From the EPA: ” an extension of the public comment period on the Draft Risk and Exposure Assessment Reports for Nitrogen Dioxide (NO2) (73 FR 20045; April 14, 2008)”:

The EPA is extending the comment period that originally ends on May 1, 2008. The extended comment period will close on May 30, 2008. The EPA is extending the comment period to provide stakeholders and the public with adequate time to conduct appropriate analysis and prepare meaningful comments.

Under section 108(a) of the Clean Air Act (CAA), the Administrator identifies and lists certain pollutants which “cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare.” The EPA then issues air quality criteria for listed pollutants, which are commonly referred to as “criteria pollutants.’… Air quality criteria have been established for the nitrogen oxides (NOX) and NAAQS have been established for nitrogen dioxide (NO2), an indicator for NOX. Presently, EPA is reviewing the air quality criteria for NOX and the NAAQS for NO2.

The full release is available here.