City once notorious globally for its thick blanket of smog now outperforms San Francisco, Melbourne, Paris and Berlin.

Bangkok, Thailand – It’s the sort of statistic that will make most long-term residents of this city sit up and do a double take.

In a comparison of air quality in popular tourist destinations, the Big Mango – as the Thai capital is often called – was found to have the best air quality of them all.

The city can be expected to comfortably outrank fume factories such as Beijing and Delhi.

But what’s surprising about this ranking is that Bangkok – once notorious globally for its thick blanket of smog – now outperforms San Francisco, Melbourne, Paris and Berlin.

The change didn’t take place overnight. Instead, it was the result of a concerted, coordinated effort by the city authorities and international organisations such as the World Bank.

The strongest proponents of these plans were a group of Thai technocrats who had gone to the US for higher studies and came back armed with the regulatory knowledge that underpins the standards of the Environmental Protection Agency (EPA).

Bangkok’s turnaround demonstrates at once the far-reaching positive influence of the EPA and the potential global repercussions of any lowering of its standards on Donald Trump’s watch.

On the campaign trail, the Republican president-elect repeatedly boasted that he would repeal as much environmental regulation as he could get his hands on. And this week, Trump picked a known sceptic of climate science to be the next EPA administrator.

Under siege in Delhi

When I first moved to Bangkok in 2010, I barely noticed the difference between it and the city I had moved from: New Delhi, a city notorious for its dust storms.

This November, the Indian capital found itself under siege, choking on smog that was 16 times the level the Indian government considers acceptable.

Things got so bad that an emergency was declared.

Schools were shut down as residents huddled with their children by their air purifiers to avoid breathing what was the equivalent of two packs of cigarettes a day.

In comparison, I don’t know anyone in Bangkok who would even think of buying an air purifier now.

Bangkok’s buses and cars have switched to natural gas in recent years [EPA]

The rest of the developing world has taken several steps backwards, sacrificing the environment for economic growth.

For instance, four of the 10 cities in the world with the worst air pollution are in India, according to the World Health Organization. Two are in China.

Delhi comes in at number 11. In fact, 12 out of the 25 worst cities are in India, while five are in China. Both countries would do well to look to Thailand as a role model.

One of the biggest causes of air pollutants in Bangkok was diesel buses – many of them were also pumping out dangerous levels of lead into the air.

Driven by a strong awareness campaign about the environmental and health costs of these particles, Thailand managed to go lead-free before the US.

Buses and cars also quickly switched to natural gas, which Thailand possesses in greater quantity than oil.

The other major target was Bangkok’s ubiquitous motorcycle taxis.

Zipping through the lanes of gridlocked cars, motosais – as motorcycle taxis are commonly called – are the city’s get-out-of-jail card for those who actually need to get somewhere on time and can’t afford to spend an hour stuck in traffic.

Authorities pushed motosais to adopt cleaner four-stroke engines.

The efforts aren’t stopping there. The transport ministry is now taking steps to purchase 200 electric buses to replace old ones which are not as environmentally friendly.

Bangkok has really cleaned up its act, even if most people still cling to the old stereotype, with air pollution regularly featuring as one of the top concerns in opinion surveys of residents.

In an age when 8.4 million people die every year from air pollution-related illnesses, and residents of most mega-cities find themselves besieged by smoke, dust, and smog, a tip of the hat to Bangkok.

The heat and humidity here can be stifling, but at least I’m not slowly poisoning myself with each breath.