2.5 levels taken over the course of 2019, Phnom Penh came in with an average yearly reading of 21.1 μg/m³. This reading put Phnom Penh into the ‘moderate’ pollution bracket, one which requires a PM2.5 reading of anywhere between 12.1 to 35.4 μg/m³ to be classified as such. This shows that whilst Phnom Penh does not have an overtly bad level of air pollution, it could still stand to improve its air quality, coming in at 818^th place out of all cities ranked worldwide. Certain months of the year were seen to have jumped above the yearly average (as well as some coming in considerably cleaner), and as such, Phnom Penh fits the title of its rating as indeed subject to moderate year round levels of pollution.

What are the main causes of pollution in Phnom Penh?

With a large and growing population within its city limits, a majority of Phnom Penh’s pollution would come from the subsequent rise in vehicles. Many people from provincial areas have migrated towards the capital over the last decade, as well as the city itself growing at an incredibly fast rate, with huge amounts of development taking place that are propelling the city forward in its economic growth.

So as such, the numerous personal vehicles on the road such as cars and motorbikes would be responsible for large buildups of pollution, particularly prominent because Phnom Penh does not experience that much rainfall for most of the year to aid in washing away air contaminants. Other sources of pollution would be the numerous construction sites and road repairs happening throughout the city, with large unattended piles of sand and finely ground gravel responsible for leaking a heavy amount of PM10 and PM2.5 into the air, along with other chemical pollutants, which will be discussed in short.

Other sources would include emissions from factories, much of which would run on coal and other fossil fuels, as well as the occasional open burning of refuse and other organic material, although in recent years there has been a drastic reduction in the open burning of waste material in the streets.

When is pollution at its worst in Phnom Penh?

Observing the data taken over the course of 2019, there emerges a clear pattern as to when the air quality is at its best and also when it is at its worst, going by the PM2.5 levels on record. It becomes apparent that air quality levels start to decline around November, with the previous months reading of 16.9 μg/m³ taken in October jumping up considerably to 27.2 μg/m³ in November. This then goes up even further and hits 31.1 μg/m³ in December. These elevated months of pollution continue on into the next year, with the months of January through to April also showing raised levels of PM2.5.

These readings in the early portion of the year were 29 μg/m³ in January, and then in following, 29.9 μg/m³, 33.2 μg/m³ and 23.9 μg/m³ in April. This indicates that March was the most polluted month of the year in 2019 at 33.2 μg/m³, being only a few units away from moving up into the ‘unhealthy for sensitive groups bracket’, a rating which requires a PM2.5 reading of anywhere between 35.5 to 55.4 μg/m³. So, in closing, Phnom Penh sees its worst levels of pollution starting around November and then continuing into April of the following year, before it starts to show a considerable improvement in the following months.

When is the air quality cleanest in Phnom Penh?

Following directly on from the previous question, as mentioned the levels of air pollution started to abate in April through to the following month. April 2019 came in with a PM2.5 reading of 23.9 μg/m³, followed by a significant drop to 17.7 μg/m³ in May, and then an even further drop to 12.5 μg/m³ in June. The following months showed the best levels of air quality, with one month even going down into the ‘good’ ratings, which requires a PM2.5 reading between 10 to 12 μg/m³ for classification, a very fine margin of entry and only a few units away from meeting the World Health Organizations (WHO's) target goal of 10 μg/m³ or less for the most optimal quality of air (with the closest to 0 μg/m³ of course being the ultimate target).

To continue, the months of June through to August all came in with best readings, with 12.5 μg/m³, 12.8 and 10.2 μg/m³ all having been recorded respectively. September and October also saw decent air quality ratings, although they were already showing signs of starting to rise again, with readings of 14.5 μg/m³ and 16.9 μg/m³. It is after October that Phnom Penh’s pollution levels took the leap back up again, as touched on in the previous question. In summary, the months of May through to October had the best quality of air in Phnom Penh.

What are some of the main pollutants found in the air in Phnom Penh?

With much of its pollution arising from vehicular usage, as well as pollution released from factories and construction sites, the chemical compounds and particulate matter in the air would consist mainly of ones such as nitrogen dioxide (NO₂) and sulfur dioxide (SO₂), with nitrogen dioxide being the chief offender when it comes to vehicle emissions.

Others include finely ground silica and gravel dust, along with black carbon being released from open burn sites, vehicle exhaust and factories. Both black carbon and silica dust are known carcinogens, representing hazards to people’s health, alongside other pollutants known as volatile organic compounds (VOC's) which include chemicals such as benzene, methylene chloride and xylene.