When Dong Yingli first opened her meat skewers restaurant in Beijing six years ago, her chefs cooked over an uncovered grill, with fans blowing clouds of pungent smoke from the sidewalk into the middle of the street.

Elsewhere in the capital, four coal-fired power plants belched emissions into smoggy skies, while countless steel and cement factories in neighboring provinces emitted millions of tons of cancer-causing particles.

Now, more than a year since Premier Li Keqiang declared war on pollution, Beijing's massive anti-smog fight is transforming the metropolis in ways both big and small. Still, as was evident on several days over the past week, when a thick gray pall filled the streets, the Chinese smog battle is far from won.

Authorities in Beijing are shutting down coal-fired power plants within the city limits and have tried to reduce vehicle exhaust by forcing many residents to wait years for a license plate.

In the neighborhood where Dong runs her restaurant, inspectors have become a regular sight as they make sure vendors have installed thousands of dollars' worth of ventilation and filters. Though Dong doesn't think her business had much to do with the state of Beijing's air, she says the extra enforcement in general has made breathing easier.

"The environment has got a lot better here," Dong said at a sidewalk table on a recent smoggy evening. "There used to be so much smoke here, it was hard to even see. This needed to be done."

Despite the reforms, official figures show that Beijing's average density of PM2.5 — harmful particles that are small enough to enter the bloodstream — was nine times the World Health Organization air quality safety level in the first three months of the year.

That still marked a 19 percent drop from pollution levels a year before.

The city has shown it can bring back days-long stretches of blue skies for high-profile events such as last year's Asia-Pacific Economic Cooperation group meeting, but only by wielding the toughest of measures, such as encouraging residents to leave town and closing factories more than 120 miles away.

Keeping the skies clean on a daily basis will require more permanent fixes, said Li Xiang, of the city's Environmental Protection Bureau.

"Changing air pollution is a long-term project," Li said. "In other cities, like London and Los Angeles in the US, it took about 50 years to reduce air pollution and show significant change. ... Beijing has made significant improvements, but meeting people's expectations will take some time."

Lax enforcement of the new environmental restrictions is a clear obstacle to cleaning up the capital's air.

For example, although Beijing has banned open-air barbecues within its Fourth Ring Road, clouds of skewer smoke are common sights in the twisting alleyways and roads throughout the city center. Many drivers also regularly flout restrictions requiring cars to stay off the roads on certain days.