Two people stand along the Bund yesterday, when the city’s air quality improved.
Shanghai’s environmental authority yesterday said its inaccurate air quality forecast for last weekend was due to the complicated conditions it needs to take into consideration.
The Shanghai Environmental Monitoring Center had forecast the weekend’s air quality to be good, but it proved to be the city’s longest period of air pollution in the past six months with PM2.5 readings exceeding 300 micrograms per cubic meter at its peak, four times the standard.
The center said autumn and winter are the worst seasons for air pollution. The city usually has 15 days of air pollution per year.
It added that it was difficult to forecast air quality and it was accurate more than 80 percent of the time.
“We have to consider the weather conditions, the changes in pollution sources as well as the changes in the pollutants and there are many uncertainties and possibilities,” said Fu Qingyan, a chief engineer of the center.
The city’s air improved yesterday as the wind changed direction.
The PM2.5 readings, a gauge of airborne pollutants measuring less than 2.5 microns in diameter, started to drop from a peak of 180 micrograms per cubic meter at 6am yesterday to below 40 micrograms after midday.
The average PM2.5 density in downtown districts was only 17.1 micrograms per cubic meter at 5pm. However the average level for the past 24 hours was still as high as 121.1 micrograms per cubic meter due to high densities before 6am.
The nation’s maximum 24-hour PM2.5 reading for good air quality is 75 micrograms per cubic meter.
Li Juan, a forecaster at the center, said the drop of PM2.5 was because the wind got stronger and changed direction yesterday morning, ideal for dispersing pollutants.
The air quality today is expected to be good.
Last night’s rain should end by noon today, the bureau said. The mercury will range between 15 and 18 degrees Celsius.