A group of artists who staged a silent demonstration against China’s poor air quality were stopped by authorities in the city of Chengdu and detained for several hours before being released, BBC News reports.

The artists, who are concerned about the heavy smog affecting the Sichuan province and who believe a petrochemical plant in nearby Pengzhou might be adding to the pollution, organized the protest on December 11 using the messaging app WeChat.

One artist, who did not give his name, said, “Chengdu’s air pollution is really severe, I’ve been feeling unwell. I cough all the time. [I thought] we want to take some action, we should stand up.”

They walked around the city wearing facemasks and were stopped by police. Members of the group began arguing with officers who asked them to leave. Eight artists and at least one passerby were arrested. They were questioned for five hours and then released the following morning.

Concerns over pollution have led to a surge in small-scale protests in China. Throughout the month of December, a number of actions have been planned to bring attention to air quality. In Xi’an, a group of art students placed facemasks on eight hundred lion statues located on their college campus. In Chengdu, authorities have shut down Tianfu Square in anticipation of demonstrations initiated via social media. In response, Chengdu officials said they will take serious steps to combat the pollution in the area.