Chemical and Physical Characteristics of

Chemical and Physical Characteristics of Wood Smoke
in the Northeastern US during July 2002 Impacts from
Quebec Forest Fires
Paper # 94, A&WMA Specialty Conference on: Regional and Global Perspectives on
Haze: Causes, Consequences and Controversies, Asheville, NC, October 25-29, 2004.
Richard L. Poirot
Department of Environmental Conservation, Vermont Agency of Natural Resources,
Waterbury, VT 05671-0402
Rudolf B. Husar
Center for Air Pollution Impact and Trend Analysis, Washington University, One
Brookings Drive, Campus Box 1124, St Louis, Missouri 63130

ABSTRACT
During early July 2002, dense smoke from a number of large forest fires in central
Quebec Province was transported south by prevailing winds into the New England and
Mid-Atlantic states. Given the high concentrations of smoke, strong flows from the north,
and relative absence of other emissions in that direction, this event provides a unique
opportunity to evaluate impacts of nearly pure wood smoke at multiple monitoring sites
in the Northeast. Continuous measurements of PM2.5 mass from State and Federal
monitoring programs and light scattering from (a few) IMPROVE nephelometers and
(many) ASOS forward scatter meters reveal highly complex spatial and temporal patterns

of smoke impacts at the surface on July 6-8, 2002. Maximum observed 24-hour smoke
impacts at most US surface sites occurred on July 7th, which was coincidently a routine
filter sampling day for the IMPROVE, STN and FRM (fine mass-only) networks.
Combining the continuous PM, light scattering and filter-based chemical data provides
insights into the chemical and physical features of the smoke during this “event of
opportunity”.
Average 24-hour PM2.5 mass concentrations at heavily impacted sites were almost
entirely limited to the MANE-VU (Mid Atlantic Northeast Visibility Union) region,
ranged from 50 to 150 ug/m3 and reached maximum surface concentrations in the eastern
Mid-Atlantic region. The smoke was composed of 50% organic carbon, an estimated
40% non-carbon organic matter and 4% elemental carbon. Despite the different carbon
analysis methods employed by the IMPROVE and STN networks, organic carbon
measurements were remarkably similar for the two networks, although the elemental
carbon data were not. The ratio of estimated smoke mass to non-soil potassium was
consistent throughout the region and between networks, averaging about 130:1. The
estimated ratio of organic matter to organic carbon was 1.8, the smoke scattering to mass
ratio was 6 m2/g, and the visible light scattering to absorption ratio was 13:1 during
periods of maximum impact. Multi-site receptor modeling identifies a strong, consistent
regional smoke composition, and also reveals regional-scale influences from local
stagnation, transported sulfate and Sahara dust in periods preceding and following the

Quebec smoke.

INTRODUCTION
Recently established US EPA regulations for regional haze have led to expansion of
measurements of fine particle concentration, composition and light extinction in the
IMPROVE network (Interagency Monitoring of PROtected Visual Environments).
Recently promulgated National Ambient Air Quality Standards for PM2.5 have led to a
deployment and expansion of routine monitoring programs for quantifying concentrations
of PM2.5 mass, its spatial and temporal variability and its chemical composition. Recent
deployment of ASOS (Automated Surface Observing Systems) including visibility
sensors (Belfort model 6220 forward scatter meter) at National Weather Service sites also
provides a unique, new, spatially and temporally dense set of haze and aerosol–relevant
data. Growing interest in climate change and associated global radiation budgets have led
to recent deployment of sophisticated satellite and aircraft sensors and surface-based
solar radiation monitors which provide additional perspectives on aerosol concentrations
and optical properties. With support from EPA and Regional Planning Organizations
(RPOs), these many varied forms of haze and aerosol-related data are also becoming
more readily accessible to analysts – for example through Internet-based data distribution
and analysis systems like AIRNOW1, VIEWS (Visibility Information Exchange Web
System)2 and FASTNET (Fast Aerosol Sensing Tools for Natural Event Tracking).3

