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Regional air emissions 2016: long-term reduction trends continue

Since 2001, SO2 down 98%, NOx down 73%, CO2 down 29%

Driven primarily by a decrease in coal and oil generation, regional emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), and carbon dioxide (CO2) declined between 2015 and 2016, according to data compiled for the 2016 ISO New England Electric Generator Air Emissions Report. The year-over-year declines continued long-term reductions in the emissions generated by the region’s power plants.

Year-over-year changes: 2016 vs. 2015

The below tables summarize the year-over-year changes for total system emissions (the amount of system emissions) and emission rates (the pounds of emissions given off, on average, with every megawatt-hour [MWh] of electricity produced). This is akin to comparing how many gallons of gasoline a car used versus its miles per gallon (MPG). Between 2015 and 2016, the region saw declines in both emission amounts and rates for SO2, NOx, and CO2.

2015 and 2016 New England system emissions (ktons) and emission rates (lb/MWh)

Several key factors contributed to the decreases between 2015 and 2016:

  • Sharp decreases in coal- and oil-fired generation—A warmer winter contributed to decreases in generation from coal and oil resources in 2016. Coal generation fell by 1,330 gigawatt-hours (GWh), or 34 percent, while oil generation fell by 999 GWh, or 51 percent.
  • Slight decline in overall energy generation—Overall, generation in New England was 105,570 GWh, a 2% decline over the previous year.
  • Significant increases in production from non-emitting resourcesNuclear generation increased by 855 GWh, or 2.7%, over 2015, while grid-scale solar and wind resources together increased production by 546 GWh, or 21%.

The chart below shows each fuel type’s contribution in 2016 by month.

2016 ISO New England monthly generation by fuel type (% MWh, MWh)

Long-term trends: 2001–2016

Total emissions for SO2 and NOx declined from 2001 to 2016 by 98% and 73%, respectively, while CO2 emissions decreased by 29%. The below table and graphs from the emissions report show the total amount of air emissions on an annual basis in kilotons (kTons), as well as the emissions rates over the last decade.

Annual Emissions of NOX, SO2, and CO2, 2001 to 2016 (kilotons)

New England system annual emissions of NOX, SO2, and CO2, 2007 to 2016 (ktons)

New England system annual average NOX, SO2, and CO2 emission rates, 2007 to 2016 (lb/MWh)

A shifting fuel mix

The type and magnitude of a generator’s emissions are directly linked to the type of fuel that powers it, and the fuel mix used to produce New England’s electricity has changed significantly over the past decade.

Percentage energy generation by fuel type, 2007 compared with 2016

Natural gas-fired resources account for the vast majority of new generators built in New England since 1997. This ongoing trend to meet electricity needs with higher-efficiency, lower-emitting gas-fired generators instead of oil- and coal-fired generators has been the biggest contributor to the long-term decline in regional emissions. Transmission system upgrades have further reduced the need to run older, less efficient oil and coal units.

The region’s increasing development of wind, solar, and other zero-emission resources will further contribute to reducing greenhouse gases. As of August 2017, about 55% of all proposed projects in the generation interconnection queue are wind-power resources.

More imported electricity

Since 2004, lower-priced electricity from outside New England has increasingly flowed in to serve regional demand. This external generation, which served 17% of New England’s energy needs in 2016, doesn’t count toward regional air emissions.

Less demand for electricity from the regional power system

Since about 2005, annual regional demand for wholesale electricity has been declining, and with it, so has electricity generation. The economic downturn and slow recovery helped dampen electricity consumption. Several long-term factors have also been at work to reduce the amount of power consumers pull from the grid:

  • Energy-efficiency (EE) investment—The New England states are national leaders in implementing EE measures, such as the use of more efficient lighting, appliances, cooling, and building operation. These EE programs are having a noticeable effect. The ISO’s EE forecast projects the $1.1 billion that the states invest annually from 2021 to 2026 will save an average of 1,923 GWh each year for the region and slightly decrease the growth of gross regional energy usage from 1.0% to -1.0%. Growth in peak demand, the periods of highest electricity usage, will slow from 1.1% to -0.1%.
  • Demand resources—Like power plants and other supply resources, demand resources are competitive assets that help meet New England’s electricity needs. But instead of generating power, they reduce the amount of power they’d normally pull from the grid. EE measures are an example of passive demand resources, while active demand resources include practices like powering down machines or switching to an on-site generator. (Learn more.)
  • Distributed generation—The growing numbers of small-scale solar power systems are one example of how more and more New Englanders are supplying some or all of their own power. The ISO’s forecast of regional solar photovoltaic (PV) power predicts that PV installations in the region will more than double by 2026.