United States

Department of 

Agriculture

Forest Service

Pacific Northwest

Research Station

General Technical

Report

PNW-GTR-251

March 1990

Airborne Monitoring and Smoke

Characterization of Prescribed

Fires on Forest Lands in

Western Washington and Oregon:

Final Report

Lawrence F. Radke, Jamie H. Lyons, Peter V. Hobbs, Dean A. Hegg,

David V. Sandberg, and Darold E. Ward

About This File: 

This file was created by scanning the printed publication. Misscans identified

by the software have been corrected; however, some mistakes may remain.
LAWRENCE F. RADKE is research professor, JAMlE H. LYONS is meteorologist,

PETER V. HOBBS is professor, and DEAN A. HEGG is research associate 

professor, University of Washington, Department of Atmospheric Sciences,

Seattle, WA 98195; DAVlD V. SANDBERG is supervisory research forester,

Pacific Northwest Research Station, Forestry Sciences Laboratory, 4043

Roosevelt Way, NE, Seattle, WA 98105; and DAROLD E. WARD is supervisory

research chemist, lntermountain Research Station, lntermountain Fire Science

Laboratory, P.O.Box 8089, Missoula, MT 59807.

The material was prepared for Lockheed Engineering and Management Services

Company, Inc., Las Vegas, NV 89114, under EPA contract no. 68-03-3050, U.S.

Environmental Protection Agency, Office of Research and Development,

Environmental Monitoring Systems Laboratory, Las Vegas, NV 89114. This 

report supersedes two previous drafts.

Authors
Radke, Lawrence F.; Lyons, Jamie H.; Hobbs, Peter V.; Hegg, 

Dean A.; Sandberg, David V.; Ward, Darold E. 1990. Airborne 

monitoring and smoke characterization of prescribed fires on forest lands in 

western Washington and Oregon. Gen. Tech. Rep. PNW-GTR-251. Portland, 

OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest 

Research Station. 81 p.

Detailed airborne measurements of smoke plumes from seven prescribed burns 

of forest biomass residues leftover from timber harvests in Washington and 

Oregon are described. Measurements of particle size distributions in the plumes 

at ≈3.3 km downwind of the burns showed a prominent peak in the mass concentration for particles ≈0.25-0.30 μm in diameter. The total mass of particles in the

plume was dominated, however, by supermicron-sized particles. The particle 

number distributions were dominated by large numbers of Aitken nuclei (median

number diameter ≈0.15 μm).

Based on numerous airborne measurements from six burns, the following 

average emission factors were determined using the carbon balance method: for

total suspended particulates 1.2±0.4 percent, for particles <43 μm in diameter

0.6±0.3 percent, and for particles <0.2 μm in diameter 0.4±0.2 percent. Particle

mass fluxes for total suspended particulates, particles <43 μm diameter, and 

particles <2 μm diameter ranged from 0.1 to 2.4 kg•s-1, 0.1 to 1.1 kg•s-1, and 0.1 

to 0.8 kg•s-1, respectively, for the smaller Oregon burns and from 1.1 to 11.7 

kg•s-1, 0.6 to 7.0 kg•s-1, and 0.4 to 14.1 kg•s-1, respectively, for the larger

Washington burns.

Other samples collected in conjunction with the airborne work included those for

trace gas analysis, particulate matter for trace element analysis, and gas 

concentration measurements for carbon-mass analysis (oxides of nitrogen, 

ozone, and hydrocarbons). Mass concentration-to-light scattering coefficient 

algorithms and ratios, which can be used to convert integrating nephelometer

response to mass concentration units, are also reported.

Keywords: Emissions, prescribed burning, smoke management.

Abstract
1 lntroduction

2 2. Aircraft lnstrumentation System 

2 2.1 Overview

2 2.2 Particle Measuring System 

6 2.3 Trace Gas Measuring System 

6 2.4 General Meteorological lnstrumentation 

6 2.5 Data Processing System

9 3. Summary of Research Flights

9 4. lnstrument Calibration and Data Quality Control 

9 4.1 lnterim Calibration Performed In-House

10 4.2 RTI Field Audit

11 4.3 Comparison of Plume Minus Ambient CO2 Concentrations 

12 5. Flight Procedures and Data Processing 

12 5.1 Flight Procedures 

12 5.2 Data Processing 

14 5.3 Physical lnterpretation of bscat Algorithms 

17 6. Preliminary Results and Analysis 

17 6.1 Characterization of Cross Sections of the Plumes 

23 6.2 Some Characteristics of the Particles in the Plumes 

35 6.3 Analysis and Cross Comparisons of Bulk Air Samples 

36 6.4 Plume Tracers 

37 6.5 Particle Emission Factors 

42 6.6 Particle Mass Fluxes 

44 7. Topics for Further Study

44 8. Conclusions

45 English Equivalents 

46 Literature Cited 

48 Appendix A

53 Appendix B 

59 Abbreviations

60 Tables 1-14

Contents
Forest fires, prescribed burning of forest logging wastes, and agricultural burning

create a portion of the particles injected directly into the atmosphere (SCEP

1970). Ward and others (1976) noted that about 107 ha of forest land are burned

annually in the United States and that estimates of the quantity of particles emitted into the atmosphere from this source range from 0.5 to 50 million metric tons

per year. The Environmental Protection Agency (EPA) has estimated the total 

direct emission of particulate matter from all sources in the United States to be 20

million metric tons per year (SCEP 1970). The upper limit for estimates of 

particles from the burns of forest land clearly is inconsistent with the EPA estimate

for total emissions. The uncertainties are due to the limited data base and also to

the difficulty in obtaining good measurements of particle emission rates from large

areal sources such as forest fires.

This paper reports on part of a larger study to characterize particle emissions from

the prescribed burning of forest biomass (residues from harvesting) as functions 

of time, combustion character, fuels, and forestry practices. Measurements were

made of the plumes from seven prescribed burns conducted during 1982 in

Washington and Oregon. Five of the tests were designed to increase knowledge 

of the effects of residue removal—to various size specifications—on emissions (one

of the problem areas being studied by the USDA Forest Service, Pacific Northwest

Research Station, Forest Residues and Energy Program). The other two tests 

were conducted to examine mass-ignition techniques (such as heliotorch) as 

emission-reduction methods. It was hypothesized that rapid ignition may be one

way to reduce the composite emissions factor and to limit the period of smoldering

combustion. The combined data set supplements work completed during 1981, 

in which two prescribed fires were sampled (Anderson and others 1982, Sandberg and Ward 1982, Ward and Sandberg 1982).

This report deals only with the airborne measurements of the emissions from the

seven prescribed burns as obtained by the Cloud and Aerosol Research Group at

the University of Washington (UW). Some preliminary analyses are also presented of samples collected by UW but analyzed by Lockheed Engineering and

Management Services Company (LEMSCO), the Oregon Graduate Center 

(OGC), and the Crocker Laboratory, at the University of California at Davis. We will

characterize the fires as to plume dimensions, particle size distributions, particle

densities, and particle emission fluxes. This report was prepared without detailed

information on ignition techniques, "yarding" preparation, fuel moisture, and 

other surface measurements related to the prescribed burns so that our analysis 

of the emissions could be as independent as possible.

Besides the emissions characterizations that are discussed, several other types 

of data were collected by cooperators working under the leadership of the U.S.

Department of Agriculture (USDA) Forest Service, Pacific Northwest Research

Station. The data collection, data reduction, and analysis were coordinated by 

the USDA Forest Service, (see Ward and Sandberg 1982). The study was 

cooperatively funded and administered by the USDA Forest Service PNW 

Research Station; EPA Region X; the U.S. Department of Energy, Region X,

1

1. Introduction
through the Bonneville Power Administration; and the EPA Environmental

Monitoring Systems Laboratory.

The aircraft used in this study was a Douglas B-231 which is maintained and 

operated by the Cloud and Aerosol Research Group of the Atmospheric 

Sciences Department at UW, Seattle.

The trace gas and aerosol instrumentation aboard the aircraft is shown in figure 1,

and descriptions of the instruments are given in table 1. The measurements of 

interest in this study included descriptions of particle size distributions and the

masses of suspended particulates. The masses of suspended particulates were

measured by weighing filters exposed to the air and by a microbalance cascade

impactor (with a diffusion dryer) and-a mass monitor (with a 2- μm diameter cutoff

inlet impactor and diffusion dryer). The overall performance of the complete 

measuring system was excellent during the several experiments.

The particle light-scattering coefficient of air was measured with an in-house 

modified, MRI 1567 integrating nephelometer, which sampled from a 30-L

plenum chamber maintained at 5 °C above ambient temperatures. Outside 

ambient air was brought into this chamber isokinetically by means of a pump 

connected to a static pressure transducer that maintained zero overpressure 

in the head and line of the sample probe to the plenum chamber. The aboveambient temperature of the plenum chamber ensured that only dry particles 

entered the integrating nephelometer.2

The main filter sampling system consisted of a ≈500-L polyethylene bag, which 

was filled nearly isokinetically by ram air through a 6.3cm diameter sample port,

a filter sampling manifold with flowmeter, and an engine-driven vacuum pump. The

bag took ≈5 seconds to fill and entrained all particles <5 μm in diameter (the collection efficiency of the system for particles >5 μm was not quantified). After the bag

was filled, a sample of the air in the bag was pulled through a Teflon filter 

37 mm in diameter. Sample flow rates and mass flow volumes were measured by 

a TSI 2013B mass flow sensor interfaced with a microprocessor. Postflight 

analysis of the filters was done at the Crocker Laboratory. The results of these

analyses will be discussed.

