Prescribed burning is the intentional burning of a specific plot of land for the purposes of managing or restoring vegetation. The use of prescribed fires appears to be increasing throughout the Midwest and within Nebraska. Although prescribed fires do not completely duplicate natural wildfires, they do accomplish many of the same results:
- destruction of invasive species such as red cedar and locust trees,
- increasing species diversity with respect to native long- and mixed-grass prairie species, and
- release of nutrients back into the soil to promote growth of prairie grasses and forbs.
The map below shows the original range of prairies in the central plains, including the Flint Hills region in Kansas. The remaining tallgrass prairies in the Flint Hills comprise approximately 4% of the 170 million acres once covered by tallgrass prairie. It is in this region where concentrated annual prescribed burning occurs.
Smoke and Health
The smoke created by prescribed fires can present public health concerns. Smoke contains air pollutants that can be harmful when inhaled, and can be transported long distances, covering large areas of the continent, before dissipating. Smoke transport is dependent on numerous factors such as temperature, humidity, and wind conditions.
The pollutant most often associated with smoke impacts is fine particulate matter, or PM2.5. These particles have a diameter of 2.5 microns or less – smaller than that of a human hair – and can be inhaled deep into the lungs.
There are many ways to measure and describe ambient air quality. A description of two of the most common methods follow. It is important to recognize the different methods are developed for different reasons. The first method was developed to determine compliance with health-based standards on a daily and annual basis. The second method is more of an immediate indicator of air quality and includes actions that people can take if air quality is compromised.
National Ambient Air Quality Standards
First, the Environmental Protection Agency (EPA) has established health-based National Ambient Air Quality Standards (NAAQS) for PM2.5 as noted below:
|Daily NAAQS || 35 ug/m3 (based on a 24-hour average)|
|Annual NAAQS ||12 ug/m3 (based on a year-long average)|
(ug = Micrograms)
Compliance with these standards is evaluated by analyzing air monitoring data over a three-year period. For annual NAAQS, a simple three-year average is used; for the daily 24-hour NAAQS, a more complicated statistical calculation is used (i.e., the three-year average of the 98th percentile values, where the 98th percentile value is the annual 8th highest value when monitoring daily).
Nebraska has five ambient air monitors that measure PM2.5 concentrations in or near areas of the highest predicted concentrations (Omaha, Lincoln, South Sioux City, Grand Island, and Scottsbluff). Data from these monitors indicate that Nebraska is in compliance with the NAAQS, but also that there are instances when daily PM2.5 concentrations exceed the NAAQS. (The daily PM2.5 NAAQS allows for 7 exceedances per year as described above i.e., the 24-hour average uses the 8th highest value.)
Air Quality Index
EPA has developed the Air Quality Index (AQI) to provide the public a simple matrix for evaluating the health impacts and adverse effects of air pollution. AQI levels and recommended actions are shown in the table on the following page.
Source: https://www.airnow.gov/index.cfm?action=pubs.aqguidepart *
Air Quality Index
Who Needs to be Concerned?
What Should I Do?
It’s a great day to be active outside.
Some people who may be unusually sensitive to particle pollution.
Unusually sensitive people: Consider reducing prolonged or heavy exertion. Watch for symptoms such as coughing or shortness of breath. These are signs to take it easier.
Everyone else: It’s a good day to be active outside.
Unhealthy for Sensitive Groups
Sensitive groups include people with heart or lung disease, older adults, children and teenagers.
Sensitive groups: Reduce prolonged or heavy exertion. It’s OK to be active outside, but take more breaks and do less intense activities. Watch for symptoms such as coughing or shortness of breath.
People with asthma should follow their asthma action plans and keep quick relief medicine handy.
If you have heart disease: Symptoms such as palpitations, shortness of breath, or unusual fatigue may indicate a serious problem. If you have any of these, contact your health care provider.
151 to 200
Sensitive groups: Avoid prolonged or heavy exertion. Move activities indoors or reschedule to a time when the air quality is better.
Everyone else: Reduce prolonged or heavy exertion. Take more breaks during all outdoor activities.
Sensitive groups: Avoid all physical activity outdoors. Move activities indoors or reschedule to a time when air quality is better.
Everyone else: Avoid prolonged or heavy exertion. Consider moving activities indoors or rescheduling to a time when air quality is better.
Everyone: Avoid all physical activity outdoors.
Sensitive groups: Remain indoors and keep activity levels low. Follow tips for keeping particle levels low indoors.
What Does the AQI Level Mean in terms of the PM2.5 Concentration?
The PM2.5 AQI levels (24-hour) correspond to pollutant concentrations as follows:
Source: https://aqs.epa.gov/aqsweb/documents/codetables/aqi_breakpoints.html *** Values in the ‘Good’ and ‘Moderate’ category correspond to concentrations that are within the 24-hour NAAQS for PM2.5.
PM2.5 Concentration Level
less than 12 ug/m³
12-35 ug/m³ **
Unhealthy for Sensitive
greater than 250 ug/m³
Over the past five years, Nebraska has experienced fewer than five exceedances per year of the NAAQS for PM2.5. Because the 8th highest value is used when determining compliance, there have been no regulatory violations of the standard. However, when a short-duration exceedance occurs, it can and does have public health impacts as indicated in the AQI table above. Because the source of the smoke is predominantly from outside Nebraska and the frequency of these episodes has not resulted in violation of the NAAQS, Nebraska currently has no regulatory recourse to address these exceedances.
The 2018 Prescribed Burn Season
It is likely that Nebraska air quality will be impacted by wildfires and/or prescribed fires in 2018. Extensive use of prescribed fires in the Flint Hills has impacted southeast Nebraska in the past. Moreover, increased use of prescribed burning in Kansas and Nebraska outside the Flint Hills region can impact air quality in the state as well. These smoke impacts on southeast Nebraska have occurred most often during the month of April, although wildfire smoke can occur almost any time of year.
How can I evaluate the impact of smoke in the air?
- The AQI provides a tool for evaluating public health impacts, particularly important to those in sensitive groups. The AQI (current conditions and forecast) are available on EPA’s AirNow website (www.airnow.gov). However, data from past smoke incidents indicate that the AirNow forecasts lack some accuracy in relating current air quality conditions to the 24-hour average conditions.
- Local health agencies and the NDEQ may also provide air quality/AQI updates on their websites.
- Use your senses. Is the air hazy? Does it smell smoky? Elevated concentrations of PM2.5 produce a visible haze that may indicate smoke impact before you smell the odor of smoke.
- Many of the past incidents of significant smoke impacts have followed a similar pattern: smoke accumulates in the late afternoon or evening hours, is most noticeable in the early morning hours, and then dissipates in mid-late morning as temperatures increase. Plan activities accordingly to avoid periods of highest PM2.5 and smoke impacts using the table above a guide.
While burning in the Flint Hills is often referred to as adversely impacting air quality in southeast Nebraska, it is important to recognize that in years past wildfires from as far away as northern Canada and Oregon and Washington have also had adverse impacts.
Regardless of where the fires originate, the Dept. of Environmental Quality is committed to working with Kansas and other sources of smoke to minimize and, if possible, eliminate adverse impacts. NDEQ welcomes comments, suggestions and questions regarding air quality issues. For more information, contact NDEQ at (402) 471-2186, or toll free at 1-877-253-2603; e-mail – firstname.lastname@example.org.
* This document contains links to non-NDEQ websites; these links will open in a new tab or window.