Shanghai's air quality briefly hit highly polluted levels yesterday due to haze in the middle and downstream sections of the Yangtze River.

For the first time, the Shanghai Environmental Monitoring Center issued an air-quality warning that included the new PM2.5 measurement. From Saturday night the PM2.5 figure had grown to three times the nation's new standard by 10am yesterday.

According to the two monitoring sites that began to release the data last Thursday, PM2.5 particles measured over 230 micrograms per cubic meter at 10am in Putuo District and almost 220 at 10am at Zhangjiang in the Pudong New Area.

The maximum PM2.5 allowed under China's new standard is 75 micrograms per cubic meter.

However, the PM2.5 measurement dropped quickly at both sites after 10am and returned to below the standard about 2pm.

The center's warning about poor air quality was issued at 10:42am yesterday after air pollutants had begun to increase at noon on Saturday due to the haze.

The PM10 particle concentration was 278 micrograms per cubic meter (compared to the limit of 150) and PM 2.5 was 206 at 9am.

The center said people with heart problems or respiratory diseases and those with weak immunity should stay inside. PM2.5 can affect air quality and visibility and pose major health risks as the tiny particles are small enough to lodge deep in the lungs and even enter the bloodstream.

Shanghai's air quality today is expected to be "good," the second-best in a five-tier category.

The city will enjoy another two days of dry weather until rain returns on Wednesday. The sky is forecast to be a mix of clouds and sun today and tomorrow. The maximum temperature will range from 9 to 12 degrees Celsius, after lows of 2 to 3 degrees.