1 Use of a trade name does not imply endorsement or approval of 

any product by the USDA Forest Service to the exclusion of 

others that may be suitable.

2 Air from the plenum chamber was automatically passed 

through a set of filters when the light-scattering coefficient 

indicated that the aircraft was in the plume from a burn. 

These filters were sent for analysis to the Crocker Laboratory, 

University of California at Davis.

2

2. Aircraft 

lnstrumentation

System

2.1 Overview

2.2 Particle Measuring

System
3

Figure 1—Aerosol and trace gas instrumentation aboard the 

University of Washington's B-23 research aircraft. Meteorological, 

navigational, cloud, and precipitation instrumentation are not 

shown.

A major subunit of the UW particle-measurement system measures size spectra of

the atmospheric aerosol. Because the particles spanned a size range on a logarithmic scale of nearly four decades in diameter, several different sensors had to be

used. This is illustrated in figure 2 where a typical volume distribution for a power

plant plume is shown with the various instruments used to measure the sizes of 

the particles in the distribution.
Figure 2—Diameter (D) ranges of the particle sizing instruments 

aboard the University of Washington's B-23 aircraft shown with 

respect to the volume (V) distribution of particles in a power plant: 

DB-ANC = diffusion battery coupled to an Aitken nucleus counter; 

EAA = electrical aerosol analyzer; ASAS = active scattering laser 

probe; LAS-200 = laser aerosol spectrometer; Royco 245 = 

forward light-scattering optical device; and MCI = microbalance 

cascade impactor.

These instruments have widely differing response and analysis times. This variability requires that all instruments sample from a common batch sample of air to

obtain comparable measurements. A batch sample is also necessary if sharp

concentration gradients of particles exist in the air, such as the smoke plumes

described here. The batch sampler used on the B-23 consisted of a ≈90-L cylinder (≈150 cm high) with a freely floating piston to cap the sample. Air pressure forces the piston up, which fills the cylinder with ambient air. Because the

sample offers negligible resistance to the incoming air, sampling is essentially

isokinetic. After the cylinder is filled, the various particle-sizing instruments 

sample from the base of the cylinder (to avoid loss or sedimentation). A

schematic of this batch sampler is shown in figure 3.

4
Figure 3—The batch air sampler aboard the University of 

Washington B-23 aircraft.

The smallest particles measured are sized by an electrical aerosol analyzer (EAA)

and a diffusion battery coupled to an Aitken nucleus counter. The EAA operation 

is based on the relations among the charge, size, and electrical mobility of a 

particle. Particles entering the instrument are charged, their mobilities in an 

electrical field are measured, and their sizes are deduced. The diffusion battery

measures particle sizes by determining the number of fine-mesh screens the 

particles can pass through. The greater the screen "penetration," the larger the

size of the particles. Particle detection is achieved with an Aitken nucleus count

er. In this study, the EAA generally functioned well; therefore, the diffusion 

battery data, which require extensive computer processing, were not analyzed.

Particles of intermediate size (see fig. 2) were measured with a particle-measuring

system (PMS) active scattering laser probe (ASAS). This device is essentially an

open-cavity laser; the measuring principle is based on the fact that a particle passing through the pumping cavity of a laser will "detune" the laser to an extent 

proportional to the size of the particle. Medium- to large-sized particles are measured with a PMS laser aerosol spectrometer (LAS-200) and a forward light scattering spectrometer (Royco 245). The LAS-200 determines particle sizes by 

measuring the quantity of light scattered in the forward direction with a laser, and

the Royco 245 does so with filament light source.

5
A microbalance cascade impactor (MCO, supplied by EPA, was fitted with a diffusion

dryer and placed near the inlet port of the large diffusion dryer. The total length of

plumbing from the MCI to the batch sampler port was about 30 cm with a residence

time of less than 1 second. The MCI had 10 stages, between 0.05 and 24 μm; 

however, because of the sampling inlet, only a small fraction of the aerosol <10 μm

should have reached the MCI. The MCI was easily overloaded with aerosol, and it

was not practical to clean it in flight. The number of samples taken with the MCI

therefore was deliberately restricted.

Trace gas analyzers aboard the B-23 provided continuous measurements of the 

concentrations of SO2, O3, and NOx in the atmosphere. Excess ethylene was 

supplied to a reaction chamber through which ambient air was drawn, and the O3

instrument measured ozone by monitoring the chemiluminescence from the 

ozone-ethylene reaction.

The NO/NO2 monitor is a dual-reaction chamber device; in one chamber, measurements are made of the chemiluminescence of the NO+O3 reaction by supplying

excess O3 to ambient air drawn into the chamber. In the other chamber, excess O3

iS Supplied to the ambient air that has passed over a catalytic-reducing agent to

reduce to NO any NO2 present. The difference between the NO concentrations

measured in the two chambers is attributable to NO2.

The regular sampling system for halocarbons and hydrocarbons aboard the B-23 

aircraft consisted of one stainless steel sample loop 1.3 cm in diameter and about 

25 m long that air was pumped through into a stainless steel canister with electropolished interiors. An overpressure of roughly 1 atmosphere was pumped into 

each canister. Some canisters filled through this system were supplied to the 

OGC for analysis. Because we required most of the canister samples to be coincident with the filter samples, the canisters were generally filled from the 

500-L polyethylene bag (rather than from the stainless steel system). These 

samples were analyzed after each flight by LEMSCO by using gas-chromatography coupled with appropriate detectors. Use of the polyethylene bag 

compromised the measurements of some trace constituents (see section 4.3).

Measurements of the concentrations of CO2 in the air (in real time) were made 

with a Miran/Foxboro long-path IR sensor. Carbon monoxide (CO) measurements

were made with an Ecolyzer electrochemical oxidation instrument.

The general meteorological instrumentation aboard the B-23 for measuring 

temperature, humidity, horizontal and vertical winds, and ultraviolet light intensity 

is listed in table 1. It is all standard equipment.

Data flow charts are shown in figures 4, 5, and 6. In-flight comments by the pilots

and crew were recorded on the aircraft instrumentation tape (fig. 4). Later, these

were reproduced for transcript typing. High-resolution data and computer serial

6

2.3 Trace Gas Measuring

System

2.4 General Meteorological

lnstrumentation

2.5 Data Processing

System
7

Figure 4—Flow chart for aircraft instrumentation tape to seventrack computer tape and voice transcripts.

digital products (backup to disk data) were frequency-shift-keyed, demodulated,

and processed into appropriate engineering units on a Raytheon 704 minicomputer (fig. 4). The seven-track computer tape from the Raytheon can be 

directly reprocessed into printouts or strip charts of the high-resolution data or

transferred, via a PRlME 400 minicomputer, to nine-track tapes for further 

processing (fig. 5).
8

Figure 6—Flow chart for processing nine-track tapes into final 

hard copy printouts and graphics.

Figure 5—Flow chart for conversion of seven-track computer 

tapes and floppy disks to nine-track tapes and preliminary 

analysis hard copies.
The serial digital stream from the aircraft computer normally was not recovered

from the instrumentation tape but was taken directly from floppy disks (fig. 5) and

converted to nine-track tape via a Computer Automation's A-LS1-2 minicomputer.

Major computational efforts and graphics products were handled on the A-LSI-2

computer from a nine-track tape (fig. 6). This is a well-proven system that provides

both flexibility and redundancy in data recording and processing.

On July 2, 1982, a preliminary quality control check was made of the instrumentation aboard the B-23 aircraft. The period between July 22 and July 27, 1982 

was spent in Eugene, Oregon, to make four research flights through smoke 

plumes over the area of prescribed burning of timber harvest residues (broadcast

slash burning) on units harvested to different size specifications in the Willamette

National Forest (Joule Sale area). During this period, a second quality control

check was completed on the airborne instrumentation system. Two research 

flights were made during September 1982 over two prescribed burns in the Twin

Harbors area of Washington State. Table 2 summarizes the research flights made

in support of this project.

The interim calibration was performed in-house on June 29, 1982.

Ozone—The ozone analyzer was calibrated against a Monitor Labs 8510 Permacal O3 source (UV irradiation), which was calibrated against neutral-buffered potassium iodide. Eight points were used in the calibration. The data produced the 

following calibration equation:

PO3 (real) = 1.08 PO3 (indicated) - 1.46 ppb ;

where PO3 (real) and PO3 (indicated) are, respectively, the actual concentrations

of ozone and the concentrations as indicated by the instrument in parts per million. The correlation coefficient for the calibration equation was 0.998.

Nitrogen oxides—The NOx analyzer (both channels) was calibrated against a

Monitor Labs Permacal calibration source (permeation tube and span gas dilution), which was calibrated against gas-phase titration. Four points per channel

were used in the calibration. The resulting calibration equation was:

PNO x (real) = 1.65 PNOx (indicated) - 7.876 ppb ;

where the concentrations are in parts per billion. The correlation coefficient in this

case was 0.97.

Carbon dioxide—The carbon dioxide analyzer was calibrated against an inhouse dynamic dilution system employing concentrated CO2 and ultrapure NP2

Although seven calibration points were employed, the inherent nonlinearity of 

the instrument rendered a single linear calibration over the entire range of

9

3. Summary 

of Research 

Flights

4. Instrument

Calibration 

and Data Quality

Control

4.1 lnterim Calibration

Performed In-House
calibration (0-4000 ppm) impractical. For example, the calibration equation for the

entire range (based on linear regression) was:

PCO2 = 7.395 x 103 (absorption) - 323.6 ppm ;

with a linear regression coefficient of 0.937. This equation predicts values of

PCO2 as much as 68 percent too high at lower PCO2 (relative to the actual 

calibration values). If the linear regression is applied only up to 1000 ppm (a value

still much in excess of any CO2 measured during the study) the calibration 

equation becomes:

PCO2 = 3.6514 x 103 (absorption) - 7.939 ppm ;

with a correlation coefficient of 0.99. This equation predicts PCO2 to within 16 

percent of the actual calibration values and was used in the data reduction for this

project.

