Elevated tropospheric ozone is a photochemical product of natural and anthropogenic volatile organic chemical emissions, and nitrogen oxides, which are mainly the product of fuel combustion. Examination of fossil-fueled electrical generating unit (EGU) operations before and during eastern seaboard heat wave events, which also tend to produce violations of the 8-hour ozone standard, reveals substantial daily as well as hourly variations in NOx emission profiles.

In general, baseload coal-fired units, many of which lack adequate NOx control technology are ramped up as load increases. Also as load increases, intermittently used residual oil-burning load-following boilers are deployed. As electric supply must always equal demand, intraday hourly peaks are generally met by generation from high NOx -emitting quick starting combustion turbines.

These phenomena are illustrated through comparison of operating profiles on an average day in June 2005 and the then record demand day of July 26, 2005, which also saw numerous ozone standard violations throughout the region. While peak hourly generation on the PJM power grid mid-Atlantic sector on the two days was 31,162 MW and 58,509 MW, respectively, NOx emissions from �peaking� EGUs in the 6-state Maryland-Connecticut region increased 145% from 492 to 1,202 tons, with a rate increase of 41% from 1.50 lbs NOx / MWh to 2.11 NOx / MWh.

Many of these high-emitting units have been in service since the 1970's and even earlier. While lower emitting units of more modern vintage also are deployed in response to rising demand, their contributions to elevated NOx emissions are miniscule.