PJM’s marginal emissions graph reflects the marginal emissions rates of carbon dioxide (CO2), nitrogen oxides (NOx) and sulfur dioxide (SO2). The marginal emissions are the emissions caused by producing the last megawatt of energy on the system. Any variations in dispatch patterns to ensure system-wide reliability may change the set of marginal units. Therefore, a significant change in dispatch could shift the marginal generating unit, and thus, the marginal emission rates accordingly.
The hourly emissions graph compares the average hourly total emissions for each of the three pollutants for all fuel types over a rolling 24 hours. Average emissions rates are used for the generation resources and these rates do not reflect the specific operating output point of the generator, and as such these values are approximate.
This information is based on annually reported average data from electric generators within the PJM footprint. PJM does not receive real-time emissions data from plants.