The Nanhui area inspectors have won the top prize for environmental cops in Shanghai since 2006. In 2008 the team was honored as an "advanced group in punishing and reforming polluting enterprises."

In that year alone they handled 247 registered cases; polluters paid 6.4 million yuan (US$936,400) in fines, the most of any district in the city. (Nanhui has since been incorporated into Pudong New Area.)

Awareness of the environment has also been raised for both enterprises and residents in the past three years, says Deng Zhihua, captain of the Nanhui Environmental Inspection Detachment.

Many residents call immediately when they smell bad air or see polluted water. Today there's hardly any black smoke to be seen most of the time. Deng recalls that he used to see at least 10 chimneys belching smoke when he drove around in 2006.

Though the suburban environment is generally less polluted than more urban areas, it also has its problems.

Nanhui's 800 square kilometers includes scattered villages and towns, which makes monitoring more difficult.

"Almost all the environment problems in Shanghai can be found in Nanhui alone," says Deng.

They include small local enterprises launched years ago, livestock breeding, small salvage stations and large enterprises either opened in recent years or forced to relocate to the suburbs, he says.

On-site inspections can be difficult. While it's simple to check for noise and polluting solids and refuse, checking on water and air pollution is difficult, says Ye Yuxiang, vice captain of the Nanhui inspectors.

Some plants discharge pollutants secretly at night with concealed pipes, and halt the discharge when inspectors respond to residents' complaints.

They need to spot check and enter the plant at night - not all plant managers open the doors for them - and look for concealed pipes and specialized equipment. Then they need to collect water at the hidden outlet for laboratory tests.

It is also difficult to identify the source of air pollution due to moving air.

Three weeks ago the team received a complaint about a bad smell at a residential area near Kangqiao Industrial Zone. They checked three times but failed to find the source.

"Of course, the residents didn't lie but we cannot do anything unless we smell it," says Ye, who asks people to call immediately when the air is bad.

It took the team almost three weeks to find the culprit among 80 factories in the area. The smell didn't come from discharged air but from fermentation in the pulping process in a paper plant. Hot weather increases the rate of fermentation.

As temperatures rise, so do the number of complaints about bad air, especially when more people open their windows. The team receives 20 to 30 complaints a day.

"It is good that more residents care about the environment, but sometimes we're short of staff to handle so many cases," says Deng, captain of the inspection and monitoring detachment.