Carbon monoxide—No attempt was made to calibrate the carbon monoxide 

analyzer before the audit by the Research Triangle lnstitute (RTD. The RTI audit

therefore constitutes the calibration. This instrument suffers from excessive zero

drift and must be constantly rezeroed to obtain accurate readings.

lntegrating nephelometer—The integrating nephelometer was calibrated by

comparing the instrument output when viewing clear air and Freon 12 with the

expected bscat (light-scattering coefficient) values for these substances. The 

following results were obtained:

Clean air Freon 12 

Observed (1.8±1.0)•10-5•m-1 3.4•10-4•m-1

Expected 1.5•10-5•m-1 2.4•-4•m-1

The differences between the observed and expected values were used to adjust

the data collected in this field project.

The results of the second audit of the instrumentation used aboard the B-23 and

by LEMSCO are summarized in table 3.3 The audit was made at Mahlon Sweet

Airport, Eugene, Oregon, July 26-27, 1982.

3 Data taken from: Murdock, R.W. [1982]. Second audit of 

airborne monitoring prescribed fires in the Willamette National 

Forest. RTI Report No. RTI/NIX 26/00-02F. No unresolved 

differences were noted between first and second audit.

10

4.2 RTI Field Audit
Airborne instrumentation—The ambient air quality analyzers aboard the B-23 

were audited for measurements of the concentrations of CO2, CO, NOx, and O3.

The measurements of CO2, CO, and the total NOx were satisfactory. The ozone

analyzer read systematically 15 percent higher than the RTI standard with excellent

traceability (correlation coefficient 0.9999). If the RTI standard is accepted, then 

the ozone concentrations reported hereafter should be reduced by 15 percent. 

The audit showed the flow rates on the quartz crystal microbalance and the Ghia 

filter sampler to be satisfactory. The Rosemount temperature sensor, Cambridge

lnstruments dew point sensor, and the integrating nephelometer aboard the B-23

exhibited satisfactory performance.

The problem with the nitrogen oxides analyzer was not resolved; we accepted 

the analysis by RTI that the converter (NO to NO2) did not function linearly, which

resulted in NO2 measurements that were systematically low relative to the calibration values. The error would be of order 10 percent for concentrations of NO2 in 

the sub-part-per-million range. The measurements of NOx were, however, in 

excellent agreement with the calibration. These problems have no impact on the

data presented in this report.

LEMSCO Instrumentation—The Byron Model 401 gas chromatograph operated by LEMSCO was audited for measurements of the concentrations of carbon

monoxide, carbon dioxide, methane, total hydrocarbons, and non-methane hydrocarbons. The carbon dioxide channel gave excellent performance; and the

methane, total hydrocarbon, and carbon monoxide channels gave satisfactory 

performance. The nonmethane hydrocarbon channel was unsatisfactory (based 

on the intercept of the linear regression equation).

The data available for the comparison of the CO2 measurements as made by OGC

and LEMSCO from air samples collected in the stainless steel canisters via the 

polyethylene bag are shown in table 4. Each of the canister samples listed was 

analyzed by both systems with the indicated results. These results suggested an

analytical discrepancy of about +20 percent.

Two samples were available to compare the polyethylene bag sampling system

(employed most of the time) with the stainless steel sample loop system (used for

some of the OGC samples). The results of these comparisons are shown in table 

5. They suggest an additional discrepancy, this time systematic, of ≈20-60 percent, with the LEMSCO concentrations greater than those of OGC. This might be 

a bag-contamination problem, although it is unclear how such a large discrepancy

could arise. The quantity of data is insufficient to warrant further discussion.

11

4.3 Comparison of Plume

Minus Ambient CO2

Concentrations
Each plume was studied by flying the UW B-23 aircraft at various altitudes across

the width of the plume, generally at a range of 3.3 km (2 nautical miles) from the

burn. The range was initially determined by use of visual terrain references and

quadrangle maps. In cases where the plume fanned, or ground references 

became obscured, the range from the burn was computed in real time using data;

from the doppler radar aboard the aircraft. Our position repeatability appeared, 

overall, to be excellent.

The traverses of the plume at various altitudes at a given distance downwind of a 

burn were labeled A, B, C, D, and E; where A, C, and E were the top, center, and

bottom penetrations, respectively. The top and bottom penetrations were chosen visually such that ≈10 percent of the vertical dimension of the plume was 

above A and below E. The center of the plume was estimated visually, but it was

generally about halfway between A and E. If the plume had sufficient vertical 

extent to sample at five levels, the B and D samples were taken midway between

A and C and between C and E, respectively. When the plume lacked sufficient 

vertical depth for five traverses, the B and D samples were omitted.

Each cross section of the plumes presented in this report consisted of at least 

the A, C, and E traverses. The next cross section (in time sequence) at the same

range used the previous traverse (either A or E) as the first traverse of the new

cross section. It is assumed that the burns were of sufficiently steady states so 

that each cross section can be considered as if each of the plume traverses that

comprise it were made simultaneously. The bag and batch samples were obtained as close as possible to the center of the plume. Because they were taken 

over a path with a minimum length of 300 m and required some degree of anticipation, they can be considered as located randomly about the central region of 

the plume. Because each filter required at least two bag samples, at least two 

traverses of the plume were made at each altitude. A canister sample and particlesize-distribution measurement were obtained coincident with each filter bag 

sample. The canister and size-distribution data are averaged when they are 

compared with the filter data.

The light-scattering coefficient (bscat) as measured by the integrating nephelometer, was the parameter selected to be representative of the plume boundaries.

Plume cross sections were created graphically by plotting the value of bscat every

2 seconds (130-m path length) for each altitude traversed. Plume center was

defined as that where bscat reached peak values. Multiple traverses at the same

altitude were averaged. In documented cases of substantial plume fanning with 

height, or with multiple plume cores, the cross sections were made logically 

consistent with the available data.

To calculate emission fluxes of any parameter, we assumed that the parameter

could be linearly scaled to bscat. High-resolution data (13 samples per second)

12

5. Flight Procedures

and Data Processing

5.1 Flight Procedures

5.2 Data Processing
13

Figure 7—A plot of the weighed filter mass concentration versus 

the light-scattering coefficient (bscat) with linear regression and 

the 95-percent confidence intervals for the Oregon data set.

were used for bscat averages, which were computed for times when the batch 

sampler switch was in the “fill” position. By using a least-squares fit, an algorithm

was derived for the relation between the average value of bscat and each flux

parameter.

In the cases of the mass fluxes derived from the filters and the mass monitor, 

separate algorithms were developed for the Washington and Oregon units. The

bscat cross sections were contoured, and the grid areas, or areas between bscat

contours, were determined. The cross sections were then divided elevationally 

by windspeed (which was interpolated from soundings taken with the pilot balloon

released closest to the time of the cross section). An average windspeed was 

determined for each grid area. The emission flux is given by:

Flux= Σi

(grid area)i x (windspeed)i x (average parameter concentration in grid area)i

where i indicates the bscat contour level.
14

Figure 8—A plot of the weighed filter mass concentration versus 

the light-scattering coefficient (bscat) with the linear regression 

and the 95-percent confidence intervals for the Washington data 

set.

Mass fluxes were derived from linear equations relating measurements of bscat to

the data from the weighed filters, the mass monitor (<2 μm in diameter) and the 

total aerosol volume (<43 μm in diameter). These relations are given in table 6.

Least-squares-fit linear regression equations on bscat were used to derive the 

mass flux by using data from the mass monitor and total aerosol volume. The 

mean mass concentration divided by the mean bscat value was also used to derive

the mass flux from the filter data. Six extreme values from the weighed-filter data

were excluded from analysis. FiRer data, mass monitor data, linear regressions,

and 95-percent confidence intervals are plotted in figures 7, 8, 9, and 10.

The relations between bscat and aerosol mass reported in the literature have 

usually been the result of a very limited data set, and the authors have merely 

made a ratio of bscat and aerosol mass and averaged the result (called the ratio

method). For example, in our earlier work we found values between 1.3 and 5.8

m2•g-1 for this ratio. White (1981) reports a range of values from 1.5 to 15.4 m2•g-1

for various sources. Anderson and others (1982) report bscat to-aerosol mass 

ratios of 1.9 to 3.4 m2•g-1 from a study similar to the present one. In the present

study, the mean value was 5.6 m2•g-1,with mean values of 4.1 and 6.9 m2•g-1 for

the Oregon and the Washington fires, respectively. The ratio method assumes 

that each particle contributes to bscat in proportion to its mass; in fact, we know this

is not the case. As described in more detail in section 6.2, the submicron particle

mass completely dominates bscat for the size distributions observed in this study.

5.3 Physical lnterpretation

of bscat Algorithms
15

Figure 9—A plot of the mass concentration as measured using the 

mass monitor instrument versus the light-scattering coefficient 

with the linear regression and the 95-percent confidence interval 

for the Oregon data set.

