In this edition of the link, we take a look at challenges of tackling pollution around the globe. In China's Hangzhou city, the main session of this year's World Environment Day is being held, with a focus on air pollution. The four-day event gathered over one thousand officials, scholars and environmentalists from around the world. They called for more attempts to raise awareness about air pollution and tackle it. CGTN's Zheng Yibing has more.

An inconvenient truth. According to the United Nations, over 90 percent of the human population breathes polluted air. Some seven million deaths every year are blamed on bad air quality. That's why the UN urges all sides to act decisively at this year's World Environment Day.

JOYCE MSUYA ACTING EXECUTIVE DIRECTOR, UN ENVIRONMENT "From pressuring politicians and businesses to changing our own habits, we can reduce pollution and beat climate change."

Air pollution has never attracted so much attention, particularly in China, where in more than 60 percent of the nation's cities, the concentration of particulate matter 2.5 per cubic meter is still above 35, far beyond the strictest standard of ten set by the World Health Organization. But changes are happening.

HAN ZHENG VICE PREMIER OF CHINESE STATE COUNCIL "In recent years, China has made unprecedented efforts to beat air pollution. Strong results have been achieved."

Last year, the average density of PM2.5 per cubic meter fell by 42 percent in the first 74 pilot cities. It's visible in key cities like Beijing. Behind this are tougher law enforcement, enhanced science and technological support and upgraded industrial standards.

AJAY MATHUR DIRECTOR GENERAL, THE ENERGY & RESOURCES INSTITUTE "As you know, air pollution is very huge in India as well. We have been looking for the success that China has had, particularly in the capital and Hebei region and see how we can use those to reform policy in India."

And besides praise, many urge further efforts and cooperation.

JORGE THOMSEN PROGRAM DIRECTOR OF CLIMATE SOLUTIONS, MACARTHUR FOUNDATION "It really requires national plans and a national approach, which the government is working on, but clearly there is still a lot of work to be done."

BAN KI-MOON FORMER UN SECRETARY-GENERAL "If we work together, we can make the world more harmonious and potentially very sustainable."

Although there are still uncertainties and yet people are optimistic at least at the celebration and inspiration for the next step.

ZHENG YIBING HANGZHOU, ZHEJIANG PROVINCE "The path to clean air and a clean world is not easy, but as participants here said, things can change if everyone does their part and will continue the efforts in the days and years to come. Zheng Yibing, CGTN, Hangzhou, Zhejiang Province."