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.

Interpreting the AQI

Reporting for February 18, 2019 as of 3:53 pm PST
Metropolitan Area or Non-Metropolitan County		Air Quality Rating	Critical Pollutant	Air Quality Index
				Ozone				Carbon Monoxide		Sulfur Dioxide		Nitrogen Dioxide		PM-10 (Std Cond)		PM-2.5 (Lcl Acpt)		PM-2.5 (Lcl Cond)
				1-Hour		8-Hour		8-Hour		1-Hour		1-Hour		24-Hour ⁽²⁾		24-Hour ⁽²⁾		24-Hour ⁽²⁾
				AQI	ppb	AQI	ppb	AQI	ppm	AQI	ppb	AQI	ppb	AQI	µg/m³ (25° C)	AQI	µg/m³ LC	AQI	µg/m³ LC
Clark County -- Region 1
	Boulder City	Good	Ozone	*	44	37	40							3	3.52
	Greater Las Vegas	Good	Ozone	*	44	37	40	2	0.157	##	-0.1	21	22.2	6	6.37			9	2.26
	Jean	Good	Ozone	*	44	36	39							1	1.46			3	0.70
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-10 is measured at standard pressure and temperature conditions.
PM-2.5 is measured at local pressure and temperature conditions.
⁽²⁾ - This is an average since midnight for the current day and does not represent an entire day of data. The reported overall AQI category could change and will not be complete until all the data for the calendar day is polled and processed and could be further subject to later change by the data validation process.
* - There is no AQI associated with hourly ozone averages less than 0.125 ppm (125 ppb).
## - No AQI is defined for negative values.

PLEASE NOTE: Data in this table is collected from DAQ 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 DAQ 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 DAQ.

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-10 in µg/m³ (25° C)	24hr PM-2.5 in µg/m³ LC	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 - 54	0 - 12.4	0 - 12.4
51 - 100	Not Defined	0.055 - 0.070	4.5 - 9.4	0.036 - 0.075	Not Defined	0.054 - 0.1	55 - 154	12.5 - 35.4	12.5 - 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	155 - 254	35.5 - 55.4	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 - 0.64	255 - 354	55.5 - 150.4	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 - 1.24	355 - 424	150.5 - 250.4	150.5 - 250.4
301 - 400	0.405 - 0.504	0.201 - 0.2011	30.5 - 40.4	Not Defined	0.605 - 0.804	1.25 - 1.64	425 - 504	250.5 - 350.4	250.5 - 350.4
401 - 500	0.505 - 0.604	Not Defined	40.5 - 50.4	Not Defined	0.805 - 1.004	1.65 - 2.04	505 - 604	350.5 - 500.4	350.5 - 500.4
500+	Not Defined	Not Defined	Not Defined	Not Defined	Not Defined	Not Defined	605 - 4999	500.5 - 999.9	500.5 - 999.9

The AQI for ozone is based on either the peak eight-hour running average since midnight OR the peak one-hour measurement since midnight. When calculating air quality for the current day, the Clark County DAQ uses a surrogate 8-hour average based on the current hourly average.
The AQI for carbon monoxide is based on the peak eight-hour running average since midnight.
The AQI for sulfur dioxide is based on the peak one-hour measurement since midnight. There is a secondary NAAQS based on a 24-hour average of sulfur dioxide sampled from midnight to midnight, but this NAAQS has such a high starting point that is is never expected to be reached.
The AQI for nitrogen dioxide is based on the peak one-hour measurement since midnight.
The AQI for PM-10 is based on a 24-hour average sampled from midnight to midnight.
The AQI for PM-2.5 is based on a 24-hour average sampled from midnight to midnight.
The AQI for PM-2.5 is based on a 24-hour average sampled from midnight to midnight.

PLEASE NOTE: This data has not been verified by the Clark County Department of Air Quality 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 Clark County Department of Air Quality 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.