Exhaust fumes from vehicles, industry, and construction impact air quality the worst.

According to the latest study, air quality in six out of the city's 12 industrial and processing zones — Cat Lai, Linh Trung 1 and 2, Tan Binh, Tan Tao, and North-western Cu Chi — has worsened since last year.

Exhaust fumes have become a very worrisome issue, with the pollution they cause exceeding permissible levels in most categories.

The rapid growth in the number of vehicles has also sharply worsened noise pollution.

"HCM City is one of the noisiest cities in the world," Assoc Prof Nguyen Dinh Tuan, former principal of HCM City's Natural Resources and Environment University, was quoted as saying in Sai Gon Giai Phong (Liberated Sai Gon) newspaper.

On all major roads, noise levels were found to exceed permissible levels.

According to Prof Nguyen Van Phuoc, head of the Natural Resource and Environment Institute, since 2005 Viet Nam has been applying Euro 2 standards for vehicles, but enforcing them has been very hard because of the shortage of testing equipment.

Inspectors from the city Department of Natural Resources and Environment also admitted that controlling emissions from factories is also becoming more and more difficult since many of them occur at night.

Most of the city's automatic air pollution measurement stations are not functioning any longer but have not been repaired.

Pollution measurements are therefore crude and lack credibility, making it hard for authorities to find solutions.

"To mitigate the air pollution, the most important thing is to set up a 24-hour automatic air measurement system around the city," Tuan said.

"From that system, a trustworthy database for air pollution can be set up, and causes as well as solutions sought."

The city has approved the setting up of a new system.

Phuoc said: "The local community should be mobilised to improve air quality because residents suffer directly. The community must be involved in the environment management system."

He wanted the public to take part in managing the environment.

Information and figures related to air pollution should be publicly announced to enable the community to become aware of air pollution and the need to protect the environment, he added.