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Information On Pollutants

  • GHGs
  • NOx
  • SO2
  • Mercury
  • Lead

 HERO—About Greenhouse Gas Emissions

Greenhouse gases (GHGs) are gases that trap heat in the atmosphere by absorbing and emitting thermal radiation from the sun.

These include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases. Some greenhouse gases, such as CO2, are emitted to the atmosphere through both natural processes and human activities. Other greenhouse gases (e.g., fluorinated gases) are created and emitted solely through human activities.


Carbon dioxide enters the atmosphere through the burning of fossil fuels (oil, natural gas, and coal), solid waste, trees and wood products, etc. Carbon dioxide is also removed from the atmosphere (or “sequestered”) when it is absorbed by plants as part of the biological carbon cycle.

CO2 equivalents are calculated based on the Global Warming Potential (GWP) ( of different gases. Global-warming potential (GWP) is a relative measure of how much heat a greenhouse gas traps in the atmosphere compared to how much heat is trapped by CO2.

The GWP depends on the absorption of infrared radiation by a given species, the frequency of light wavelengths that are absorbed, and the atmospheric lifetime of the species. For example, the GWP of methane for the 20-year time horizon is 72, which means that over the course of 20 years a kg of methane will trap 72 times more heat in the atmosphere than a kg of CO2.

In HERO's case, CO2 equivalents reported represent the emissions from three main GHGs: CO2, methane (CH4), and N2O. The mass of emissions is multiplied by the 20-year GWP for each gas.

Worldwide, emissions of greenhouse gases from human activities increased by 26 percent from 1990 to 2005. Emissions of carbon dioxide, which account for nearly three-fourths of the total, increased by 31 percent over this period.


Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices and by the decay of organic waste in municipal solid waste landfills.

 What can I do to lower emissions of greenhouse gases?

To reduce GHG emissions, use HERO to find out when emissions from electric power generation are high or low.

HERO uses real-time market pricing of electricity to estimate the marginal fuel type that is being used to produce electricity at any given time. This could be nuclear or renewable, coal, natural gas, or fuel oil. Each fuel type results in a different set emission rates for all pollutants. Learn more about marginal fuel type in HERO's About section.

HERO was made to help you lower the emissions from your electricity use. You can take note of when emissions are typically high or low, and use these patterns to reduce your emissions by changing the timing of your electric load. You can set timers for certain appliances or battery chargers so that these electric loads occur when emissions are low.

 Related Links:

* EPA: Greenhouse Gas Emissions
* EPA: CO2
* EPA: Methane
* Global Warming Potential Calculation
* EPA: Climate Change Indicators in the USA
* Greenhouse Effect Picture
* Sources of CO2 Graphs
* Sources of Methane Picture
* Sources of SOx Picture
* Sources of N2O Picture