By Amethyst Cavallaro
Online Editor, Power Engineering
The U.S. Environmental Protection Agency (EPA) announced its adjustments to the national air quality standards on Sept. 21 after a mandatory five-year review process. The National Ambient Air Quality Standards (NAAQS) address fine and coarse particle pollution, also known as particulate matter (PM).
The final action changes the 24-hour allowance for fine particulates, such as those emitted from coal-fired generation stacks, from 65 micrograms of particles per cubic meter (µg/m3) of air to 35 µg/m3. EPA said this measure protects people from short-term exposure to fine particles. The annual standard will remain the same at 15 µg/m3.
According to EPA data, under the previous standards, no counties violated the 24-hour fine particles standard at 65µg/m3 during 2001-2003 testing. The new standard cuts the emission allowance almost in half, and 69 counties will not meet the 35 µg/m3 rule, according to 2003-2005 EPA monitoring data.
“This will not be an emissions standard for every plant,” Carl Weilert, of Burns & McDonnell, said in an interview with Power Engineering. Only the power plants that are located in non-attainment counties may be affected. Even then, not every power plant in that area will have to put up a baghouse. The state government must present computer-modeling data for the non-compliant county and show the particle matter, usually SO2 or NOx for power plants, is coming from the power plant source. States must take into account all potential sources, such as vehicles or factories, instead of singling out power plants.
The annual allowance of fine particulate matter will remain the same at 15 µg/m3. EPA monitoring data showed progress in troubled areas under this standard. In the 2001-2003 testing period, 37 counties were not in compliance with the annual standard. Since that time, 20 counties have come into compliance.
Weilert said the 24-hour standard has always been the more difficult to meet and computer modeling has usually reflected its monitoring data instead of the annual data. Additionally, he predicted that this 24-hour standard will now be the “controlling factor” in pushing the EPA to adjust its Clean Air Interstate Rules (CAIR) to include more stringent emission caps for states.
In the past, the EPA’s approach has been to control the precursors of particulate matter pollution, including SO2 and NOx. States may evaluate the air monitor data and see that the precursors may be coming from other sources across state boundaries. This might lead the EPA to lower the allowable levels under a national standard (CAIR) that would apply to all states instead of to the counties that have non-attainment levels. This process might lead to what Weilert called “CAIR 2” with new standards and new regulations for power plants to meet.
The most likely emission technology to be used would be retrofits using selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR) for NOx emissions and flue gas desulphurization (FGD) for SO2.
But power plants will have plenty of time to plan for the future. The process has just begun with monitoring and computer modeling as the next step. Then, states will need to come up with a plan to bring down their emissions as they see fit.
The EPA said the states must meet its revised standards by 2015, with a possible extension to 2020, depending on local conditions and the availability of controls.
The EPA also issued revisions on monitoring particle pollution. The EPA said changes focus on retaining but reshaping existing monitoring networks for “criteria pollutants.” The six pollutants the EPA monitors are ground-level ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, particle pollution and lead.
The rule will change the locations of some types of monitors, add 75 new multi-pollutant monitors (some with real-time air quality measurements) and allow states to shut down unneeded monitors for some pollutants. Of the new monitoring sites, 55 will be in urban areas and 20 in rural areas. The EPA said this would enhance their understanding of how pollution travels and the difference in air quality in urban and rural areas.
Some of the new monitors will provide hourly measurements in real-time for PM, while others will sample the air over a 24-hour period and require laboratory processing of the samples. The monitors will be able to detect SO2 pollution at lower levels than existing monitors and will selectively monitor certain categories of NOx that contribute most to PM formation.
Additional information about the national air monitoring network and its fine PM testing is available at http://www.epa.gov/ttn/amtic/amticpm.html.
See the images below for maps created by the EPA of the non-attainment areas under the new and old standards.
Non-attainment Counties Under Old Standards
Non-attainment Counties Under New Standards