In July, 2002, many of the above data and information exchange systems were available
in near-real time and led to many quick but detailed assessments of the smoke plume(s)
from a series of large, lightning-induced forest fires which ignited in central Quebec
Province during the first week of July. See for example the various data, images,
animations and analyses reports in the link to “0207 Quebec Smoke” in the FASTNET
Events Catalog.4 Other data, such as from chemical analysis of filters have become
available more slowly. Filter data from the EPA STN network and the IMPROVE
network are especially useful for evaluating the chemical characteristics of the smoke,
since the day of maximum 24-hour smoke impacts at most sites was July, 7th, 2002. This
was a routine 1 in 3 day filter sample day for STN and IMPROVE sites, which are
relatively densely configured in the MANE-VU region of maximum smoke impact. The
location of the fires, as well as regions (north and) south of the fires along the transport
route, are otherwise characterized by very low densities of anthropogenic or other natural
emissions sources. July 7th was a Sunday, assuring day-of-week minima in local
emissions in the region of highest smoke impact. Thus the aerosol concentrations,
compositions and optical effects during this event are largely due to pure wood smoke.
Several aspects of the smoke composition and optical characteristics relate directly to the
concept of “reconstructed extinction” which forms the basis of the EPA Regional Haze
regulations. For example, it is assumed that: organic matter is equal to 1.4 x organic
carbon and has a scattering to mass ratio of 4 m2/g, elemental carbon has an absorption

efficiency of 10 m2/g, and that neither of these species are hygroscopic. The smoke
impacts were also clearly of both “natural” and “extra-jurisdictional” origin, but EPA
guidance for excluding such events from Regional Haze “baseline” or “reasonable
progress” regulatory metrics has not currently been fully developed.

METHODS
Aspects of the wood smoke’s chemical composition were explored with two approaches.
Both began with extraction from VIEWS of all IMPROVE and STN data for the MANEVU region for the summer (July and August) of 2002. In the first approach (“assumption
of overwhelming smoke”), the data were rigorously screened to meet the following
criteria: PM2.5 mass > 50 ug/m3, OC > 25 ug/m3, and sum of all “non-organic species”
(estimated ammonium sulfate + ammonium nitrate + fine soil + EC + all other trace
elements) equal to less than 10% of the mass. For screening purposes, missing nitrate at
a few sites was estimated as the average of nearest sites and sulfur (x3) was substituted
for missing sulfate (or vice versa). The objective was to identify sites with lots of smoke
and almost nothing but smoke. The screening yielded data from 6 IMPROVE sites and
20 STN sites, all on the 7/7/02 sample day of maximum smoke impact. A seventh
IMPROVE site, PMRF, VT, was also added after upward adjustment of the (flagged)
7/7/02 module A data to account for reduced flow observed for that sampler. The
adjustment factor of 1.38 applied to all module A variables was based on the ratio of
IMPROVE fine mass (45 µg/m3) to that from collocated FRM PM2.5 sampler (62 ug/m3).

Following adjustment, a number of QA metrics, including S:SO4, OMH:OMC, OC:MF
and K:OC which had initially been inconsistent were improved to their expected values.
Locations and relative fine mass concentrations of the IMPROVE and STN sites that met
this screening criteria are displayed in Figure 1, which also shows the national spatial
pattern of 7/7/02 fine mass concentrations with FRM PM2.5 data. Here it can be noted
that the influence of “overwhelming smoke” on 7/7/02 was clearly limited to the MANEVU region (shaded light green), and reached highest ground level concentrations in
eastern sections of the Mid-Atlantic states.
Figure 1. Spatial Pattern of US PM2.5 Mass Concentrations on July 7, 2002

