Maybe you do not aware that the polluted air in big city with flowing dust had already causes damage to your lungs. To attract people's aqttention, they print the picture of lungs on the hoover bags to simulate the damge wich polluted air bring to people's lungs. This is a warning to wake people's environmental protection sense. They will give away those hoover bags to the public on the street. People who get that bag would feel interesting first, and then will understand that: Bags are disposable, but your lungs are not! So everyone should pay attention to the quality of air and protect the environment.
Agency: Guangdong, Beijing, China.