A total of 334 days, or 91.5 percent, last year, registered as having excellent or good air quality, 1.9 percent more than in 2008. It was the highest number since records began, the local environmental protection authorities said yesterday.

However, Shanghai faces many challenges such as ozone, haze and acid rain due to high speed of urban construction and economic development in the region, the Shanghai Environmental Monitoring Center said.

There were 107 days with excellent quality, the top grade in a five-tier grading system, last year. The major pollutant in the city was inhalable particle matters, while the incidence of sulfur dioxide and nitrogen dioxide pollutants had dropped after the authorities took action on coal-burning boilers and vehicle emissions.

"Though the figures show we had better air quality, local residents may have had a different impression last year, when there were so many construction sites in the city," said Xi Ailing, a Shanghai Environmental Protection Bureau official. "The dirt and haze were people's major concerns, tarnishing a blue and clean sky."

She said the air quality measurement only calculated big particulate matter, so the system might not include small particulates and dirt. "Smog is not considered for air quality evaluation. However, the government has already realized the problem and kicked off research with meteorological bureau and other neighboring provinces to tackle the issue."

Water quality last year improved a little after the upper reaches of the Huangpu River were renovated. Water at the mouth of the Yangtze River was of good quality, while the Huangpu River was slightly polluted. Suzhou Creek's water had been much improved but, according to the standard, still fell in the heavily polluted category.