Heard news Beijing now hit sandstorm (bad quality air polution). Is it safety to travel to beijing this week (8/3-12/3)?

Yes, it is safe enough to travel there. According to the weather forecast and latest news, it will be mostly fine during that time. Anyway, in case of invisible air pollution, a mask shall be taken along. And there will be big temperature gap between daytime and nights, you'd better wear relatively warm clothes.