It is some combination of the distribution of supermicron particles and the inherent

noise of the data that produces the significantly nonzero intercepts of the algorithms

in table 6. That this departure from a 1:1 relationship is mathematically secure for the

filter data is indicated by the number of samples (44) and the satisfactory correlation

coefficient (0.78). The correlation coefficients are significantly improved if the data

are divided into sets for Washington and Oregon and six "extreme" values are

excluded. The correlation coefficients for the Washington and Oregon data sets are

0.92 and 0.88, respectively. No apparent basis for excluding the extreme values

exists other than they appear to be "outliers." Thus, for the bums studied, the bscat- linear-fit algorithm provides, in some ways, a superior predictor of smoke mass than

does the ratio method. The disadvantage of the algorithm is its questionable value at

the edges of plumes where bscat is small.
Figure 10—A plot of the mass monitor mass concentration 

versus the light-scattering coefficient (bscat) with the linear 

regression and the 95-percent confidence interval for the 

Washington data set.

For both reasons, and also because of the historical use of the ratio method, we

will use both the ratio method and the bscat-linear algorithm method in later sections. As an aside, the bscat-linear algorithm resulting from data of Anderson and

others (1982) is:

mass concentration (μg•m-3) = -0.042 (bscat•10-6•m-1) + 990 ;

16
17

Figure 11—Vertical cross section of the light-scattering coefficient 

in units of 10-3•m-1 measured perpendicular to the long axis of the 

plume from the prescribed burn on July 23, 1982 at 3.3 km from 

the burn. The heavy bars indicated the regions over which the 

batch sampler on the B-23 aircraft was operated. The cross 

section is based on airborne measurements taken during 

sequence 1 between 1606 and 1644 PDT.

with a correlation coefficient of -0.13. This result does not have predictive value

nor does it support a 1:1 relation between bscat and mass. This further indicates 

the need for a substantial data set to reduce statistical uncertainties.

Some of the data from the airborne measurements of the slash burns are presented in this section along with some preliminary interpretations.

Using the methods described in section 5.2, we assembled all the airborne 

measurements (except those clearly unsuitable because of nonperpendicular penetrations of the plumes or gross changes in burn characteristics) 

into cross sections of light-scattering coefficient. lllustrative examples are 

provided for each burn in this study.

July 23, 1982—This burn was on a hillside, just below a ridgeline in rough 

terrain. The plume initially rose nearly vertically through a boundary-layer 

inversion; it was then carried off horizontally, at an altitude of ≈1.7 km, by the

winds aloft. The plume was initially only ≈250 m thick (vertical dimension) with a

well-defined axial core (fig. 11). Additional fuel added to the burn after 1640 

Pacific Daylight Time (PDT) increased the depth of the plume to ≈400 m (fig. 12);

6. Preliminary Results

and Analysis

6.1 Characterization of Cross

Sections of the Plumes
18

Figure 12—Vertical cross section of the light-scattering coefficient 

in units of 10-3•m-1 measured perpendicular to the long axis of the

plume from the prescribed burn on July 23, 1982 at 3.3 km from 

the burn. The heavy bars indicated the regions over which the 

batch sampler on the B-23 aircraft was operated. The cross 

section is based on airborne measurements taken during 

sequence 2 between 1640-1814 PDT.

Figure 13—Vertical cross section of the light-scattering 

coefficient (in units of 10-3•m-1) measured perpendicular to the 

long axis of the plume from the prescribed burn on July 23, 1982, 

at 3.3 km from the burn. The heavy bars indicate the regions over 

which the batch sampler on the University of Washington B-23 

aircraft was operated. The cross section is based on airborne 

measurements taken during sequence 3 between 1719 and 1745 

PDT.
Figure 14—Vertical cross sections of the light-scattering 

coefficient (in units of 10-3•m-1) measured perpendicular to the 

long axis of the plume from the prescribed burn on July 23, 1982, 

at 3.3 km from the burn. The heavy bars indicate the regions over 

which the batch sampler on the University of Washington B-23 

aircraft was operated. The cross section is based on airborne 

measurements taken during sequence 4 between 1744 and 1814 

PDT.

but by 1720 PDT, the plume had stabilized back to a thickness of ≈280 m. By 

1720 PDT, the plume was substantially more complex (fig. 13), with light winds 

and terrain features introducing portions of the plume from earlier in the day into 

the cross section. The secondary core of the plume, located at an altitude of 

1.65 km and 1.2 km to right of center (fig. 13) was part of the "old" plume. During

post-analysis, we removed from the data set encounters with smoke that were 

obviously separated from the main plume. In this case (and the following), where

"old" smoke merged with "new" smoke, we were unable to objectively partition 

the data. Consequently, this cross section and the following (fig. 14) tend to 

exaggerate the emission fluxes. When the plume sketches and photographs 

from the patrol aircraft aloft become available, it may be possible, through further

analysis, to remove this ambiguity.

July 24, 1982—This plume was low initially and did not rise above local ridgelines, which made airborne sampling nearly impossible. An attempt was made to

rectify this by adding more fuel; this caused the plume to rise to more than 3500 

m. Before a series of airborne cross-sectional measurements could be completed, however, the plume collapsed to much lower altitudes. A steady-state 

assumption for this burn, therefore was not justified, and no cross sections were

compiled.

19
20

Figure 15—Vertical cross section of the light-scattering 

coefficient (in units of 10-3•m-1) measured perpendicular to the 

long axis of the plume from the prescribed burn on July 25 ,1982, 

at 3.3 km from the burn. The heavy bars indicate the regions over 

which the batch sampler on the University of Washington B-23 

aircraft was operated. The cross section is based on airborne 

measurements taken during sequence 2 at 1021 and 1041 PDT.

July 25, 1982—This burn produced a good, stable plume for about 2.5 hours. 

The cross sections all look similar to the one shown in figure 15. Only sequence 3,

taken between 1037 and 1054 PDT, departed from a completely stableappearance; the plume contained a significant amount of smoke ≈300 m below the 

average base of the plume at ≈900 m at mean sea level (MSL).

July 26, 1982—Stable weather conditions allowed good measurements to be 

obtained on July 23 and 25. On July 26, as broken cirrus and cirrocumulus and 

towering cumulus clouds on the horizon to the east invaded the sky, sampling 

conditions deteriorated. Despite changes in atmospheric stability, seven cross 

sections of good quality were obtained in the plume from this burn. Only sequences 

3 and 4 (from 1114 to 1159 PDT) showed significant deviations from an otherwise 

visually steady plume. The thickness of the plume decreased during sequence 3 and

increased during sequence 4; the other cross sections look very much like the one

shown in figure 16.

September 15, 1982—This was the first burn in Washington, and it was 

significantly larger than any of the Oregon burns. The plume was visually rather 

stable and steady. The cross sections show a small plume initially, followed by a 

very steady period from 1500 to nearly 1600 PDT, followed, in turn, by a slowly 

shrinking plume. Figure 17 is representative of the large and complex plume 

encountered.
21

Figure 16—Vertical cross section of the light-scattering 

coefficient (in units of 10-3•m-1) measured perpendicular to the 

long axis of the plume from the prescribed burn on July 26, 1982, 

at 3.3 km from the burn. The heavy bars indicate the regions over 

which the batch sampler on the University of Washington B-23 

aircraft was operated. The cross section is based on airborne 

measurements taken during sequence 5 between 1157 and 1219 

PDT.

September 23, 1982—This plume showed large departures from visual 

steady state. This situation was further complicated by a substantial turning of 

the wind direction with height within the range of altitudes occupied by the 

plume. Obscuring of surface terrain features by smoke near the burn and offscale readings of the light-scattering coefficient at a range of 3.3 km prompted 

us to move to a range of 6.6 km to obtain cross-sectional measurements. The

results depicted in figure 18 are typical of the complex plume encountered.

Summary—The cross sections shown in figures 11 through 18 are important in

quantifying the nature of the plumes. Further quantitative information is provided 

in table 7, which lists the average values of bscat between contours (shown in the

cross sections) and the area between that contour interval multiplied by the wind

speed (the volume flux of air) for all valid cross sections. The information in table 7

can be used to compute the emission flux of any parameter that can be related to

bscat.
22

Figure 17—Vertical cross section of the light-scattering 

coefficient (in units of 10-3•m-1) measured perpendicular to the 

long axis of the plume from the prescribed burn on September 15, 

1982, at 3 3 km from the burn. The heavy bars indicate the regions 

over which the batch sampler on the University of Washington B-23 

aircraft was operated. The cross section is based on airborne 

measurements taken during sequence 4 between 1525 and 1610

PDT.

Figure 18—Vertical cross section of the light-scattering 

coefficient (in units of 10-3•m-1) measured perpendicular to the 

long axis of the plume from the prescribed burn on September 23, 

1982, at 6.6 km from the burn. The heavy bars indicate the 

regions over which the batch sampler on the University of 

Washington B-23 aircraft was operated. The cross section is 

based on airborne measurements taken during sequence 3 at 

1608 and 1647 PDT.
In a previous series of airborne measurements obtained in the plumes from prescribed burns (Stith and others 1981), it was noted that both the number and 

the mass distributions of the particles in the plume are generally dominated by a

concentration peak at -0.1 μm diameter; a much less prominent peak at ≈0.5 μm

also occurs. With the instrumentation available in 1981, information on particles

>10 μm present in number concentrations down to ≈0.1 cm-3 was uncertain. With

the instrumentation available for the present study, relative measurements on 

particles >10 μm can be obtained at concentrations down to ≈0.1 cm-3. The availability of new instruments to measure particle sizes (see section 2) extended our

measurements to particles ≈3000 μm in diameter that were present in concentrations down to ≈10-5•cm-3. These new capabilities resulted in a revision in our

view of the role of supermicron particles in smoke from prescribed burns.

Particle size distributions--The distribution of particle sizes shown in figure 

19 illustrates many of the features typical of the smoke from the prescribed burns

in this study. The distribution shown in figure 19 was obtained on July 23, 1982, 

at a range of 3.3 km for the burn and near the plume center on traverse “C.”

