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Rockbridge County, Virginia

Air Quality Index

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.

Reporting for February 11, 2019                  
Return to Main AQI Report
Monitoring Sites in
Rockbridge County
Air Quality RatingCritical
Air Quality Index
OzoneCarbon MonoxideSulfur DioxideNitrogen DioxidePM-2.5
(Lcl Acpt)
AQIppbAQIppbAQIppmAQIppbAQIppbAQIµg/m³ LC
Rockbridge County ††                        
Natural Bridge Station Good Ozone * 0 0 0                
The highest AQI value and associated average (1-hour, 8-hour, or 24-hour) that is responsible for the AQI rating are highlighted bold in the table.
PM-2.5 is measured at local pressure and temperature conditions.
†† - No AQI has been calculated for this county. This generally indicates that no data of any kind has been collected at any of the sites located in this county.
This may indicate a general data collection problem. Once any data collection problem is resolved, the data will be filled in and an AQI will be calculated (if possible).
‡ - There are not enough valid ozone hourly samples accumulated on February 11, 2019 to create eight-hour ozone averages.
* - There is no AQI associated with hourly ozone averages less than 0.125 ppm (125 ppb).

PLEASE NOTE:  Data in this table is collected from Virginia DEQ air monitoring sites, local agencies, and private monitoring networks. Site information is available for each specific site by clicking on the site 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 concentrations for each pollutant, the corresponding Air Quality Index (AQI) category, and the AQI ratings for each of the NAAQS pollutants that are measured real-time. 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 monitoring site within the Rockbridge County metropolitan area where pollutant levels are monitored by the Virginia DEQ.

Interpreting the AQI

Air Quality Index

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
in ppm
8hr Ozone
in ppm
8hr Carbon Monoxide
in ppm
1hr Sulfur Dioxide
in ppm
24hr Sulfur Dioxide
in ppm
1hr Nitrogen Dioxide
in ppm
24hr PM-2.5
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.