August 5, 2022. The transition of the Metropolitan Transportation Authority (MTA) bus fleet in New York City to cleaner fuels and engines was followed by declines in air pollution, particularly nitrous oxide. The study was led by scientists at Columbia University Mailman School of Public Health, Columbia Irving Medical Center, and Drexel University Dornsife School of Public Health. The findings are published in the Journal Of Exposure Science And Environmental Epidemiology.
Beginning in 2000, the MTA began deploying compressed natural gas (CNG), hybrid electric, and low-sulfur diesel buses to reduce urban air pollution. In addition, existing buses were retrofitted with diesel particulate filters.
The researchers examined air pollution concentrations in 9,670 300mx300m grid cell areas across the five boroughs, as measured by the New York City Community Air Survey, between 2009 and 2014, as the MTA transitioned its fleet to clean buses. Data were assessed alongside depot- and route-specific data on the fleet transition and bus traffic sourced from publicly-available data and FOIL (Freedom of Information Law) requests.
Shifts toward clean bus service were associated with slower declines in BC concentration. This finding may be explained by the fact that hybrid diesel buses can produce more particulate matter than their conventional counterparts due to their smaller engine size. Alternately, it may be because the study was better attuned to measures of fresh combustion emissions such as NO, for which exposure rapidly decreases with distance to busy roadways.