Schools in Beijing are to close and outdoor construction to stop after the Chinese capital issued its first "red alert" over smog levels. The red alert is the highest possible, and has not been used in the city before, the state-run Xinhua news agency says.

北京首次将雾霾预警上升至红色之后，学校将停课，室外建筑工地也将停止施工。新华社称，红色预警是最高等级的警报，北京以前也从没启动过。

Authorities expect more than three consecutive¹ days of severe smog. Cars with odd and even number plates will be banned from driving on alternate days.

权威机构预测这次的极端雾霾天气将至少持续三天。北京也将会实行车辆单双号限号。

Current pollution levels in Beijing are actually lower than last week's, but the red alert has been placed because of levels expected over the coming days.

这一周北京的污染程度其实是比上周好一点的，但是红色预警针对的是对接下来几天的雾霾天气。

The order will last from 07:00 local time on Tuesday (23:00 GMT on Monday) until 12:00 on Thursday, when a cold front is expected to arrive and clear the smog.

预警中提到的时间是从当地时间周二早上到周四中午十二点，预计周四将有冷锋过境，带走雾霾。

China's CCTV news channel reported at the weekend that some parts of Beijing had visibility of only 200m (660 feet). Coal-powered industries and heating systems, as well as vehicle emissions² and dust from construction sites, all contribute to the smog which has been exacerbated³ by humidity and a lack of wind.

CCTV新闻频道周末报道了北京某些区域的能见度只有200米（660英尺）。煤动力工厂和供暖系统，还有汽车尾气和施工扬尘，加上空气湿度和最近风力减弱都是导致雾霾加重的因素。

At 18:00 local time (10:00 GMT) on Monday, the air pollution monitor operated by the US Embassy in Beijing reported that the intensity⁴ of the poisonous, tiny particles of PM 2.5 was 10 times above the recommended limit.

当地时间周一晚六点，美国驻北京大使馆的空气污染监测器报告空气PM2.5中有毒微小颗粒的密度已经达到最大允许值的十倍。

The level in Beijing reached more than 256 micrograms per cubic meter in some of the worst-affected areas. The World Health Organization considers 25 micrograms per cubic meter to be a safe level.

北京雾霾的严重程度已经导致一些受影响最严重的区域，空气中每立方米微生物数量超过了256。而世界卫生组织规定的空气中每立方米微生物安全数量是25。

Activists⁵ said the level hit 1,400 micrograms per cubic meter in the north-east city of Shenyang last month, saying it was the worst seen in China.

环保积极分子称，中国东北城市沈阳上月的空气中每立方米微生物数量已经达到1400，这是目前中国出现过空气最糟糕的一次。

Last week, activists from Greenpeace had urged the Chinese government to declare a red alert. Another Chinese city, Nanjing, issued a red alert in December 2013.

上周，“绿色和平”组织已经郑重要求中国政府发布红色预警，中国另一个城市南京就曾在2013年12月发布过红色预警。