This bulletin is updated hourly with information calculated on data readings averaged over 8 hours for carbon monoxide, 24 hours for PM2.5 and 1 hour for PM10, ozone, nitrogen dioxide, sulfur dioxide and visibility reduction. Detailed information on the calculation of the index is available below.
Data for a given hour are available at 30 minutes after the following hour. For example, data for 9 am-10 am is available at 10.30 am. See below for more information about station summaries, 'not available' and 'offline' reports.
Update 28 February 2014: EPA has changed the way some of our data (including CO and SO2) is displayed in the air quality table. It is possible for CO concentrations to be reported by our equipment as a negative. To avoid any confusion, EPA is now rounding all readings back to 0. The raw data in our systems will remain as originally collected.