The drop indicated that the government’s antipollution campaign — first announced in 2013 but accelerated last year for regions around the capital — has begun to show results.

Even so, pollution levels fell less precipitously or rose elsewhere, suggesting that a concerted effort last fall to shift heating to natural gas from coal may have simply shifted the harmful effects to regions far from the capital.

In the northern province of Heilongjiang, on the border with Russia, pollution levels rose 10 percent. In a statement with its analysis, Greenpeace argued that the results demonstrated the need for more government action, noting that nationwide the drop in pollutants was only 4 percent.

“China’s national air pollution action plan has brought massive reductions in pollution levels and associated health risks, but policies favoring coal and heavy industry are holding back progress,” Huang Wei, one of the organization’s campaigners, said in the statement.

But in Beijing, where pollution levels are tracked as closely as property prices are in Hong Kong, London or New York, the respite from eye-watering, throat-scratching smog has nonetheless been welcomed. Only a year ago the pollution was so bad on some days that schools were closed and flights were canceled.