Beijing has issued an orange air pollution alert for the next three days starting from Friday. The orange alert is the second most severe in the country's four-tier air pollution warning system. The country's National Weather Bureau says the unfavorable weather conditions. Fireworks during the lantern festival as well as the resumption of production after the Spring Festival are all responsible for the air pollution. During this period the numbers of vehicles on the streets will be restricted and outdoor construction suspended. Some provinces in northern China have already issued orange or red alerts for heavy air pollution since Thursday.