Chemical composition of the smoke was also estimated by a second approach (“regional
receptor model”) in which all IMPROVE and STN data from all MANE-VU sites for
July and August, 2002 were entered as independent observations in two runs (one for
each network’s data) of the UNMIX receptor model (version 3.1 for MATLAB).5
Traditionally, this kind of receptor model is applied to large time series of multi-species
data from an individual site, with the objective of identifying specific sources that impact
that site. Similar mathematical approaches – for example “Empirical Orthogonal
Functions” – are also traditionally applied to multi-site data for individual species. In the
current application, a relatively short time series of two months of data from multiple
sites within a small region and intentionally including the large Quebec smoke event, was
employed with the specific objective of identifying the chemical composition of that

event, while also accounting for other regional-scale or more local source influences
which may have been present during that time period. An identified wood smoke source
and any other identified sources that result from this kind of regional application would
need to meet the characteristics of having a fixed, unique chemical composition, and also
having contributions in different samples that were uniquely different from other
identifiable sources, and would need to meet these criteria for multiple sites. Thus the
source influences resulting from this approach must be regionally consistent.
IMPROVE and STN data were prepared for model input as follows. The Washington,
DC IMPROVE site was excluded so that the IMPROVE model run would be exclusively
for rural sites – in contrast with the urban STN sites. Observations for which fine mass,
OC and/or both S and SO4 were missing were eliminated, after which all below-MDL
and negative values were coded as “missing” along with other occasionally “true
missing” minor species. After these prepared data were initially entered into UNMIX, a
limited number of model input values were initially selected, which included fine mass
(for intended use as the “total” and “normalization” variable in the model runs); major
mass-contributing species (S or SO4, NO3, OC, EC); potassium (anticipated to be a
potential wood smoke tracer if the “crustal” K is accounted for in the model), crustal
elements (Si, Al, Fe, Ca, Ti – to assure identification of a clear soil source, and thereby
account for “crustal K”) and Sr (which is frequently below MDL but can be a good
indicator of fireworks, which like wood smoke has a high K and OC content. Other trace

elements, such as Na, Ni, V, Se, As, Pb, Zn, which might help identify “strongly flavored
local” sources at a few sites, were intentionally not used as model input here, since the
objective was to identify sources with common regional-scale influence.
Following the initial selection of these model input variables, an UNMIX subroutine
(UNMISS) was employed to “fill missing data”. The intent here was to maximize the
number of input observations, and also to impute specific values for below-MDL data
(which had been set to “missing”), using the relationships among above-MDL data, rather
than excluding observations or pre-selecting estimated below-MDL concentrations.
Following several preliminary model runs, the UNMIX visual data screening tools (plot
“selected species vs. tracer”) were employed to identify and remove observations with
anomalous outliers – that fell “outside the relational bounds” of most of the data. For the
IMPROVE model runs, the original raw data included 400 samples.

Following the above-described data screening and hole-filling procedures, 358
observations from 18 sites were employed as final model input. For the STN model run,
667 observations (from an original
Figure 2. Locations of MANE-VU Region
753) for 43 sites were employed as
IMPROVE & STN Sites for multi-site Unmix runs.
STN model input. The locations of

the selected sites are displayed in
Figure 2, in which the large symbols
depict the geographical centroids of
the two networks within the MANEVU region. In addition to
differences in sampling and
analytical methods, and in local site
characteristics between the (urban)
STN and (rural) IMPROVE
networks, note that the spatial
distribution of MANE-VU STN sites
is distinctly to the southwest of the
IMPROVE sites in this region.
For the final IMPROVE and STN model runs, fine mass was specified as the “total” and
“normalization” variable (the model objective is to apportion the fine mass, and resulting
source compositions and contributions will be in relation to fine mass concentrations).
The above-indicated input species were used to drive the model, and all other species
were subsequently apportioned among the sources using the UNMIX “fit remaining
species” (MLR regression) option.
Optical characteristics (specifically light scattering) of the Quebec smoke were also
explored using a variety of IMPROVE (Optec NGN2 and NGN3) nephelometer data,

