Fine-particle pollution in Manhattan's toll zone ran 13% below trend in congestion pricing's first year

A plain before-and-after comparison would have overstated the toll's effect. PM2.5 had been falling across the region because of seasonal patterns and other policies, so the team compared monitors inside the zone with monitors outside it while controlling for weather and season ^[10]. The outside sites are the control. Whatever decline survives that subtraction is the part that happened only where most vehicles are now charged, in Manhattan south of 60th Street ^[5].

The subtraction is large. Against expected levels, PM2.5 inside the zone was 1.3 to 1.4 micrograms per cubic meter lower ^[11]. That is about half the largest raw decline recorded at any single representative site ^[18]. The researchers say the adjusted estimate is smaller than the raw site drops because it counts only the improvement attributable to the tolling program ^[11]. Set against the 13% figure, the change implies an expected concentration inside the zone of roughly 10 to 11 micrograms per cubic meter ^[19].

Traffic is the second line of evidence. Hourly counts from the Queens Midtown and Brooklyn Battery tunnels were generally lower in 2025 than in 2024, and the decline showed up in the morning and evening rush while the daily shape stayed similar ^[7]. The fall in vehicles entering the zone broadly tracked the pollution estimate ^[12]. Pollution and traffic falling together, in the same place and at the same busy hours ^[7][13], is the pattern a causal effect would produce. It is still a correlation. The study's traffic record comes from two tunnel crossings, read alongside 15 air monitors and satellite nitrogen dioxide observations ^[6].

The design rests on one assumption: that monitors outside the zone were untouched by the toll. The researchers looked at a possible rise in PM2.5 at two monitoring sites just outside the boundary ^[15]. If traffic diverted around the zone raised readings at sites used as controls, the inside-outside gap would overstate the toll's effect.

The paper measured concentrations. It did not evaluate health benefits; fine particles are linked to cardiovascular and respiratory disease, and lower exposure is generally expected to improve outcomes ^[14]. Co-author Daniel Westervelt, an associate research professor at Columbia's Lamont-Doherty Earth Observatory ^[3], kept his summary close to the measurement. "For the most part, the program appears to be working," he said. "It reduced particulate pollution inside the congestion zone by a modest amount." ^[2]

First author Polina Goldberg, who began the work as an undergraduate in Lamont's summer internship program ^[3], explained why the team waited for twelve months of data. "A full year of data helps us see whether changes in air quality remain consistent across all seasons and different weather conditions," she said ^[16]. "Other cities have been waiting to see what happens in New York before they consider anything similar, so we wanted to get the analysis right rather than fast." ^[17]