Beijing and its neighboring cities will start using uniform criteria when they issue pollution alerts by the end of March, the capital's environmental protection bureau said on Sunday.

Alerts will be categorized by Air Quality Index (AQI) readings. A red alert will be issued when the daily average AQI is forecast to rise above 500 for a day or longer. A red alert can also be issued when the daily average is forecast to climb above 200 for four straight days or longer, or when the daily average exceeds 300 for two days or longer.

Beijing, Tianjin and Hebei Province employ different criteria for issuing pollution alerts. For instance, in Beijing, a red alert is issued when AQI exceeds 200 for more than three days, while in Tianjin and Hebei, a red alert is triggered only when AQI exceeds 500 for at least one day.

The uniform alert raises the criteria for issuing an orange alert or a red alert for Beijing while tightening air pollution regulation for cities in Hebei, said Liu Wei, deputy head of the emergency response office at the environmental protection bureau.

Response measures to alerts will stay the same except that each city can decide if primary and middle schools should be temporarily closed.

The uniform alert system will first apply to Beijing, Tianjin and four cities in Hebei and then expand to a larger area.

Beijing has issued two red alerts for smog since the start of this winter, prompting closures of schools and bans on outdoor construction. Tianjin and Hebei also issued their first air pollution red alerts in December.