Blue seas and skies blend together in Zhoushan. [Photo/WeChat account: zjzsrbs]

Zhoushan in East China's Zhejiang province went viral online in recent days for its red night sky on May 7.

It turns out that the red sky was actually caused by the light from local fishing boats scattered throughout the clouds and mist, according to Tang Yue, director of the Zhoushan municipal meteorological observatory.

Zhoushan is known for its blue skies, as the city has been listed among the top 100 cities with the best air quality by Philippines-based Clean Air Asia for many years, with its overall score being around 98 points.

According to the Zhoushan Weather and Climate Bulletin in 2021, the number of cloudy days in Zhoushan was 42, nine days fewer than the year before, while the number of smoggy days was four, eight days fewer than in 2020.

Zhoushan boasts blue skies and billowy white clouds. [Photo/WeChat account: zjzsrbs]

As early as 2008, the Zhoushan meteorological department launched the blue sky index. The index categorizes blue skies into five classes based on air quality, with the first class being the best.

Zhoushan has also taken measures to reduce air pollution in recent years. Statistics show that in 2021, the concentration of PM 2.5 in the city was 15 micrograms per cubic meter, down 11.8 percent year-on-year, and its good air quality rate was 98.1 percent, ranking first in Zhoushan and among the top cities in China.

In the first quarter of the year, the city was ranked third among 168 major Chinese cities in terms of air quality.