The weather signs are cloudy and sunny.

(1) According to the weather symbols in Beijing weather forecast, the daytime weather conditions on February1day are cloudy to sunny;

(2)PM2.5 is very harmful to human body. When inhaled into the human body, it will directly enter the bronchi, interfere with the gas exchange in the lungs, cause many diseases including asthma, bronchitis and cardiovascular diseases, reduce the visibility of the air and affect traffic;

(3) The weather features prone to haze are less precipitation, low temperature at night and low wind;

(4) Things that smog can do to improve air quality in life include green travel, bus travel and low-carbon life.

So the answer is: (1) cloudy to sunny; (two) caused by various diseases, low visibility, affecting traffic; (3) The temperature is low at night and the wind is small; (4) Green travel, bus travel and low-carbon life.