According to state-run news agency Xinhua, a red smog alert is only issued if heavy pollution is expected to last longer than 72 hours.
China is the world's largest greenhouse gas emitter and aims to halve its emissions peak by 2030.
Most of the country's carbon emissions come from burning coal to heat homes and to fuel power plants, a practice that spikes during cold winter months.
Can China's most polluted city lead a green energy revolution?
CNN's Tim Hume, Bex Wright, Vivian Kam and Beijing intern Guanghong Hu contributed to this report