Since 1993, ISO New England has produced an annual report on generator air emissions—a comprehensive analysis of the emissions produced by the region’s generation fleet and a review of relevant system conditions. The ISO also publishes real-time emissions estimates on ISO Express.
Air emissions from regional generators have fallen dramatically since the early 2000s. From 2001 to 2021, annual emissions for sulfur dioxide (SO2), nitrogen oxides (NOX), and carbon dioxide (CO2) declined by 99%, 80%, and 41%, respectively.
Source: 2021 ISO New England Electric Generator Air Emissions Report
However, several factors—including increasing oil-fired generation during winter cold snaps due to natural gas pipeline constraints and the retirement of nuclear generation—have contributed to some recent year-over-year increases. Learn about the changes between 2020 and 2021, for example, in the 2021 ISO New England Electric Generator Air Emissions Report.
The table below summarizes annual emissions for 2021 as well as emission rates (the pounds of emissions given off, on average, with every megawatt-hour of electricity produced). This is akin to comparing how many gallons of gasoline a car used versus its miles per gallon. The table includes figures for emissions from native generation (electricity produced by power plants located in New England), as well as data on emissions associated with native generation plus electricity imported from other regions.
Native generation | 2021 emissions (kilotons) | Change from 2020 | 2021 emission rate (lbs./MWh) | Change from 2020 |
---|---|---|---|---|
NOx | 12.44 | +2.9% | 0.24 | -4.0% |
SO2 | 2.11 | +12.2% | 0.04 | 0.0% |
CO2 | 33,439 | +7.8% | 658 | +0.6% |
Native generation and imports | ||||
CO2 | 34,555 | +4.2% | 574 | +2.4% |
Source: 2021 ISO New England Electric Generator Air Emissions Report
Several factors have played a role in the overall reduction of generator air emissions:
Two overarching factors are largely responsible for year-over-year changes in emissions:
Source: 2021 ISO New England Electric Generator Air Emissions Report
Some emerging factors could push the ISO to rely more on higher-emitting, less efficient resources to meet regional electricity demand: