The creen shot of the app.

World Wide Fund for Nature (WWF) China and OgilvyOne Beijing recently launched an iPhone app Blue Sky to support the annual Earth Hour event. With a simple finger swipe, users can turn their pictures of polluted gray skies into clear blue skies.

They can not only share the before and after photos on WeChat and Sina Weibo, but can also sign their phone screens and send their signatures to the WWF website. Blue signature of all supporters will be combined on the website to clear away a gray sky.

Established in 2009, Earth Hour is a global event that encourages participates to commit themselves to protecting the environment by turning off unessential electrical devices for an hour. It has become one of the biggest public engagement events in China, taking place in some historic places such as the Great Wall.

Li Bingbing, Chinese movie star and WWF Earth Hour global ambassador, will launch the event on March 29 at 8:00 pm at Beijing Shimao Tianjie, a popular shopping destination.

Her signature on the app will be projected onto a large overhead screen. Passersby can also join the movement by signing their names through the Blue Sky app on their iPads onsite. These blue signatures will transform the gray skies into clear ones.

Dan Wang, brand manager of WWF China, said an innovative mobile app can help them get more Earth Hour supporters in China, because the smartphone market in the country will reach 90 percent penetration rate this year.

He said the government can improve the air quality, but the WWF wants to encourage people to think and support their initiatives, and this app is a step in that direction.