Official cars ordered off roads during hazardous pollution

 　　BEIJING, Jan. 29 (Xinhua) -- Thirty percent of official cars in Beijing should not be used when there is "extremely bad" pollution, traffic authorities confirmed Tuesday.

　　The order was implemented¹ on Monday evening to help combat the fourth round of heavy smog to hit the capital city in four weeks, Beijing Traffic Management Bureau said.

　　Traffic authorities will monitor, take pictures and trace official cars that violate the government order. Whatever department the vehicles belong to will be punished.

　　Beijing has a list of official cars that should not be used when there is heavy pollution.

　　The capital categorizes air pollution days as "bad," "seriously bad" and "extremely bad" depending on indexes that include measurements of both fine and coarse air particles and ozone² levels.

　　Beijing's air quality has worsened again since Monday, with a significant thickening of the PM 2.5, or airborne particles measuring less than 2.5 micrometers in diameter.

　　At 10 a.m. Tuesday, the average concentration of PM 2.5 was tested at 354 micrograms per cubic meter.

　　To curb³ pollution, the government has introduced a number of measures, including moving heavy polluters away from urban districts.

1 implemented   

v.实现( implement的过去式和过去分词 )；执行；贯彻；使生效

参考例句：

• This agreement, if not implemented, is a mere scrap of paper. 这个协定如不执行只不过是一纸空文。 来自《现代汉英综合大词典》
• The economy is in danger of collapse unless far-reaching reforms are implemented. 如果不实施影响深远的改革，经济就面临崩溃的危险。 来自辞典例句

2 ozone   

n.臭氧，新鲜空气

参考例句：

• The ozone layer is a protective layer around the planet Earth.臭氧层是地球的保护层。
• The capacity of ozone can adjust according of requirement.臭氧的产量可根据需要或调节。

3 curb   

n.场外证券市场，场外交易；vt.制止，抑制

参考例句：

• I could not curb my anger.我按捺不住我的愤怒。
• You must curb your daughter when you are in church.你在教堂时必须管住你的女儿。