This document summarizes the new 1-hour nitrogen dioxide (NO2) National Ambient Air Quality Standard (NAAQS) and modeling requirements. Key points include: 1) The new 1-hour NO2 NAAQS is 188 micrograms per cubic meter (100 parts per billion), assessed as a 3-year average of the 98th percentile of daily maximum 1-hour concentrations. The annual NAAQS is still in place. 2) Air quality modeling to demonstrate compliance must use AERMOD and either 5 years of National Weather Service data or 1 year of on-site data. 3) PSD modeling should compare project emissions to significant impact levels to determine if a multi-source