背景知识：

The market for dust masks and air purifiers is booming in Beijing because the capital has been shrouded for several days in thick fog and haze.

近几日北京持续被浓重雾霾笼罩，市场上防尘口罩和空气净化器的销量剧增。

雾（fog）和霾（haze）是这两天我们经常听到的两个词，二者的区别为：雾的相对湿度（the relative humidity）一般在90%以上，而霾在80%以下，但通常两者并存。能见度（visibility）在1公里以下的称为雾，1公里以上但小于10公里的属于灰霾（dust haze）现象。

近两日，部分地区的空气质量指数（air quality index, AQI）可能达到极重污染，北京多地PM2.5浓度“爆表”。PM2.5就是指“可入肺颗粒物”，PM的英文全称为particulate matter（微粒物、悬浮微粒），PM2.5就是指大气中直径小于或等于2.5微米的颗粒物，可直接进入人体的alveoli of the lungs（肺泡），它的直径还不到人头发丝粗细的1/20。PM2.5主要来自burning of fossil fuels in vehicles（机动车燃油）, power plants（发电厂） 以及 various industrial processes（各类工业生产）。

相关报道：

1、                   Pollution may make economy stumble

    污染可能绊住经济发展的步伐

Construction, tourism 'will be hit by haze and measures to tackle it'

As a number of cities try to clear the air, specialists in Beijing warn that the pollution and emergency responses to reduce it could damage the economy and tourism.

Authorities in the capital said on Monday they had ordered 58 factories with high emissions to suspend operations. Work at construction sites that could cause dust, such as leveling land, were also halted.

The move followed similar action in Shijiazhuang, in neighboring Hebei province, where authorities stopped work at more than 700 construction sites.

Both cities have advised young children and the elderly to stay indoors.

The capital has ordered kindergartens, primary and middle schools to scrap

physical education classes until air quality improves.

"Pollution from the 58 factories has been cut, and we believe we can reduce their emissions by 30 percent," Li Hong, deputy director of Beijing's Economy and Information Technology Commission, said at a news conference held jointly by several departments on Monday.

The factories ordered to halt operations include two cement plants, and others involved in chemicals, metallurgy and building materials, he said.

Up to 30 percent of government vehicles have also been banned from the capital's roads on heavily polluted days, according to a spokesman for the Beijing Traffic Management Bureau.

Drivers found guilty of breaking the rules face penalties, but the spokesman did not elaborate.

Air quality dropped dramatically on Thursday and steadily worsened over the weekend, said Zhang Dawei, who heads the city's environmental protection monitoring center.

By Saturday, official data showed the density of PM2.5 — particles of 2.5 microns or smaller that can damage the lungs — had reached 900 micrograms per cubic meter in several Beijing districts.

It was the highest level recorded since authorities began releasing the data to the public in early 2012.

The safe daily level is 25 micrograms per cubic meter, according to the World Health Organization.

Coal emissions and vehicle exhaust fumes played a major role in the pollution and a low-pressure weather front trapped the polluted air.

"Beijing is a huge city with a lot of heavy industry," Zhang said. "Under certain atmospheric conditions, the pollution is trapped.''

The China Climate Bulletin, released by the China Meteorological Administration on Monday, said hazy conditions primarily occurred in two periods; between January and March and October and December.  （From Chinadaily）

2.          Beijing's hazardous pollution sparks Chinese media anger

Chinese media have reacted strongly to dangerous levels of pollution recorded in many northern cities in recent days.

In the capital, Beijing, at the weekend, air pollution soared past levels considered hazardous by the World Health Organization.

The official People's Daily said the smog was a "suffocating siege" which had to be urgently addressed.

The state-run China Daily said the country had to learn to balance development with quality of life.

Meanwhile, the tabloid Global Times said China was risking serious long-term environmental damage. Smog also dominated social media sites.

Over the week, a dense smog had been gathering over Beijing and some 30 other cities in northern and eastern China, with visibility down to 100m in some places.

Official Beijing city readings on Saturday suggested pollution levels of over 400. An unofficial reading from a monitor at the US embassy recorded levels of over 800.

WHO guidelines say average concentrations of the tiniest pollution particles - called PM2.5 - should be no more than 25 microgrammes per cubic metre. Air is unhealthy above 100 microgrammes and at 300, all children and elderly people should remain indoors.

Once inhaled, the tiny particles can make people more vulnerable to respiratory infections, as well as leading to increased mortality from lung cancer and heart disease.

The Xinhua state news agency said there had been a sharp rise in people seeking treatment at the hospitals in the capital for respiratory problems.

The mother of one eight-month-old baby told the BBC her child had suffered from lung problems for months and that they recently worsened after an outing. Ms Li said she had resorted to keeping a basin of water in the house in the hope it might act as an air purifier.

"It would be helpful if the city has less cars and the city could [place] curbs on car emissions," Ms Li said.

'Poor planning'

On Monday, Beijing authorities said levels had dropped to around 350, but school children were being kept indoors and media reports were warning the public to do the same and to avoid strenuous activity.

The build up of pollution has been put down to a lack of wind and a cold spell, rather than a surge in production of pollutants. But an editorial in the China Daily said there was no reason "for us to not reflect on what we've contributed to the smoggy days".

It blamed the pollution on poor urban planning and a rapid increase in car ownership, saying residents had to cut down their use of private cars.

"In the middle of a rapid urbanisation process, it is urgent for China to think about how such a process can press forward without compromising the quality of urban life with an increasingly worse living environment," said the editorial.

"The air quality in big cities could have been better had more attention been paid to the density of the high rises, had more trees been planted in proportion to the number of residential areas, and had the number of cars been strictly controlled. These are the lessons China should learn for its further urbanization."

The People's Daily, the official mouthpiece of the ruling Communist Party, ran a front page editorial demanding: "Let us clearly view managing environmental pollution with a sense of urgency."

The tabloid Global Times said measures taken so far to address pollution in China, which it called the "biggest construction site in the world", had failed to alleviate the problem.

It accused the government of dealing with environmental problems in too low-key a way, and called on it to "publish truthful environmental data to the public" to allowed them to help solve the problem.

"The public should understand the importance of development as well as the critical need to safeguard the bottom line of the environmental pollution," it said.

Social media was also dominated by comments on the pollution, with users of the Twitter-like Weibo site saying the government should do more to prevent pollution affecting their lives. （From BBC）