As discussed in section 2.2, the use of the batch samples should resolve any 

timing difficulties arising because the four instruments for measuring particle sizes

(EAA, ASAS, LAS, Royco 245) operate on different time sequences. Some loss 

of data accuracy nevertheless can occur through operational errors. For the data

obtained to be considered valid, we required smooth transitions between measurements from the various instruments that measured particle sizes. Due to 

counting statistics and sedimentation, each instrument was most accurate for

small-sized particles and generally least valid for large-sized particles. The most

common concerns about the data were poor transitions between measurements

obtained with the EAA and ASAS (about 20 percent of all cases) and a rough 

transition between measurements from the ASAS and LAS. lnstrument transition

for these most regularly used particle-measuring instruments occurred at diameters of about 0.14, 0.85, and 6.4 μm. The instruments in the particle-measuring system produce, in total, concentrations for 100 different-sized, but not 

entirely discrete, particle intervals (see table 1 and fig. 2). To reduce the data, 

original data were merged into one 30-point spectrum for each sample. A correction factor also was applied to concentrations in several of the size ranges after

we found that a laser was misaligned in one of the instruments. (This misalignment caused a negligible error in measuring particle size but a significant error in

concentration of the particles.)

The measured particle-size distributions showed similar shapes and gross 

features throughout the duration of each burn and for all burns studied (for example, fig. 20). The predominant concentration peak at 0.15 μm diameter and volume peak at ≈0.25 μm diameter agree well with those of Stith and others (1981)

who found corresponding values of 0.1 and 0.3 μm Measurements from the 

EAA show concentrations still increasing below 0.01 μm (the limit of this instrument), indicating the possibility of a (nucleation) peak in the number distribution

23

6.2 Some Characteristics 

of the Particles 

in the Plumes
24

Figure 19—Number concentrations versus size of particle 

measured in the plume from the prescribed burn at 1742 PDT on

July 23, 1982, at 3.3 km downwind of the burn (solid line). The

dashed line shows the average ambient particle size distribution

on that day.
below 0.01 μm. Because the cumulative particle number from the EAA is in 

reasonable agreement with the “total” aerosol concentration as measured by the

Aitken nucleus counter, the peak must be near 0.01 μm. Furthermore, most of

In contrast to the spectra of Stith and others (1981), the present spectra lacked a

small secondary concentration peak at 0.5 μm diameter. This may have been an

artifact of the aerosol system used by Stith and others (1981). Our new system 

had an instrument transition point a little beyond (0.65 μm) that of the old system

and made use of the ASAS, which has smaller sizing intervals. Our current data

did not support a concentration peak at 0.5 μm diameter.

The most dramatic difference between the present measurements and those

reported by Stith and others (1981) was in the supermicron particle volume distribution, for which our new particle-sampling system provided superior resolution

for particles with diameters up to ≈45 μm Figure 20 shows that in our current 

data, the supermicron particle peak is not resolved; the volume continues to increase with increasing size to the limit of the measurements. Our previous smoke

data showed a minor mass peak at ≈10 μm and the vast majority of the mass located in the submicron peak. The higher concentrations of supermicron particles 

measured in this study, as compared to measurements by Stith and others 

(1981), are almost certainly due to improved sampling techniques. These new

observations affect estimates of total suspended particulates.

A substantial fraction of the particles in the plumes had diameters >45 μm; this 

was supported by the pilot observing that we were collecting millimeter-sized

pieces (still smoldering?) under the windshield-wiper blades of the aircraft. The

shapes of some of these particles are shown in figure 21. The largest particle in

this sample was about 4 mm long.

The other three laser cameras aboard the B-23 also detected the large particles.

Although the counting statistics of these three cameras were only just satisfactory, the shape of the distribution can be seen in the raw data plot taken near

plume center at 1427 PDT on September 15, 1982 (fig. 22). The measurements

from the instruments agree reasonably well with simultaneous measurements

obtained from the aerosol system, but there is a change in the slope at the overlapping intersection of the two data sets (fig. 23). The point is, these curves show

that the peak in the volume of the supermicron particles is still not resolved even

by our extended size measurements; the total volume of the particles is still increasing for particles above 1000 μm in diameter. Although the submicron particles dominated visibility reduction by the plume and the impact of the plume 

over large distances, it was clear that at 3.3 km downwind of the prescribed burns

that we studied, the supermicron particles dominated the total mass of particles in

the plume. This result had a significant effect on our interpretation of the aerosol 

filter data (see section 6.5).

25
26

Figure 20—Number concentrations versus size of particles

measured near the center of the plume and 3.3 km downwind of

the burn on July 23, 1982, at 1636 PDT (heavy solid line), 

1741 PDT(dashed line) and 1759 PDT (solid line). The ambient

particle size distribution is also shown (dotted line).
27

Figure 21—Shadow images of airborne particles observed with

the laser camera in cross-sectional sequence 2 through the

plume from the burn, ≈1727 PDT, September 15, 1982. For probe

4, the vertical frame size is 800 μm; for probe 5, it is 3200 μm.
28

Figure 22—Number concentration versus size of particles 

measured with a laser camera on the University of Washington 

B-23 aircraft near the center of the plume 3.3 km downwind of the

burn, 1427 PDT, September 15, 1982.
29

Figure 23—Number concentration versus the size of particles 

from the burn on September 15, 1982. Measurements were 

obtained with the aerosol system near the top of the plume at 

3.3 km downwind of the bum at 1427 PDT (heavy line) and at 

plume center at 1727 PDT (lighter line). The dashed line 

extensions are measurements from the laser cameras.

Average characteristics of the particle-size distributions—The 

characteristics of the particle-size distributions are best seen in the averaged and

summed characteristics of the mean number diameter (MND) of the particles, their

mean volume diameter (MVD), and the total particle volume (TPV) for particles 

<43 μm in diameter. Plots of these parameters, as a function of time after burn 

ignition, reveal a number of significant differences among the burns that we 

studied.

Figure 24 indicates the generally steady-state nature of the plume from the burn 

on July 23, 1982, for 50-140 minutes after ignition; the MND is steady between 

0.02 and 0.04 μm, and the TPV is steady near 300 μm3•cm-3 The MVD is more 

variable, ranging from 3 to 10 μm, and is evidently correlated with the TPV. The 

altitude of the plume center rose by less than 150 m during this period. In contrast, the “well-behaved” plume occurring on July 25, 1982, showed a general

increase in MVD and TPV as a function of time after ignition (fig. 25), although it

gained substantially in altitude as the burn progressed. This behavior was repeated on July 26, 1982 (fig. 26). In both cases, the MVD was initially
30

Figure 24—Characteristics of the particles near the center of the 

plume on traverse “C” 3.3 km downwind of the burn on July 23, 1982, as 

a function of time after ignition.

≈1 1μm and increased to ≈5 μm by about 2 hours after ignition. The MND’s show 

little variation. The larger burn in Washington on September 15, 1982 (fig. 27)

shows far more variability, despite a visually steady plume.
31

Figure 25—Characteristics of the particles near the center of the 

plume on traverse “C” 3.3 km downwind of the burn on July 25, 

1982, as a function of time after ignition.

The second Washington burn on September 23, 1982, was studied at 6.6 km

downwind (fig. 28). Visually, the plume was less steady than the plume on September 15; again, there was only slight correlation between MVD and TPV. The

MVD decreased throughout the duration of the burn; it had an initial value ≈1.5

μm and finished at 0.5 μm, with a discontinuity at ≈100 minutes after ignition 

when both MVD and TPV increased sharply. The MND shows signs of being 

anticorrelated with MVD.

lnteresting features of the data sets are the two cases of clear positive correlation

among MVD, TPV, and plume rise and the other three cases in which these correlations are not evident. In the two cases of positive correlation, a relation seems

to occur between the intensity of the burn (as indicated by plume rise) and the lofting of ever-larger debris into the plume. The fact that there are weak indications

that the MND decreases as MVD and TPV increase (see the July 25 and 26

cases) suggests that combustion efficiency also played a role. As the intensities 

of the burns increased, more complete combustion produced smaller particles, 

but simultaneous increases in the velocity and turbulence of the air increased the

concentrations of partially burned fuel and other debris in the plumes.
32

Figure 26—Characteristics of the particles near the center of the 

plume on traverse “C” 3.3 km downwind of the burn on 

July 26, 1982, as a function of time after ignition.

Apparent density of the particles—Simultaneous measurements of the 

particle size distribution (from which the particle volume distribution can be inferred), the particle mass distribution (with the cascade microbalance), and the mass

of particles <2 μm (with the mass monitor) allow determination of the apparent 

density of the particles. Because the uncertainties in the responses of the 

instruments are less for smaller sized particles, we limited our calculations to 

particles with diameters <1.9 μm.

The equations resulting from linear fits to the data are given in table 8. The 

apparent particle density obtained from the mass monitor data was 0.98±0.03

g•cm-3, and that from the microbalance data was 0.86±0.09 g•cm-3. Using similar

instruments (the same mass monitor) and techniques, Stith and others (1981)

determined a particle density of ≈1 g•cm-3 in the plumes from the prescribed 

burns that they studied. Some systematic uncertainties may remain in the particle-density determinations (perhaps greater than the quoted standard deviations) because of the broad mix of instruments used. For this reason, we use 

the term “apparent density.”

