"I couldn't see the tall buildings across the street this morning," said a traffic coordinator at a busy Beijing intersection who gave only his surname, Zhang. "The smog has gotten worse in the last two to three years. I often cough, and my nose is always irritated. But what can you do? I drink more water to help my body discharge the toxins."

The city's air quality is often poor, especially in winter when stagnant weather patterns combine with an increase in coal-burning to exacerbate other forms of pollution and create periods of heavy smog for days at a time. But the readings early Thursday for particles of PM2.5 pollution marked the first ones of the season above 500 micrograms per cubic meter.