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Real-Time Smoke
Particulate Sampling
Fire Storm 2000

Regional Air Quality


The smoke from the fires had a severe impact on air quality in the communities across western Montana. Most of the larger communities, including Missoula and Hamilton, have EPA-approved federal reference method (FRM) PM2.5 gravimetric samplers. Several communities also have tapered element oscillating microbalance (TEOM) instruments to provide real-time particulate level information to air-quality specialists. For those communities with a TEOM instrument, air-quality stage alerts were determined using information from that instrument. Other communities used visual techniques to estimate particulate concentrations.

Air Quality Standards

The Clean Air Act, which was last amended in 1990, requires the EPA to set national ambient air quality standards (NAAQS) for pollutants considered harmful to public health and the environment. The Clean Air Act establishes two types of national air quality standards. Primary standards set limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards set limits to protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings. Both PM10 (particulate less than 10 microns in diameter) and PM2.5 are established primary and secondary pollutants.

The limits set by EPA for PM10 are 50 µg/m³ for the annual average and 150 µg/m³ for the 24-h average. Limits set by EPA for criteria pollutant PM2.5 are 15 µg/m³ for the annual average and 65 µg/m³ for the 24-h average.

The EPA developed an air quality index (AQI) to provide a consistent and easy way to understand air pollutant concentrations and their health implications. The EPA AQI values are based on PM2.5 for the 24-h average. To help communities further understand the air quality issues associated with forest fire smoke, the Montana State Department of Environmental Quality (MT DEQ) established AQIs for 8-h and 1-h average concentrations. Table 1 shows the values and associated health risks for all three AQIs.

Table 1—Air quality index (AQI) as established by the U.S. Environmental Protection Agency and the Montana Department of Environmental Quality. Values are for 1-, 8-, and 24-h averages.

Categories
Health effects
Cautionary statements
EPA 24h AQI (µg/m3)
MT DEQ 8h AQI (µg/m3)
MTDEQ 1h AQI (µg/m3)
Good None None
0–15
0–22
0–38
Moderate Possibility of aggravation of heart or lung disease among persons with cardiopulmonary disease and in the elderly. None
15–40
22–58
38–101
Unhealthy for sensitive groups Increased likelihood of respiratory symptoms in sensitive individuals. Aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and in the elderly. People with respiratory or heart disease, the elderly, and children should limit prolonged exertion.
40–65
58–93
101–164
Unhealthy Increased aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and in the elderly; increased respiratory effects in the general population. People with respiratory or heart disease, the elderly, and children should avoid prolonged exertion; everyone else should limit prolonged exertion.
65–150
93–215
164–376
Very unhealthy Significant aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly; significant risk of respiratory effects in the general population. People with respiratory or heart disease, the elderly, and children should avoid any outdoor activity; everyone else should avoid prolonged exertion.
150–250
215–358
376–626
Hazardous Serious aggravation of heart or lung disease premature mortality in persons with cardiopulmonary disease and in the elderly; serious risk of respiratory effects in the general population. Everyone should avoid and any outdoor exertion; people with respiratory or heart disease, the elderly, and children should remain indoors.
250 +
358 +
626 +

The MT DEQ also established visibility ranges (table 2) to help communities without real-time monitoring equipment estimate particulate concentrations. The MT DEQ established these visibility ranges using empirical data collected from the Automated Surface Observing System visibility sensor located at the Helena airport and particulate concentrations collected nearby.

Montana Department of Environmental Quality (DEQ) visibility categories
Category
Visibility (miles)
Good
> = 11.6
Moderate
4.45–11.5
Unhealthy for sensitive groups
2.75–4.44
Unhealthy
1.2–2.74
Very unhealthy
0.7–1.1
Hazardous
< 0.7

Missoula and Hamilton Air Quality

The real-time instruments deployed by MTDC for this evaluation were operated almost continuously from about August 10 through the end of the month. Data from the real-time instruments were corrected using empirical formulas developed as a result of the evaluation. The following summary of the air quality in Missoula and Hamilton is based on the results from the real-time instruments' corrected data.

In Hamilton, the 1-h running average peak for PM2.5 reached as high as 500 µg/m³ and the running 24-h average reached as high as 284 µg/m³ (figure 4 and figure 5). The 24-h PM2.5 average reached the hazardous level as described by the EPA and MT DEQ AQI. Missoula reached running 1-h average peaks of 400 µg/m³ and 24-h average peaks of 204 µg/m³ for PM2.5.

Chart showing the mass concentrations of Missoula and Hamilton throughout the month of August 2000.
Figure 4—The estimated 1-h running mass concentration
averages for PM2.5 in Missoula and Hamilton, MT, during August 2000.
Results are from the corrected values of the MIE DataRam real-time
particulate monitor. Hazard category levels for forest fire smoke were
determined by the Montana Department of Environmental Quality.

-Continued-

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