Because the correlation between particle volume distributions, derived from the

particle size measurements and the particle mass distributions for particles <2 μm

in diameter, as measured by the cascade microbalance, was barely satisfactory

(correlation coefficient = 0.66; table 8), it is illustrative to compare the particle 

volume distributions with the mass distributions measured by the cascade
33

Figure 27—Characteristics of the particles near the center of the plume 

on traverse C” 3.3 km downwind of the burn on September 15, 1982, as a 

function of time after ignition.

microbalance over the full range of particle diameters from 0.05 to 25 μm To 

convert the cascade microbalance distributions to volume distributions, we divided by a (rounded-off) particle density of 1.0 g•cm-3. (We will use this density in 

the remainder of this report.) Some results are shown in figure 29, where we see

that the volume distributions derived from cascade microbalance measurements

reproduce the submicron peak detected by the system for measuring particle 

sizes. The very small sample flow for the cascade microbalance prevents it from

collecting a weighable sample for particles >5 μm, however.

We believe that the measurements of the size spectra of particles converted to a

mass distribution, by using a derived apparent particle density, is a more valid approach to obtaining size-segregated mass distributions in the plumes than are the

measurements from the cascade microbalance.
Figure 28—Characteristics of the particles near the center of the plume 

on traverse “C” 3.3 km downwind of the burn on September 23, 1982, as a 

function of time after ignition.

The effect of particle density on the mass of particles produced by fire conditions

is not resolved here. Recent data suggest an increase in the elemental carbon

content from near zero for smoldering fires to 20 percent for very high-intensity

fires. Ward and Core (1984) report the percentage mass of elemental carbon 

(specific gravity 1.88 to 2.25) and trace elements of K and CI to be proportional to

fire intensity. Although we concluded that the density of the aerosol from these

prescribed fires is about 1 g•cm-3, the variance over the course of a fire may be a

function of fire intensity.

Aerosol elemental analysis—ln addition to weighing the filters, Crocker

Laboratory performed an elemental analysis by Proton-lnduced X Ray Emission

(PIXE). We have applied the matrix correction factors for Na, Al, Si, and CI, which

had correction factors >10 percent; all other elements had correction factors 

<10 percent, which were not applied. These data are shown in table 9 in a form

suitable for factor analysis.

As expected, the filters show high concentrations of Ca and K (from the combusted biological materials). Significant S is emitted, although we have never seen 

significant SO2 emitted from a slash fire.

34
Figure 29—Volume concentration versus size of particles 

measured with the aerosol sizing system near the center of the 

plume from the burns: (a) 0954 PDT, July 25, 1982; (b) 1605 PDT, 

September 23, 1982; (c) 1718 PDT, September 23, 1982; and (d) 

1700 PDT, September 23, 1982. The dashed lines show results 

derived from the cascade microbalance impactor (mass/density 

of particles).

In addition to the 6-L air samples collected in the 500-L polyethylene bag sampler

for LEMSCO (the samples were used to determine CO and COp concentration in

the plumes), a limited number of 6-L air samples were collected after passing

through a stainless steel sample loop (see section 2.3). The later samples were

analyzed for hydrocarbons and fluorocarbons by R. Rasmussen at OGC to determine if specific hydrocarbons or fluorocarbons could be used as plume tracers.

These samples also served as quality control checks on the more numerous 

samples collected in the polyethylene bag for LEMSCO, as the stainless steel 

sample loop is much less subject to contamination than a polyethylene bag. 

Besides the intercomparison among samples collected from the two sampling 

systems, a limited number of samples collected from the polyethylene bag were

analyzed by OGC after they had been analyzed by LEMSCO. Comparison of 

these samples allowed an evaluation of the LEMSCO system against what is 

essentially the standard reference system for such analyses (that is, gas chromatograph/mass spectrometer; gas chromatograph/electron capture; and gas 

chromatograph/flame ionization detector).

35

6.3 Analysis and 

Cross Comparisons

of Bulk Air Samples
Table 10 lists the results of the LEMSCO and OGC analyses on the same samples

collected with the polyethylene-bag sampler from the B-23. There is good agreement between the two data sets for CH4, CO, and CO2 with the concentrations

measured by LEMSCO and OGC generally within about 10 percent of each other.

But because of the relatively slight difference in concentrations of the CO2 in the

plume and the ambient air, a 10 percent error in CO2 measurements can have a

substantial impact on the derived CO2 flux in a plume (see appendix A and tables 

4 and 5). Furthermore, one of the two samples for which total nonmethane hydrocarbons (TNMHC) concentrations could be compared (sample 238) showed a

marked discrepancy between the LEMSCO and OGC measurements, with the 

LEMSCO system measuring a TNMHC concentration ≈65 percent higher than 

the OGC measurement (despite the fact that the LEMSCO measurement does 

not include C2 hydrocarbons and the OGC measurement does). Although it is 

conceivable that reactive hydrocarbons may have appreciably decayed between 

the LEMSCO and OGC measurements (reactive compounds such as isoprene 

were virtually absent from the OGC analysis), it is unlikely that this accounts for a

discrepancy of this magnitude. Unfortunately, the limited number of samples 

available for comparison precludes any definitive comparison of the two measuring systems. Table 11 compares measurements made by LEMSCO on samples 

collected in the polyethylene bag with those made by OGC on samples collected

using the stainless steel sampling loop. The CH4 and CO2 measurements were in

reasonable agreement, but both the CO and TNMHC concentrations obtained 

from the polyethylene bag were generally significantly greater than those obtained from the canisters. This is almost certainly a result of contamination and suggests that the TNMHC concentrations measured by LEMSCO should be discarded.

The CO concentrations measured by LEMSCO, although showing somewhat 

less disparity with the measurements for samples collected with the stainless 

steel sampling loop than with those shown by the TNMHC concentrations, should

also be used with caution.

Although a rather large number of trace compounds were elevated over ambient

levels in the plumes from the bums (for example, C2H4 and C2H2), the compounds most consistently elevated were the halocarbons (CH3I and CH3CI). This

was the case both for samples collected by the polyethylene bag sampler and 

those collected by the stainless steel loop. Enhancements in concentrations of 

these trace compounds in the plume ranged from a factor of 1.5 to a factor of 10 

in both the Oregon and Washington field studies. This suggests that these 

compounds could be used as conservative tracers of slash burn smoke by using 

the halocarbons (CH3I and CH3CI). This was the case both for samples collected 

by the polyethylene bag sampler and those collected by the stainless steel loop.

Enhancements in concentrations of these trace compounds in the plume ranged

from a factor of 1.5 to a factor of 10 in both the Oregon and Washington field 

studies.

36

6.4 Plume Tracers
Principle of the method for determining particle emission factors—

The principle of the method for determining particle emission factors for fires is to

measure the particle emission flux and to divide this by the fuel consumption rate.

Because we did not have information on the rates of fuel consumption, this method was not used for this report. Instead, we determined particle emission factors 

by a carbon-balance method. This method requires measurements of the concentrations of carbonaceous gases and particles across a section of the plume 

and simultaneous measurements of the horizontal wind through this cross section. The procedure for the emission factor (EF) for particles (over any specified 

size range) is defined as:

EF = mass flux of particles along the plume

fuel consumption rate

Therefore:

EF =P•A•V • F (1)

where P is the average mass concentration of the particles across a section 

of the plume, A is the cross-sectional area of the plume, V is the horizontal wind

speed through this section, and F is the fuel consumption rate. Because the 

carbon burned per unit of time (CB) is given by:

CB = F•CFw ; (2)

where CFw is the fractional mass of carbon in the fuel, we have from (1) and (2):

EF = P•A•V•CFw (3)

CB

If deposition of the particles is negligible and the plume is in steady state:

CB = [(P•CFp) + (CO2•CFCO2) + (THC•CFTHC) + (CO•CFCO)]V•A ; (4)

37

6.5 Particle Emission 

Factors
where, CO2, THC, and CO are, respectively, the average mass concentrations of

C02, total hydrocarbons (THC), and CO across the section of the plume; and 

CFp, CFCO2, CFTHC, and CFco are the fractional masses of carbon in the airborne

particulates, CO2, THC, and CO, respectively. From(3) and (4):

EF = P•CFw (5) 

(P•CFp) + (CO2•CFCO2) + (THC•CFTHC) + (CO•CFCO) (5)

In (5), the bar over the concentrations indicates an areal average over the plume

cross section. If the particles and gases in the plume are mixed in a uniform ratio,

the areal averages may be replaced by averages along the flight path (which are

what are available in practice; see section 6.1). Using the airborne measurements

and taking CFw = 0.497 (Byram 1959) and CFp = 0.50 (Ward and Hardy 1984), we

can determine particulate emission factors from (5).

We will discuss below the results of applying this method to determine the 

emission factors for total suspended particulates and for particles in several size

ranges for six of the burns studied.

Emission factors for total suspended particulates derived from 

filter measurements—We applied the above procedures to the canister data 

analyzed by LEMSCO for carbonaceous gases and the total suspended particles

from weighed filters (part of the Crocker Laboratory analysis). These samples 

were obtained simultaneously from the large bag sampler, although most of the 

filter samples represented the average of several bag samples. Each bag sample

that was analyzed had a canister sample that was averaged over the same period

for which the filter was exposed.

The Oregon burns (missions 1-4) yielded 18 estimates of the emission factor for

total suspended particulates. The Washington burns (missions 5 and 6) produced an additional 20 estimates. These derived emission factors for total 

suspended particulates are listed in table 12 (the data used to calculate these 

emission factors are given in appendix A).

38
39

Figure 30—Emission factors for TSP as a function of time after 

ignition for the Oregon burns.

