Clark County's First 2021 Ozone Exceedance Registered May 14

Clark County's First 2021 Ozone Exceedance Registered May 14

Media Contact:
Kevin J MacDonald, Public Information Administrator
702-232-0931 (mobile)

Tuesday, May 18, 2021

Clark County's First 2021 Ozone Exceedance Registered May 14
Indian Springs monitoring station is only station in Clark County to record exceedance.


Clark County’s Department of Environment and Sustainability registered the region’s first ground-level ozone exceedance of 2021 on Friday, May 14. According to air quality specialists with the department’s Division of Air Quality, its monitoring station located in Indian Springs registered an Air Quality Index (AQI) of 108, eight points higher than allowed by the U.S. EPA’s National Ambient Air Quality Standards (NAAQS). None of the other 11 DES monitoring stations throughout Clark County registered an exceedance.

According to Air Quality Specialist Paul Fransioli, wildfire smoke in addition to ozone-producing pollutants transporting from southern California may have contributed.

“Our preliminary analysis of airflow source regions show possible influence of the Pine and Palisades fires burning north and west of the Los Angeles basin,” said Fransioli. “The ozone AQI was more than 20 points higher on May 14 than the few days before and after the exceedance.”

While ozone exceeded the NAAQS at the Indian Springs monitoring site, four additional monitoring stations also registered high concentrations of ozone on May 14.

“Ozone AQI levels reached 100 at four sites in the greater Las Vegas valley, barely missing the exceedance level” said Fransioli.”

What Causes Ozone?
Ground-level ozone is formed when volatile organic compounds (VOCs) mix with oxides of nitrogen (NOx) in ultraviolet rays and heat. VOCs include fumes from fuel, paints and chemicals, and even some plants and vegetation. Examples of NOx are vehicle exhaust, factory emissions and wildfire smoke. Stagnant weather conditions and the topographic structure of the Las Vegas Valley help trap these pollutants, causing levels to rise. Exposure to ozone can irritate your respiratory system and cause coughing, a sore throat, chest pain and shortness of breath even in healthy people, according to the EPA.

What is an Exceedance?
According to the EPA, an exceedance for ground-level ozone occurs when ozone concentrations are greater than 70 parts per billion (ppb) over the course of eight rolling hours per 24 hours in a day. As concentrations of ground-level ozone increase, so increases the Air Quality Index.

Air Quality Index
Used by the EPA to measure and report air quality, the Air Quality Index (AQI) serves as a color-coded “yardstick” that runs from 0 – 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. Six pollutants are measured using the AQI: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter and sulfur dioxide.


About the Department of Environment and Sustainability
The Department of Environment and Sustainability is the air pollution control agency, regional Endangered Species Act compliance program, and sustainability office for all of Clark County, Nevada. Established as the Department of Air Quality by the Clark County Commission in 2001, it was renamed in 2020 and is comprised of three divisions: Air Quality, Desert Conservation Program and Office of Sustainability. Through these three divisions, DES is ensuring the air we share meets healthful, regulatory standards, administering the County's Multiple Species Habitat Conservation Plan and addressing climate change.


Clark County is a dynamic and innovative organization dedicated to providing top-quality service with integrity, respect and accountability.  With jurisdiction over the world-famous Las Vegas Strip and covering an area the size of New Jersey, Clark is the nation’s 11th-largest county and provides extensive regional services to 2.4 million citizens and 45.6 million visitors a year (2019). Included are the nation’s 9th-busiest airport, air quality compliance, social services and the state’s largest public hospital, University Medical Center. The County also provides municipal services that are traditionally provided by cities to 1.1 million residents in the unincorporated area. Those include fire protection, roads and other public works, parks and recreation, and planning and development.


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