On January 22, 2010, the EPA established a new one-hour National Ambient Air Quality Standard (NAAQS) for Nitrogen Dioxide (NO2) at 100 parts per billion (ppb) (approximately 189 ug/m3). The new 1-hour standard is calculated as the three-year average of the 98th percentile of daily maximum one-hour average concentrations of NO2. Studies have shown increases in respiratory symptoms and hospital visits related to short-term exposure to high levels of NO2. The new 1-hour NO2 standard is a primary standard which aims to protect public health associated with short-term exposure to NO2 including respiratory effects. The EPA is separately reviewing the secondary NO2 standard, which aims to protect public welfare. Despite the new standards, the existing annual NO2 standard of 53 ppb (100 ug/m3) remains unchanged.
With the new short-term NO2 standard, the EPA is also requiring three levels of monitors to be installed in urban areas: near major roadways, at a community-wide level, and in susceptible and vulnerable communities. For each city with a population over 500,000, at least one near-road monitor will be required at major roads within 50 meters of the closest traffic lane. Currently, there are over 400 monitors for NO2 operating in the United States, mostly community-wide monitors, and these show all areas in the United States are below the annual standard of 53 ppb. Available monitoring data from community-level monitors during the period of 2006 through 2008 show that almost all counties meet the new one-hour NO2 standard as well. However, the concentrations are expected to be much higher near major roadways where mobile sources contribute to approximately 60% of NO2 emissions. The EPA expects to initially designate the attainment status of areas by January 2012, but then re-designate areas three years later based on new monitoring data once the new network of monitors has been in place.
Impacts on PSD Permit Actions
The final rule will be effective April 12, 2010, 60 days after publication in the Federal register on February 9, 2010. With the promulgation of the new NO2 NAAQS, new or modified major sources in attainment areas will need to demonstrate compliance with the new 1-hour NO2 NAAQS (in addition to the existing NAAQS) as part of PSD air quality analyses completed. EPA has not yet defined or even proposed Significant Impact Levels or Class I / Class II Increment Standards associated with the new 1-hour average NO2 NAAQS, so additional guidance will need to be provided by the EPA and states to confirm specific protocols to follow in conducting the 1-hour NO2 air quality modeling analyses. Demonstrating compliance with the 1-hr NO2 NAAQS at facilities with certain types of sources, such as large diesel-driven emergency generator engines located near buildings and within close proximity to the fenceline, may be problematic. In these situations, the potentially high short-term impacts predicted in the modeling may require that engines with lower emission profiles be evaluated or that additional controls and/or stack configurations for these sources be considered.
For more information regarding the current NO2 standards and proposed changes visit http://www.epa.gov/air/nitrogenoxides/. The proposal in the Federal Register can be accessed at: http://www.epa.gov/air/nitrogenoxides/actions.html.