Bangkok. There are two pictures Thai air pollution expert Supat Wangwongwatana likes to show whenever he talks about Bangkok's transition, in a little over a decade, from a city blanketed in smog to one boasting clear blue skies.
The first, taken in the mid-1990s, shows the skyline of downtown Bangkok. Most buildings are in silhouette, shrouded in a thick layer of haze. The Baiyoke Tower, back then the city's tallest building, was still under construction.
The second, taken a decade later from a similar angle, looks dramatically different. The sky is blue, the clouds are visible, and the buildings bathed in sunlight.
"Sulfur in diesel fuel and gasoline back in the early 1990s was 10,000 parts per million. Today, it is less than 50 ppm," said Supat, referring to a natural component of crude oil that contributes to air pollution.
"That early technology enabled us to reduce emissions," he said, citing processes for producing cleaner fuel and catalytic converters that make exhaust pipe fumes less toxic.
The World Health Organization (WHO) calls air pollution "a public health emergency." An estimated 6.5 million deaths, nearly 12 percent of all global deaths, were associated with indoor and outdoor air pollution in 2012, the bulk in the Western Pacific and Southeast Asian regions, WHO data shows.
"If nothing was done at all during the last 20, 25 years, I cannot imagine what Bangkok would be like now. People would probably be sick from air pollution," Supat shuddered.
The former director general of the Pollution Control Department (PCD) at Thailand's Ministry of Natural Resources and Environment was one of a number of technocrats who led efforts to rein in Bangkok's rising air pollution levels in the 1990s.
They eliminated lead in fuel, imposed emissions controls based on European norms, and regulated construction sites, despite stiff resistance from powerful oil refineries and the automobile industry.
Taxis now run on cleaner liquefied petroleum gas or compressed natural gas, and motorcycles no longer spew black smoke from their tailpipes.
Experts say these efforts have helped Bangkok avoid the situation of other megacities such as Beijing and Delhi, where air pollution has reached such hazardous levels that even healthy people can fall ill simply from being outside.
They warn, however, that Bangkok risks dangerous air pollution levels again due to residents' insatiable appetite for vehicles. Nearly 49,000 people died from air pollution in Thailand in 2013, a joint World Bank and University of Washington report said.
While most locations in central Bangkok are well within safe levels as defined by Thailand's Air Quality Index (AQI), it does not factor in PM2.5, fine particles that pose the greatest risks to human health. Bangkok's annual average of those particles is 2.4 times the WHO's safety threshold, the UN agency says.
"PM2.5 can go into blood vessels and cause chronic health problems," said Tara Buakamsri, Thailand country director for Greenpeace Southeast Asia.
If you do not include those particles in the Air Quality Index, "you cannot see a comprehensive picture," she added.
Tighter Emissions Limits
Bangkok, home to some nine million people, remains relatively smog-free, even though vehicle numbers have been increasing every year, experts say. In the first four months of 2017, the city registered 300,000 new vehicles, including buses and motorcycles, bringing the total to nearly 9.5 million.
Despite having the second-worst traffic congestion in the world after Mexico City, according to a global traffic index compiled by navigation company TomTom, Bangkok topped a 2015 list ranking popular tourist destinations on their air quality, from UK-based firm Airport Parking and Hotels.
It may not stay there for long.
"Since the 1990s, the number of automobiles is increasing, so you have more congestion and more sources of emission. That's a big challenge," said Bhichit Rattakul, who founded the Anti-Air Pollution and Environmental Protection Foundation a decade before being elected governor of Bangkok in 1996.
To combat this, the PCD has reached preliminary agreements to impose the Euro 5 standard, which further limits pollutants in fuel, by 2023 for oil refineries and by 2024 for vehicles.
"The important thing is that the Thai government implements these policies with Thai industry," said Teera Prasongchan, chair of the Thai Automotive Industry Association's committee on technical issues and deputy general manager of Toyota Motor Thailand.
"That means we have to sit down and talk, and compromise with each other," he added.
Thailand has been using the Euro 4 standard since 2012, while the latest standard is Euro 6.
The upgrade in six to seven years may seem a long way off, but Supat, who has retired after working on air pollution issues for almost three decades but still advises the PCD, said it pays to be patient. The important thing is to "have a fixed and endorsed timeline," he said.
Bangkok is an example of what other Southeast Asian cities can do to improve air quality, said Glynda Bathan-Baterina, deputy executive director of the Manila-based NGO Clean Air Asia. Still, these "tailpipe solutions" only tackle emissions on a per unit, per vehicle basis, she noted.
"The real solution is looking at a mass transport system that can bring massive numbers of people in and out of the city while encouraging them to leave their vehicles at home," she said.
Bangkok is planning 12 more rapid transit train lines but they will not be ready until 2029.
Other low-emission solutions, such as electric or hybrid cars, are still a rarity in Thailand. Teera from Toyota said car manufacturers here are adopting a wait-and-see approach due to concerns over infrastructure and energy supply.
In the meantime, politicians and city leaders need to enforce higher air quality standards to keep residents safe and healthy, former governor Bhichit said.
"The public can avoid the bad places but ultimately, that's not the direction the city should be moving in," he said.
During Bhichit's time in office, air pollution was so bad he put up signs urging people to avoid Silom Road in downtown Bangkok in the afternoon, and cracked down on vehicles whose emissions exceeded standards.
"People were not happy with me. They drove to my house and blew their horns every morning. The automobile industry also made a big noise," he recalled.
"But I did not listen much."