Tooele County’s air quality reached an unhealthy level during last week’s inversion.
On Thursday the Utah Department of Air Quality’s air quality monitoring website at air.utah.gov reported that the county’s air quality index reached 106.
The lower limit for the orange level air quality index, or unhealthy for sensitive groups status, is an AQI of 101.
Sensitive groups include people with heart or lung disease, children, older adults, and people who are active outdoors, according to the Utah Department of Health.
During orange level air quality the health department advises people in sensitive groups to reduce prolonged or heavy outdoor exertion. During these days, sensitive people should take more breaks and do less intense activities. They should also watch for symptoms like coughing or shortness of breath.
If ozone levels are high, outdoor activities should be scheduled for the morning or evening when ozone is lower. People with asthma are advised to follow their asthma action plans and keep quick-relief medicine on-hand. For people with heart disease during orange AQI levels, the health department cautions that symptoms like palpitations, chest pain, or unusual fatigue may indicate a serious problem.
Inversions occur during the winter months when normal atmospheric conditions — cool air above, warm air below — become inverted, or turned upside down. Inversions trap a dense layer of cold air under a layer of warm air.
Poor air quality caused by inversions often occurs following snow storms because snow-covered valley floors reflect rather than absorb heat, preventing the normal vertical mixing of warm and cold air that keeps pollutants from building up to unhealthy levels at the surface, according to the Utah Division of Air Quality.
AQI monitors the level of four common pollutants: ground level ozone, particulate matter, carbon monoxide, and sulfur dioxide. An index value is determined for each of these pollutants based on national standards for the pollutant. The highest index is reported as the AQI, according to the U.S. Environmental Protection Agency.
An AQI of 100 or less is generally thought of as satisfactory. An AQI over 100 is considered unhealthy, according to the EPA.
With a range of 1 to 500, the EPA divides the AQI into six categories with color identifiers: 0-50 is good and denoted by green, 51-100 is moderate and yellow, 101 to 150 is unhealthy for sensitive groups and orange, 151-200 is unhealthy and red, 201-300 is very unhealthy and purple, and 301-500 is hazardous and maroon.
So far in 2019 the county has had 252 green days, 50 yellow days and one orange day.
In 2018, Tooele County had 222 green days, 133 yellow days, and 10 orange days, according to the Department of Air Quality.
The most prevalent air pollutant in Tooele County is ground level ozone. It was the highest level of all air pollutants for 266 days in 2018.
Ozone is formed when volatile organic compounds and nitrogen oxides chemically react in the presence of sunlight and heat. Nitrogen oxides and volatile organic compounds are emitted by cars and trucks, industrial facilities, refineries, power plants, household products and cleaning supplies, and paints and solvents.
Wildfires and urban emissions from as far away as Asia contribute to elevated summertime ozone concentrations, according to the EPA.
The second most prevalent air pollutant in Tooele County is a group of particulate matter called PM 2.5, which are fine particles smaller than 2.5 micrometers.
About 30 times smaller than the width of a human hair, PM 2.5 particles can travel deep into the lungs and cause both short-term and long-term health effects.
Most PM 2.5 particles form in the atmosphere as a result of complex reactions of chemicals such as sulfur dioxide and nitrogen oxides, which are pollutants emitted from power plants, industries and automobiles, according to the EPA.
Some PM 2.5 particulate pollution is emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires.
In Tooele County both ozone and PM 2.5 are at their highest during the summer months of June, July and August. PM 2.5 also peaks during the winter months of January and December.
Measured in micrograms per cubic meter, the health standard for PM 2.5 is no greater than 35.5 µg/m³. In 2018, the average daily level of PM 2.5 was 8.07 µg/m³. The standard level was exceeded on four days in Tooele County in 2018.
For ozone, the health standard is no greater than .076 parts per million. In 2018, the average daily level of ozone was .0466. The standard level for ozone was exceeded on two days in 2018 in Tooele County.
The Utah Department of Air Quality reported the source of air pollution in Tooele County during inversions in 2014. DAQ included in its report five primary pollutants: ammonia, nitrogen oxides, PM 2.5, sulfur dioxide, and volatile organic compounds.
The sources were reported in four groups: mobile, point, area and off-road.
Mobile refers to personal and commercial cars and trucks. Point sources include large stationary industrial or commercial sources. Area sources include smaller stationary sources, including small industrial sources, home heating, agriculture, construction, energy production, wildfires and biogenics — emissions from plants and trees. Off-road sources include heavy construction equipment, small engines, trains, and aircraft.
Cars and trucks were the largest source of air pollutants emitted in Tooele County in 2014, accounting for 43.5% of air pollutants.