Figure 31—Emission factors for TSP as a function of time after 

ignition for the Washington burns.
When the emission factors are plotted as a function of time after ignition, the 

rather similar-sized Oregon burns show a clear pattern (fig. 30). At about 50 

minutes after ignition, the emission factors ranged from ≈3 to 9 g•kg-1 (0.3 to 0.9

percent), they reached peak values of ≈11 to 15 g•kg-1 (1.1 to 1.5 percent) about

125 minutes after ignition, and they appeared to decline slightly between ≈125 to

150 minutes after ignition. Interestingly, the emission factors peaked at about the

same time as the centers of the plumes reached their maximum heights (see section 6.1). The emission factors for total suspended particulates for the larger

Washington burns show little functional tendency with time (fig. 31).

The emission factors for total suspended particulates for the Oregon burns 

averaged 11.0±3.5 g•kg-1 (1.1±0.4 percent) compared to an average of 

13.3±3.4 g.kg-1 (1.3±0.3 percent) for the Washington burns.

In assessing the accuracy of the emission factors for total suspended particulates

listed in table 12, the following points should be considered:

1. All filters noted by the Crocker Laboratory to have been damaged or to have 

had missing portions were excluded from the analysis. Data loss from this source

was severe only for July 26, 1982 (mission 3).

2. Measurements of THC, NMHC, and CH4 made by LEMSCO were of uneven

quality, both in consistency and accuracy (see sections 4.2 and 6.3). Most notable was the failure of NMHC + CH4 to equal THC (even when the C2 compounds,

thought to be excluded in the LEMSCO analysis, were estimated and included in 

the LEMSCO results). Our estimates of carbon content in hydrocarbons were

obtained by using the THC for missions 2, 3, 4, and 6 and NMHC + CH4 for mission 1. The THC and NMHC measurements taken with Mylar bags on mission 5 

were obviously faulty4 and showed no correlation with emissions. Calculations for

mission 5 were made without hydrocarbon estimates. The impact of these uncertainties on the calculation of the emission factors was only a few percentage 

points.

3. The uncertainty in the CO2 fluxes (discussed in section 6.3) was potentially a

larger problem than the THC problem discussed above, but it was not well 

quantified.

4. The mass collection efficiency of the filters was better than 99 percent over the

entire submicron range. The primary uncertainty in estimating the emission 

factors for total suspended particulates may be the result of uncertainties in the 

collection efficiencies of large particles on the filters. The filter sample train for 

the bag sampler should have a reasonably high collection efficiency for particles

4 Because of a lack of stainless steel canisters, Mylar bags were 

substituted for the canisters on mission 5.

40
up to about 10 μm diameter. While sampling at the very short range of 3-4 km, we

encountered unexpectedly high concentrations of ash particles and other debris

larger than 100 μm (see section 6.2). Because of its rapid removal from the atmosphere by sedimentation, this material would not normally be considered a part 

of the total suspended particulates, but some small fraction of this material likely

was captured by the filters.5

The results, shown in table 13, are compared to the emission factors for total 

suspended particulates calculated from the filter data. Average emission factors 

are as follows: for total suspended particulates (filters) 12.2±3.6 g•kg-1, for particles <43 μm in diameter 6.0±3.4 g•kg-1, and for particles <2 μm in diameter 

4.1±1.5 g•kg-1 from the mass monitor and 3.7±1.7 g•kg-1 from the cascade impactor measurements. The largest burn was mission 5; this burn also produced 

the best visual steady-state plume.

The average emission factors for all three size categories were higher in this burn

than in the other five burns; they were for total suspended particulates 13.4±3.7

g•kg-1, for particles <43 μm in diameter 8.7±3.8 g•kg-1, and for particles <2 μm in

diameter 4.8±1.4 g•kg-1.

Calculations based on total suspended particulate (filter) measurements yielded 

the largest emission factors and tended to confirm the role of particles >43 μm in

diameter in determining the weight of the filters. Comparisons of emission factors

derived from the filter data with those calculated for particles <43 μm in diameter,

from mass monitor, and from cascade impactor data produced linear correlation

coefficient of 0.85, 0.81, and 0.65, respectively. The correlation coefficient 

among emission factors for particles <2 μm in diameter (mass monitor) and for 

particles <43 μm in diameter was 0.76; a comparison of emission factors from the

mass monitor and cascade impactor (both particles <2 μm in diameter) produced a

correlation coefficient of 0.58.

Because we are uncertain about the upper limit of the particles collected on the 

filters, we conclude that the emission factors and values of total suspended 

particulates derived from the filters must be used with caution. Measurements

obtained from the other techniques discussed above, although they may be 

more closely defined, also have accuracy limitations. We emphasize that none of

the estimates for emission factors and TSP listed in table 13 represent the actual

total particulate in the plume.

5 We suspect that the larger particles collected were primarily the 

products of the breakup of the supermicron ash particles in the 

intake tube. Large particles inducted intact would have a very low 

probability of being collected on the filter because of impaction or 

sedimentation in the sample train. Resuspension of supermicron 

particles within the bag at the next fill cycle and turbulent or 

mechanical breakup into smaller particles, and hence their 

appearance in subsequent samples, are also possibilities.

41
Figure 32—Particle mass fluxes derived from particle 

mass measurements <43 μm (solid lines) and particle 

mass measurements <2 μm for the Oregon burns.

In another study (Ward and Hardy 1984), emission factors for particulate matter

were determined by using samplers suspended from cables strung between 

towers over prescribed fires. The size-selective emission factors for total particulate matter and particulate matter <2.5 μm in mean mass diameter are in reasonable agreement with the results reported here. Ward and Hardy’s measurements show the difference between total particulate matter and particulate matter

<2.5 μm, to be a function of fire intensity (r=0.90). Most of the emissions sampled 

for this paper originated from the flaming combustion phase before the onset of 

the collapse of the convection column, when the difference between the emission factor for total suspended particulates and that for particles <2 μm in diameter

would likely be at a maximum.

Although it will not be possible to calculate emission factors using the flux method

until the fuel consumption data are available, this section describes the first step,

namely, the calculation of particle mass fluxes. As for emission factors, we have 

calculated particle mass fluxes for total suspended particulates (from the filters), 

for particles <43 μm (from the UW particle-size measuring system, assuming a 

particle density of 1 g•cm-3) and for particles <2 μm (from the mass monitor).

The particle mass fluxes for total suspended particulates (TSP) were calculated by

using the appropriate value of the “volume flux of air,” as listed in table 7, together

with the appropriate algorithms relating bscat and TSP particle mass concentration 

for “all data” as given in table 6. These results are shown in the fourth column of

42

6.6 Particle Mass Fluxes
Figure 33—Particle mass fluxes derived from particle mass 

measurements <43μm (solid lines) and particle mass 

measurements <2 μm for the Washington burns.

table 14. The particle emission fluxes for TSP were also calculated with the ratio

method by using the appropriate ratios of bscat to aerosol mass for the Oregon 

and Washington fires (see section 5.3). The results are listed in the fifth column 

of table 14. Shown in the last two columns of table 14 are the particle mass fluxes

for particles <43 μm and <2 μm in diameter as derived from the particle spectra 

and mass monitor data, respectively. The particle mass fluxes for the total suspended particulates are about twice those for particles <43 μm in diameter and

about three times for particles <2 μm in diameter.

Plots of the particle mass fluxes for the burns in Oregon (fig. 32) and Washington

(fig. 33) show a number of interesting features when compared to the time histories of particle volume at plume center (see section 6.2) and to the emission factors (section 6.5). Figure 32 shows that the peak particle mass flux for the Oregon

burns occurred 80-100 minutes after ignition; the total particle volumes at plume

center and the emission factors tended to peak later in the burn. For both the

Oregon and Washington burns, the particle volume (<43 μm) at plume center was

not a very good predictor of the integrated flux over the cross section. 

The following topics deserve further study:

1. The airborne data collected on July 24, 1982, were only partially analyzed

because visual observations indicated that a steady-state assumption was not 

warranted. Despite this limitation, some good data were obtained on this flight.

These data need further analysis.

43

7. Topics For Further

Study
because visual observations indicated that a steady-state assumption was not 

warranted. Despite this limitation, some good data were obtained on this flight.

These data need further analysis.

2. Data collected on July 25, 1982, were not fully analyzed (despite the excellent

plume on this day) because the filters were damaged. The remaining data should 

be fully analyzed.

3. In determining the particle emission factors presented in this report, we used 

CO2 and CO measurements from the canister samples; however, continuous 

measurements of C02 and CO were also made. Calculations of particulate 

emission factors using these continuous measurements are needed. By using 

the continuous data, we could obtain measurements of particle emission factors 

in all cases where particle samples were obtained rather than just those where a

canister sample was available. Accuracy would not be improved because canister

samples would be needed to calibrate the CO2 data (see section 4.2), but this

would result in an approximate doubling of the number of estimates of the 

emission factors.

4. The nitrogen oxides and ozone data have not been analyzed, although they

appear to be of good quality. This should be done.

5. The measurements of the particle size distributions from 0.01 to 4500 μm in

diameter permit particle fluxes to be determined over any reasonable number of

size intervals for all of the cross sections (independent of bscat or other continuous measurements). These fluxes have not been calculated, but this could 

be done to assess the mass of particles in the plume by size fractions.

6. We have made only limited use of the elemental analysis of the material 

collected on the filters. The data are now organized for factor analysis, which 

could be useful in establishing elemental “fingerprints.”

7. When the fuel consumption rates become available, independent estimates 

need to be made of the emission factors for the burns; these can then be compared with those determined from the carbon-balance technique used in this 

report.

8. The yarding and ignition characteristics of the burns need to be compared with

the information about the plumes provided by the airborne measurements.

9. Additional knowledge is needed on the density of the material in the emissions

over various particle size intervals to compute more accurately the mass fluxes of

aerosols from the particle volume distribution data.

