Regional air emissions 2015: slight year-over-year increase in CO2 levels; long-term reductions remain significant 
Wednesday, February 1, 2017 at 8:53AM
ISO New England in Industry News & Developments, energy efficiency, environment, natural gas, new england states, oil, renewable resources, solar

Since 2001, SO2 down 95%, NOx down 68%, CO2 down 24%

The retirement of Vermont Yankee Nuclear Power Station and the continuing trend of increased oil-fired generation in New England were factors in a slight increase in carbon dioxide (CO2) emissions in 2015 compared to 2014, as well as slowing year-on-year declines, as reported in the 2015 ISO New England Electric Generator Air Emissions Report, issued January 2017. However, significant retirements of coal-fired generation contributed to the region’s continuing long-term reductions in the emissions generated by the region’s power plants.

Year-over-year changes: 2015 vs. 2014

Table 1-1 from the emissions report summarizes 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). For both emission amounts and rates, SO2 was down significantly, NOx dropped, and CO2 was up slightly.

Several key factors contributed to the changes between 2014 and 2015:

Charts and graphs from the emissions report below show each fuel type’s contribution by month, as well as changes in fuel types and emission rates over recent years.

Long-term trends: 2001–2015

Total emissions for sulfur dioxide (SO2) and nitrogen oxides (NOx) declined from 2001 to 2015 by 95% and 68%, respectively, while CO2 emissions decreased by 24%. This table and graph from the emissions report show the total amount of air emissions on an annual basis in kilotons (kTons).

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.

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 January 2017, about 44% of all proposed projects in the generation interconnection queue are wind-power resources.

Tighter emissions controls

Implementation of emission controls, as required by federal regulations and stringent, leading-edge requirements set by the New England states, have helped reduce emission levels from coal-fired resources when they do run, contributing to the striking long-term decrease in SO2, in particular.

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:

For more information

To learn more about the ongoing evolution of the grid and challenges associated with a changing fuel mix, read ISO New England’s Regional Electricity Outlook.

For information on winter power system performance, see “Winter 2015/2016 recap: New England power system performed well and prices remained low” and “2016/2017 winter outlook: sufficient electricity supplies expected.”

Article originally appeared on ISO Newswire (
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