Shanghai's air quality was lightly polluted yesterday due to cold air from the north and regional mist, said the Shanghai Environmental Monitoring Center, which warned the elderly, children and those with respiratory diseases to avoid going out or taking protective measures if staying outdoors in the morning.

Today the city is expected to have good air quality, second-best in a five-tier category.

According to the center's real-time monitoring data, PM10 particulates started to rise at 1am yesterday and peaked at 10am. Then the density dropped quickly in the afternoon, with visibility in most areas of the city improving to 5 to 10 kilometers, reported the Shanghai Meteorological Bureau.

Starting tomorrow, with the strengthening of a warm and wet air current from the southwest, drizzle is expected to return to the city for at least three days. But temperatures will not change much. The daily high is forecast at 7 to 8 degrees Celsius, after lows around 2 to 4 degrees, said the bureau.

Air quality has been a major concern for local government and city residents, and Shanghai Mayor Han Zheng vowed anew yesterday to take stricter anti-pollution measures.

Reducing smog a challenge

The city will close 600 heavily polluting or energy-consuming manufacturing operations, it has said previously.

Shanghai will also take stricter measures to protect water resources and monitor air quality, including PM2.5, or particles less than 2.5 micrometers in diameter, the major pollutant affecting air quality and visibility.

PM2.5 is not included in the normal air quality-monitoring system yet.

The real difficulty lies not in monitoring but in actually controlling pollution.

Shanghai often receives dusty pollutants from the north, and a better-coordinated joint effort within the Yangtze River Delta region, such as was used during the 2010 World Expo, is needed.

Han also talked about many more cutting-edge and efficient anti-pollution measures, but how to pay for such efforts remains a problem.

It was easy for Shanghai to be among the first Chinese cities to monitor and release PM2.5 data, but reducing the pollution is another matter, noted Fan Xianbiao, vice director of the Shanghai Environmental Protection Bureau.

Fan said the city's air can be improved only if all the city's government departments, companies and citizens work together along with other Yangtze River Delta cities, as during the World Expo in 2010.

The city's air was rated as good or excellent over 95 percent of the time during the 184-day expo, and residents could often see blue sky and white clouds.

Fan said such success came because the city's traffic and agricultural authorities as well as district governments worked together to control vehicle emissions and reduce pollution, but the cooperation stopped after the world's fair ended.

He asked the city government to launch a new campaign among local government departments to improve air quality.

The city will focus on renovating technology at power plants and eliminating high-polluting vehicles, Han said yesterday.