A 3x3 grid juxtaposing a photo with the past eight days of the same building is the regular post by Zou Yi. [Photo by Zou Hong/China Daily]

His Jan 14 tweet, for instance, reads: "#No 1 Bus# Driver says: 'Haze is suffocating Beijing for the third day and is getting even worse ... It's reported Beijing will invest $130 billion more to curb air pollution over three years. I just hope the government won't waste taxpayers' money'."

On Jan 4, Zou printed two huge grids of all his BTV building photos from 2013 and 2014.

The municipal watchdog released a government report on the capital's 2014 air conditions the same day.

"It's a fortunate coincidence," Zou says.

"All stakeholders in environmental issues should be fully involved in decision-making. Grassroots supervision motivates and pressures governments to solve problems with greater transparency."

Zou's friend Yan Huang, who works for two environmental nonprofits in Beijing and Guangdong's provincial capital Guangzhou, says: "Zou Yi is a man of action, who discloses the reality of Beijing's air pollution with his photos. I agree with his approach (to engage social issues). Rather than debating, he takes action. He lets facts speak for themselves in a mild and practical way. His photos reveal truths about false official figures. He's an unsung hero in the campaign to publicize air-quality data."