In this report, we have presented the results of airborne measurements on the 

particulate and gaseous emissions from a series of prescribed burns of forest

residues. The measurements were used to obtain quantitative data on plume

44

Study

8. Conclusions
dimensions, particle size distributions, particle densities, and size-dependent particle

emission fluxes and emission factors.

Our airborne measurements of particle size distributions produced some 

surprises. As in previous studies, a peak in the mass concentration of particles 

centered around particles 0.25-0.3 μm in diameter. Particle concentrations were

dominated by large numbers of Aitken nuclei (median number diameter ≈0.15 

μm). Although submicron particles dominated the visibility characteristics of the

plumes, they did not dominate the total emissions from the burns. Even more 

surprrsing was the observation that the mass flux 3.3 km downwind of the burn 

may have been dominated by millimeter-sized debris.

The effective density of the submicron particles in the plumes was determined by

two independent techniques to be 0.86±0.09 g•cm-3 and 0.98±0.03 g•cm-3. 

Some uncertainty exists as to the absolute accuracy of these determinations.

Recent studies suggest that the density of the particles may be a function of fire

intensity.

Emission factors have been determined, by using the carbon-balance method, 

for total suspended particulates (with some uncertainty as to the upper limit for 

particle size), particles with diameters <43 μm, and particles <2 μm in diameter. 

The derived average emission factors, based on numerous measurements in six

burns, were 12.2±3.6 g•kg-1 for the total suspended particulates, 6.0±3.4 g•kg-1

for particles <43 μm in diameter, and 4.1+1.5 g•kg-1 and 3.7±.7 g•kg-1 from two

independent measurements of particles with diameter <2 μm. The Washington

burns showed no significant trend with time, but the Oregon burns showed 

marked and consistent temporal variations.

Particle mass fluxes for total suspended particulates, particles <43 μm in 

diameter, and particles <2 μm in diameter ranged from 0.1 to 2.4 kg•s-1, 0.1 to 1.1

kg•s-1, and 0.1 to 0.8 kg•s-1, respectively, for the smaller Oregon burns, and 1.1 

to 11.7 kg•s-1, 0.6 to 7.0 kg•s-1, and 0.4 to 4.1 kg•s-1 respectively, for the larger

Washington burns.

Centigrade (°C) 1.8 degrees Fahrenheit + 32

centimeter (cm) 0.3937 inch

cubic centimeter (cm3) .061 cubic inches 

garam (g) 0.03527 ounce

hectare (ha) 2.471 acres

kilometer (km) 0.6214 statute mile or 0.5396 nautical mile

liter (L) 33.814 ounces (liquid) or 6.00353 ft3

45

English Equivalents
meter (m) 39.37 inches

metric ton (t) 2204.623 pounds

micrometer ( μm) 1•10-6 meters

millimeter (mm) 0.0394 inch

square meter (m2) 10.76 square feet

Anderson, J.A.; Waters, N.; Richards,L.W. [and others]. 1982. Air

quality sampling during the Green Mountain smoke characterization study. 

[location of publisher unknown]: [publisher unknown]; Report to the 

Environmental Protection Agency; contract TS-AM D-8194.

Byram, G.M. 1959. Forest fire control and use. Davis, K. P., ed. New York: 

McGraw-Hill. 321 p.

Ewing, G.W. 1975. lnstrumented methods of chemical analysis. New York: 

McGraw-Hill.

Sandberg, D.V.; Ward, D.E. [1982]. lncreased wood utilization reduces 

emission from prescribed burning. In: Air quality protection aspects of forestry

management. Tech. Bull. 390. New York: National Council of the Paper 

lndustry for Air and Stream Improvement, Inc.

SCEP. 1970. Man’s impact on the global environment. Cambridge, Mass.: 

MIT Press. 319 p.

Stith, J.L.; Radke, L.F.; Hobbs, P.V. 1981. Particle emissions and the 

production of ozone and nitrogen oxides from the burning of forest slash.

Atmospheric Environment. 7: 73-82.

Ward, D.E.; Core, J.E. 1984. Source emission profiles for Douglas-fir and 

hemlock slash burning. In: Papers, 21st annual meeting of the Air Pollution 

Control Association, Pacific Northwest lnternational Section, 1984 November 

12-14, Portland,OR. Pap. 84-19. Portland,OR: Air Pollution Control 

Association: [not paged].

Ward, D.E.; Hardy, C.C. 1984. Advances in the characterization and 

control of emissions from prescribed fires. In: Papers, 77th annual meeting of 

the Air Pollution Control Association, 1984 June 24-29, San Francisco, CA. 

Pap. 84-36.3. Portland, OR: Air Pollution Control Association: [not paged].

46

Literature Cited
Ward, D.E.; McMahon, C.K.; Johansen, R.W, 1976. An update on 

particulate emissions from forest fires. In: Papers, 69th annual meeting of the 

Air Pollution Control Association, 1976 June 27-July 1, Portland, OR. Pap. 76-

2.2. Portland, OR: Air Pollution Control Association: [not paged].

Ward, D.E.; Sandberg, D.V. 1982. Measurement of smoke from 

prescribed fires in the Pacific Northwest: A progress report. In: Papers, the

Pacific Northwest Air Pollution Control Association Meeting, 1982, Vancouver,

BC. Portland, OR: Air Pollution Control Association: [not paged].

Ward, D.E.; Sandberg, D. V.; Ottmar, R, D. 1982. Measurement of 

smoke from two prescribed fires in the Pacific Northwest. In: Papers, 75th 

annual meeting of the Air Pollution Control Association, 1982 June 20-25, 

New Orleans, LA. Pap. 82-8.4. Portland, OR: Air Pollution Control 

Association: [not paged].

White, W.H. 1981. The role of particulate sulfates and nitrates in reducing 

visibility. In: Papers, 74th annual meeting of the Air Pollution Control 

Association, 1981 June 21-26, Philadelphia, PA. Portland, OR: Air Pollution

Control Association: [not paged].

47
48
49
50
51
52
53
54
55
56
57
58
ASAS active scattering laser probe 

bscat light-scattering coefficient

EAA electrical aerosol analyzer 

FSSP forward scattering spectrometer probe 

EF emission factor

EPA Environmental Protection Agency 

LAS laser aerosol spectrometer 

LEMSCO Lockheed Engineering and Management 

Services Co.

MCI microbalance cascade impactor

MND mean number diameter 

MSL mean sea level 

MVD mean volume diameter

NMHC nonmethane hydrocarbons 

OGC Oregon Graduate Center 

PDT Pacific Daylight Time 

PlXE proton-induced X-ray emission 

PMS particle measuring system 

RTI Research Triangle lnstitute 

S sulfur 

THC total hydrocarbons

TNMHC total nonmethane hydrocarbons

TPV total particle volume 

TSP total suspended particulates 

USDA U.S. Department of Agriculture 

UW University of Washington

59

Abbreviations
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
Radke, Lawrence F.; Lyons, Jamie H.; Hobbs, Peter V.; Hegg, Dean A.; 

Sandberg, David V.; Ward, Darold E. 1990. Airborne monitoring and

smoke characterization of prescribed fires on forest lands in western

Washington and Oregon. Gen. Tech. Rep. PNW-GTR-251. Portland, OR:

U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 81 p.

Detailed airborne measurements of smoke plumes from seven prescribed

burns of forest biomass residues leftover from timber harvests in Washington

and Oregon are described. Measurements of particle size distributions in the

plumes at ≈3.3 km downwind of the burns showed a prominent peak in the

mass concentration for particles ≈0.25-0.30 μm in diameter. The total mass 

of particles in the plume was dominated, however, by supermicron-sized particles. The particle number distributions were dominated by large numbers of

Aitken nuclei (median number diameter ≈0.15 μm).

Based on numerous airborne measurements from six burns, the following

average emission factors were determined using the carbon balance method:

for total suspended particulates 1.2±0.4 percent, for particles <43 μm in 

diameter 0.6I±0.3 percent, and for particles <0.2 μm in diameter 0.4±0.2 

percent. Particle mass fluxes for total suspended particulates, particles <43

μm diameter, and particles <2 μm diameter ranged from 0.1 to 2.4 kg•s-1, 0.1

to 1.1 kg•s-1 and 0.1 to 0.8 kg•s-1, respectively, for the smaller Oregon burns

and from 1.1 to 11.7 kg•s-1, 0.6 to 7.0 kg•s-1, and 0.4 to 14.1 kg•s-1 respectively, for the larger Washington burns.

Other samples collected in conjunction with the airborne work included those

for trace gas analysis, particulate matter for trace element analysis, and gas

concentration measurements for carbon-mass analysis (oxides of nitrogen,

ozone, and hydrocarbons). Mass concentration-to-light scattering coefficient

algorithms and ratios, which can be used to convert integrating nephelometer

response to mass concentration units, are also reported.

Keywords: Emissions, prescribed burning, smoke management.

The Forest Service of the U.S. Department of

Agriculture is dedicated to the principle of multiple

use management of the Nation's forest resources

for sustained yields of wood, water, forage, wildlife,

and recreation. Through forestry research, 

cooperation with the States and private forest 

owners, and management of the National Forests

and National Grasslands, it strives — as directed by

Congress — to provide increasingly greater service

to a growing Nation.

The U.S. Department of Agriculture is an Equal

Opportunity Employer. Applicants for all Department

programs will be given equal consideration without

regard to age, race, color, sex, religion, or national

origin.

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319 S.W. Pine St. 

P.O. Box 3890 

Portland, Oregon 97208
U.S. Department of Agriculture 

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319 S.W. Pine Street 

P.O. Box 3890 

Portland, Oregon 97208

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