Why is Bangkok’s air so bad? This study breaks down the complicated answer – and way forward.

Road traffic is indeed responsible for most of Bangkok’s seasonal air pollution, but a new study concludes that other sources such as field burning and factory emissions – as well as natural phenomena – play decisive roles that can’t be ignored.

Rocket Media Lab analyzed the data from last year’s most polluted month to determine that combustion engines in cars, trucks, tuk-tuks, and other vehicles accounted for 72% of the hazardous fine particulates known as PM2.5 during April 2022, followed by factories (17%) and field burning (5%).

A key finding is that not any one factor determines whether Bangkok will spend the day gasping. Rather, multiple, related circumstances can make the difference between breathing a little haze and orange soup.

The study examined data from sources including Greenpeace Thailand, the World Air Quality Index Project, City Hall, and the Geo-Informatics and Space Technology Development Agency in a bid to definitively explain the source of the pollution and also offer some policy prescriptions.

Pollution was a factor in more than 32,200 premature deaths in Thailand in 2019, the most recent year tracked by the WHO’s State of Global Air.

Tip of the smogberg

In April 2022, when the concentration of PM2.5 was four times higher than World Health Organization guidelines, the majority of the air pollution was generated by fossil fuel combustion.

But that doesn’t explain why the pollution only shrouds the capital in certain months, when the number of vehicles on the road hasn’t changed.

“The number of cars in Bangkok is not significantly different each month, but why does smog reach unhealthy levels only during certain times of the year?” said Sate Sampattakul, a lecturer in Chiang Mai University’s Industrial Engineering faculty. “While we’re pointing the finger of blame at traffic, we are forgetting to talk about other problems like field burning or industrial factories.”

In fact the findings indicate the pollution is caused by a matrix of factors rather than one smoking gun. 

There’s also wind speed, air ventilation, temperature, air pressure, rainfall, and cloud cover, to name a few. The study found that days with higher wind speeds and better air ventilation sometimes corresponded to less pollution – and sometimes not.

That gets at another key problem identified in the report, a lack of helpful data.

While vehicles are to blame for the pollution, there were no records of how many were on the road each day, nor estimates of how much carbon monoxide was emitted. 

Despite factories nationwide being told to install standardized emissions monitoring systems, only four out of 260 Bangkok factories had done so. The government will require the installation of such Continuous Emissions Monitoring Systems at more than 600 factories nationwide starting June 10.  

Burning issue

Data from Thailand’s space agency found a link between high levels of hazardous PM2.5 microparticulate pollution and agricultural burning in Bangkok’s surrounding provinces. 

In fact, it seemed the worst on the days with excessive agricultural burning that was over a hundred kilometers away. 

While April 8-10 recorded Bangkok’s highest PM2.5 levels, there was only two such fire hot spots within its borders. But in nearby Suphan Buri province, a large wave of fires were set, with 66 hot spots detected. Many more fires, at least 126, also raged in the surrounding provinces of Ayutthaya, Pathum Thani, Nakhon Nayok, and Nakhon Pathom. 

Farmers are often singled out in the the blame-passing game played by the political class. Agricultural burning may have massive impacts on everyone, but it makes simple economic sense to a farmer looking to clear last harvest’s waste in a cost-effective way. 

It mostly involves rice, sugarcane, and corn and happens between December and April.

Blight without borders

Rocket Media noted that smog and air pollution are not only domestic issues but transnational problems. Crops burned in neighboring countries, especially Myanmar and Laos, also contributed to the pollution. In April 2022, more than 63,000 fire hot spots were recorded in Myanmar and 64,569 in Laos – the highest recorded all year.

Greenpeace Thailand reported that Myanmar’s economy rests heavily on the production  of corn and animal feed, while Laos depends mostly on rice. 

“Can smog travel from Myanmar or Laos to Thailand’s northern region or even Bangkok? Definitely, it can, depending on the wind flow pattern and spatial distribution of air pollution,” Sate said. “Sometimes, smog can even travel thousands of kilometers.”

Bangkok around this time in a previous year. Original photo: Maimiiname / Twitter

Hazy problems, hazy solutions

Given the complex and interdependent factors, there’s no one-size-fits-all solution to tackling the smog, Sate said.

He said that because studying smog is “not that straight-forward,” looking at fire hot spots and he air quality index may not be enough to understand and solve the pollution problem. Wildlife burn scars and area-by-area studies also need to be taken into account.

“Combustions are complex and vary in each area. Therefore, it is better to classify what each area is like,” he said. “We need to see how much combustion occurs in each province and which kind of area it is. What kind of forest or which crops are the main things produced in that area, for example.”

Thailand still does not have explicit laws aimed at tackling the pollution. 

Since unusually thick smog first clouded Bangkok in 2018, city residents have been forced to take their own measures by closing their doors and windows, buying expensive air purifiers, or wearing N95 face masks long before the pandemic. 

Bangkok around this time in a previous year. Original photo: Maimiiname / Twitter

The government initially responded with empty stunts such as spraying water from a few drones at press events. More recently, officials have taken reactionary steps such as banning outdoor activities at schools and encouraging people to work from home

Since smog occurs seasonally from roughly December through April, the problem has been handled like a “temporary catastrophe,” according to one environmentalist. 

“If you take the PM2.5 issue as if it’s a catastrophe, then you’ll only care about it temporarily. In fact, this issue is actually like a sleeping giant,” said Bunnaroth Buaklee of the Chiang Mai Breathe Council.

“It’s related directly with the infrastructure of the manufacturing sector and social behaviors, which would not be developed sustainably. We need changes all year round. This is the kind of problem where you can’t just achieve short-term solutions in a few months,” he added.

Legislative inaction

In 2018, the cabinet elevated the PM2.5 issue to its national policy agenda as a problem that must be solved immediately.

But that didn’t happen, obviously. Coconuts own daily pollution data sampling found that the average annual pollution had overall fallen modestly for two consecutive years before bubbling back in 2023. So far this year, it’s about 16% worse than during the same period in 2022.

A clean air bill proposed by the ruling coalition’s Bhumjaithai Party in 2021 was sidelined by Prime Minister Gen. Prayuth Chan-ocha before it could even be debated.

A civil society group called Thailand Clean Air Network, or Thailand CAN, has drafted a separate bill (available in English). Proposed to the parliament in January 2022, it has never been taken up for deliberation. 

Rocket Media Lab’s full report is available on its site.

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