New England power plant air emissions increased in 2021

New England's power plants collectively emitted greater amounts of key air emissions in 2021 than in the year before, according to a report by the region's electric grid operator. Factors included the weather, decreases in power imported from outside the region, and increased reliance on coal and oil-fired generation.

The 2021 ISO New England Electric Generator Air Emissions Report provides "a comprehensive analysis of New England’s native electric generator air emissions (nitrogen oxides [NOX], sulfur dioxide [SO2], and carbon dioxide [CO2]), along with CO2 emissions associated with imported energy, and a review of relevant system conditions."

New England has significantly reduced the air emissions associated with its electric power sector over the past decades. According to the report, total average air emissions from "native generation" (in-region) have decreased overall during the 10-year span from 2012 through 2021: NOx by 39%, SO2 by 87%, and CO2 by 20%. The report credits the decline in emissions over this period to "shifts in the regional generation mix, with imports and wind generation offsetting decreases in coal-fired generation." 

Looking farther back to cover the 20-year span from 2001 through 2021, NOx emissions fell by 80%, SO2 emissions fell by 99%, and CO2 emissions fell by 41%. Summarizing these two decades of change, ISO-NE says, "The increased use of highly efficient natural-gas-fired generators, mandated use of lower-sulfur fuels, retirements of coal- and oil-fired generation, increasing amounts of wind and solar generation, and higher net energy imports have all contributed to the trend."

But on a year-over-year basis, emissions increased in 2021 relative to 2020 according to the grid operator. For native generation, NOx emissions grew by 2.9%, SO2 emissions grew by 12.2%, and CO2 grew by 7.8%. 

ISO-NE attributes the region's recent backsliding on emissions to several factors, including increased demand for native generation (due to a 20% reduction in imports), weather (warm summer, cold winter), and "the resource mix":

Coal- and oil-fired generation had year-over-year increases of 281% and 53%, respectively. Resources fueled by coal or oil produced more power than usual during colder weather in January and February 2021, and production by oil-fired resources also increased during hot weather in June and August. These resources, which have higher emission rates than plants fueled by natural gas, often contribute generation during peak energy demand periods in the summer, or when winter heating demand limits the availability of natural gas or drives up its price.

The grid operator expects continued growth in demand for electricity, as transportation and heating increasingly become powered by electricity.