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The pollution that hit Hebei province, Beijing and Tianjin in the past week was less severe than last year, monitoring results revealed.

From Feb 20 to 26, Beijing, Tianjin and Hebei were shrouded in smog.

However, environment-monitoring results from the Chinese Academy of Sciences showed that the average concentration of PM2.5 - fine particulate matter with a diameter less than 2.5 microns that can lodge in the lungs - was 11 percent less than it was when smog hit the region in spring 2013, and the peak concentration decreased by 16.4 percent.

"The concentration of pollutants in the smog decreased by 20 to 30 percent in general over the last year," said Wang Yuesi, a researcher from the Institute of Atmospheric Physics under the Chinese Academy of Sciences.

Wang was speaking on Saturday at a forum in Beijing held by the Chinese Academy of Sciences to discuss the cause of the smog.

The institute monitored the concentration of PM2.5 and other pollutants across the country, with 23 monitoring stations in North China. The comparison was based on data collected in January and February this year and January 2013, when severe pollution lasted nearly a month in North China.

Both of these smog events had similar climate conditions, Wang said.

"The monitoring results show that the emergency measures taken to cope with air pollution were effective. But the effect may not be so obvious to the general public because the PM2.5 concentration still caused a deterioration in visibility," he said.

Visibility in the smog was 2 kilometers, while Wang said the visibility will not be improved unless the PM2.5 concentration falls to below 100 micrograms per cubic meter. In February, it was 230 mg per cubic meter.

Beijing's contingency plan includes forcing nearby plants to cut production.

However, Wang said that only long-term solutions will end the pollution.

"The major PM2.5 source comes from coal power stations," he said. "The overall area of Beijing, Tianjin and Hebei accounts for some 0.05 percent of the world, while this region consumes 11 percent of its coal, so you don't have to use your imagination to understand why we are suffering from air pollution. We are living inside a huge chimney."

He Hong, from the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, said: "Our research shows that 'second particles' contribute around 60 percent to the formation of PM2.5 in Beijing and Tianjin."

Second particles are pollutants generated by chemical reactions between different pollutants released into the atmosphere.

"As a result, reducing the emissions of oxynitride and oxysulfide from coal fuel and vehicles is necessary," He said.

However, due to the complex chemical reactions, scientists are not sure about the exact contributing factors of smog. To understand better, the Chinese Academy of Sciences will apply for construction in 2016 of a "smog chamber" to simulate pollution conditions.

Questions:

1. What does smog monitors in North China say about this year’s pollution?

2. Who is in charge of the monitoring?

3. What is the visibility rate in the smog?

Answers:

1. Average concentration of PM2.5 was 11 percent less than it was when smog hit the region in spring 2013.

2. The Chinese Academy of Sciences.

3. 2 kilometers.

（中國日報網英語點津 Helen 編輯）

About the broadcaster:

Nelly Min is an editor at China Daily with more than 10 years of experience as a newspaper editor and photographer. She has worked at major newspapers in the U.S., including the Los Angeles Times and the Detroit Free Press. She is also fluent in Korean.