Congestion Pricing Could Bring Cleaner Air. But Maybe Not for Everyone.

When congestion pricing takes effect in New York City next month, officials say it will create an array of benefits: The system’s tolls will generate revenue for improving mass transit while prompting some drivers to avoid Manhattan, potentially reducing traffic and air pollution, as well as carbon emissions that contribute to climate change.

Some of those goals are already within sight: Devices that will monitor cars and send bills to drivers are in place, and the Metropolitan Transportation Authority, which will operate the system, has begun to detail the transit repairs and upgrades it plans to spend its windfall on.

For now, though, it is unclear how much the program will contribute to New York State’s ambitious goal of reducing greenhouse emissions 85 percent by 2050. And some people worry that less air pollution in some areas will be offset by more in others, despite efforts to keep that from happening.

According to an environmental assessment by the authority, congestion pricing could decrease air pollution overall in three boroughs: Manhattan, Brooklyn and Queens. The concern is that rerouted traffic could increase it in the Bronx and on Staten Island.

“It’s safe to say the direct air-quality benefits would be modest but measurable overall,” said Eric A. Goldstein, a senior attorney and New York City environment director at the Natural Resources Defense Council. The plan, he added, is worthwhile because of its benefits for public transit, whose health is crucial for luring people away from private vehicles.

“If you look at London and Stockholm, they had improved traffic, modest air quality, and jolts of adrenaline to their transportation systems,” he said, referring to similar programs in those cities.