I'm planning to travel in Beijing in 1st week of April. But i'm afraid about the latest news about the smog pollution.

According to the latest weather forecast, the smog pollution is serious and as I know, the AQI for today is around 464. But the news said that the rain in the following days will improve the air condition.
Besides air problem, it is safe to travel in that place.
For clothes, you are suggested to take your Spring clothes such as the T-shirts and jeans. In addition, I suggest you to prepare a mask in case of the smog days.