The U. S. Environmental Protection Agency (EPA) has provided a scale called the Air Quality Index (AQI) for rating air quality. This scale is based on the National Ambient Air Quality Standards (NAAQS) and is described in the Code of Federal Regulations, Part 58, Appendix G. This report is based on the AQI standards. More information on the AQI can be found on the EPA's AirNow web site.
PLEASE NOTE: Data in this table is collected from Virginia DEQ air monitoring sites, local agencies, and private monitoring networks. Site specific information is available for each metropolitan area by clicking on the metropolitan area name. This data has not been verified by the Virginia DEQ or the responsible entity and may change. While this is the most current data, it is not official until it has been certified by the appropriate technical staff. This table is updated hourly. Click here for information about all the monitoring sites.
The table above lists the current peak concentration for the critical pollutant, the corresponding Air Quality Index (AQI) category, and the AQI ratings for each of the NAAQS pollutants that are measured real-time. The critical pollutant is the pollutant with the highest AQI rating measured in the area. The table is updated each hour and covers the period from midnight through the indicated ending time for today's data or from midnight to midnight on other days. Listings are provided for each metropolitan area where pollutant levels are monitored by Virginia DEQ.
Each NAAQS pollutant has a separate AQI scale, with an AQI rating of 100 corresponding to the concentration of the Federal Standard for that pollutant. Additional information about the AQI and how it can be used is available from the EPA's AirNow web site.
Place your mouse pointer over the scale displayed above to view information about the Air Quality Index, and each of the rating levels.
The actual index calculation is different for each parameter measured and is specified by the EPA. The following table shows the various breakpoints used in calculating the AQI.
|AQI Breakpoint Definitions|
|AQI Range||1hr Ozone
|8hr Carbon Monoxide
|1hr Sulfur Dioxide
|24hr Sulfur Dioxide
|1hr Nitrogen Dioxide
in µg/m³ LC
|0 - 50||Not Defined||0 - 0.054||0 - 4.4||0 - 0.035||Not Defined||0 - 0.053||0 - 12.0|
|51 - 100||Not Defined||0.055 - 0.070||4.5 - 9.4||0.036 - 0.075||Not Defined||0.054 - 0.1||12.1 - 35.4|
|101 - 150||0.125 - 0.164||0.071 - 0.085||9.5 - 12.4||0.076 - 0.185||Not Defined||0.101 - 0.36||35.5 - 55.4|
|151 - 200||0.165 - 0.204||0.086 - 0.105||12.5 - 15.4||0.186 - 0.304||Not Defined||0.361 - 0.649||55.5 - 150.4|
|201 - 300||0.205 - 0.404||0.106 - 0.200||15.5 - 30.4||Not Defined||0.305 - 0.604||0.65 - 1.249||150.5 - 250.4|
|301 - 400||0.405 - 0.504||Not Defined||30.5 - 40.4||Not Defined||0.605 - 0.804||1.25 - 1.649||250.5 - 350.4|
|401 - 500||0.505 - 0.604||Not Defined||40.5 - 50.4||Not Defined||0.805 - 1.004||1.65 - 2.049||350.5 - 500.4|
|500+||Not Defined||Not Defined||Not Defined||Not Defined||Not Defined||Not Defined||Not Defined|
PLEASE NOTE: This data has not been verified by the Virginia DEQ and may change. This is the most current data, but it is not official until it has been certified by our technical staff. Data is collected from Virginia DEQ ambient monitoring sites and may include data collected by other outside agencies. This data is updated hourly. All times shown are in local standard time unless otherwise indicated.