The rains set off dangerous mudslides, inundated homes and destroyed bridges
The municipal weather centre said humidity and a lack of wind would mean the smog will linger for another two days, before a cold front arrives on Wednesday, Xinhua reported.
On Sunday, the reading for PM2.5, airborne particles smaller than 2.5 microns in diameter, hit 274 micrograms per cubic metre in most parts of the capital.
Under the orange weather alert mechanism, industrial plants are required to reduce or shut down production; construction sites should stop the transportation of materials and waste while heavy-duty trucks are banned from the roads.
The municipal environment watchdogs have reinforced checks of discharge from coal-fired plants, outdoor barbecues and burning.