A chemistry teacher in Hanoi has made an official apology to online air quality index monitor AirVisual after triggering a smear campaign in Vietnam that caused the company’s mobile app to be pulled from digital distribution platforms in the country.

AirVisual said on Monday it was under coordinated attack to “discredit” the company after its data showed Vietnamese cities among the world’s places worst hit by air pollution.

“The AirVisual apps and Facebook page are currently no longer accessible in Vietnam,” the company said, adding that it was due to “abusive and threatening messages” posted on Facebook and on the Apple App Store and Google Play Store.

The attack came after Vietnamese Facebook user Vu Khac Ngoc, an online chemistry teacher with almost 350,000 followers, said in a lengthy post that AirVisual was manipulating its data in order to sell air purifiers made by its parent company, IQAir, Reuters said.

Ngoc did not offer any evidence to back up his claims, but the post - which claimed the AirVisual ranking would harm tourism in Vietnam and urged people to leave negative reviews of the app - quickly received thousands of shares and likes.

The post appears to have been removed or hidden as of Tuesday morning.

In an “apology to AirVisual developers” posted on his Facebook account on Tuesday afternoon, Ngoc said he had been “mistaken” about AirVisual’s air quality index (AQI) live rankings.

He admitted his earlier analysis of the way AirVisual compiles its rankings has given rise to “negative reviews” of the app on digital distribution platforms.

Ngoc said he now understands that the rankings do not imply Hanoi is the world’s most polluted city, after reading an explanation published on the AirVisual website on Sunday.

“I regret that my negative comments about AirVisual has affected and obstructed the app’s operations in Vietnam,” Ngoc wrote.

“I hope that [since] misunderstandings about AirVisual’s rankings have been cleared up, you will soon resume operations in Vietnam and continue to provide more useful and authentic information on, and contribute to, providing solutions for improving air quality in [Vietnam’s] major cities,” the apology reads.

Ngoc’s apology has garnered some 5,000 “reactions” on Facebook and been shared nearly a thousand times on the social network after three hours.

In a Facebook post on Saturday, Ngoc pointed out reasons why he thought AirVisual’s AQI ranking was unreliable, bashing the company’s method of collecting, compiling and presenting data that intentionally instills fear among the public about the pollution situation in major cities.

Hanoi was at times in September the city with the highest AQI in the world, surpassing the likes of Beijing and Bangkok, according to AirVisual’s “major city ranking,” a live pollution ranking of around 90 major global cities.

According to Ngoc, this ranking was false and misleading, motivated by AirVisual’s aim of promoting sales of its parent company’s air purifiers and face masks.

“What we need to do is prove to [AirVisual] that while Vietnamese people might be naive, we are not meek,” Ngoc wrote.

He called on his followers to take part in a “three-point plan” to discredit AirVisual, which involved reporting and giving one-star reviews on the company’s Facebook page, uninstalling and reporting their mobile apps, and pressuring the company into issuing an official apology.

Ngoc also called for mass reports of the news sites which had published articles on Hanoi’s pollution based on AirVisual’s data.

AirVisual has clarified that its “major city ranking” results “does not mean that Hanoi is the world’s no. 1 polluted city.”

“At any one time, a city can top the live ranking, as happened with London and even San Francisco last year,” AirVisual said in a statement published on its website on Sunday.

The air quality tracking site said it also publishes a separate annual world ranking in partnership with Greenpeace, and that a report published in March showed that “Hanoi was not in the world’s top 200 most polluted cities in 2018.”

AirVisual is working with Apple, Google and Facebook to confirm that it has been unfairly attacked, and to make the AirVisual apps available again in Vietnam, the app operator said.

It had been among the most downloaded apps in Vietnam, and was at one point last week the most-downloaded app on App Store before it was removed, Reuters reported.

Like us on Facebook or follow us on Twitter to get the latest news about Vietnam!