ASOS visibility observations (from Belfort forward scatter instruments), and various
collocated or nearby PM2.5 speciation or continuous mass data. The details of methods
employed are best described in association with specific results to follow, but in general:
IMPROVE NGN2 nephelometer and PM2.5 speciation data for the LYBR, GRGU and
ACAD sites were extracted from VIEWS2; data from an experimental operation of a
(heated, 2.5 um cut) NGN3 nephelometer at ACAD were provided by Air Resource
Specialists6; Continuous fine mass data were obtained from the states of VT, NY, CT,
MA and ME; ASOS “bext” data were obtained from FASTNET3. These ASOS data were
initially archived as hourly visual range averages, truncated at 10 miles or less and binned
into 16 standard bins when visual range was less than 10 miles. Generally, the truncation
was not a problem for the sites and hours of heavy smoke impact – where VR was
consistently below 10 miles. In the current FASTNET version of these data, a bext
calculation is provided using a Koschmeider constant of 3000 (bext = 3000/VR, where VR
is expressed in Km and bext is in Mm-1). Use of 3000 (or less), rather than the “standard”
3900 has been successfully employed in past analyses of airport human observer data.
For several reasons discussed later, a constant of 3900 appears to be a better fit for this
smoke event, and we have recalculated the ASOS bext accordingly.

RESULTS: Smoke Chemical Characteristics
Fine Mass and species compositions for the (20) STN and (7) IMPROVE sites that met

the “overwhelming smoke” screening criteria are displayed in Figure 3, which also
includes several summary statistics for the selected sites for the two networks.
Figure 3. Mass Compositions for MANE-VU Sites Heavily Impacted by Smoke on 7/7/02

The IMPROVE sites are identified by name and State (i.e. BRIG1 NJ is Brigantine New
Jersey), and the STN Sites are identified by AQS site code, for which the first 2 numbers
are the state code (42=PA, 10=DE, 34=NY, 36=NY, 24=MD, 44=RI, 33 = NH and
50=VT). As indicated in Figure 1, the most heavily impacted sites lie in the southeast
corner of the MANE-VU region and decrease toward the north, west and northeast.
Despite network differences in carbon analysis methods, the OC data appear to be
remarkably similar for these heavily impacted IMPROVE and STN sites, with network
averages and standard deviations of OC = 50% + 3% of fine mass in both cases. The EC
data (a small mass fraction for this event) are clearly higher at the IMPROVE sites which
show an average OC:EC ratio of 12 + 2, compared to a ratio of 40 + 18 for the STN sites.
For all sites in both networks a large fraction of the measured mass is unspeciated and
reported in Figure 3 as “other organics”. Given the very high fine mass and OC
concentrations and small proportionate contributions of all other species, including
hygroscopic sulfates and nitrates (expressed here in their assumed fully neutralized
forms), a logical assumption is that the unspeciated mass is composed of non-carbon
organic matter. The traditional organic matter adjustment factor (OMx) of 1.4 is too low

to account for this smoke-dominated fine mass, while a very consistent factor of 1.8 + 0.1

is implied for both networks for this “event of opportunity”. Using this implied OMx of
1.8, the mass of smoke was estimated as EC + 1.8 OC, and this “smoke mass” was
compared to “non-soil potassium”7 (KNON = K – 0.6 FE) to evaluate the consistency of
KNON as a potential quantitative smoke tracer specifically for this event. For this
specific fire and sample day, a fairly consistent smoke:KNON ratio of about 133:1 is
obtained for both IMPROVE and STN sites, and may have some value for estimating
smoke impacts (from this fire or “similar ones”) at less heavily impacted sites or dates.
KNON has generally been used as a qualitative smoke tracer in past analyses, but it can
and does vary among sites and fires, since K is emitted as a function of fuel K content
and fuel consumed, while the carbonaceous matter from a given fire can vary according
to the efficiency of combustion – and so the ratio can vary widely. It has also been
suggested that the smoke: KNON ratio may deteriorate with age, as aerosol K from
biomass may tend to form more slowly and have a smaller size distribution than organic
aerosols.8 Conversely, it might also be expected that secondary organic aerosol formation
would lead to increasing organic concentrations as the smoke ages – perhaps accounting
for the higher concentrations at the more southerly sites in the region. This might also
contribute to the higher OC:EC ratios observed at the STN sites which tend to be located
further south than the IMPROVE sites (Figure 2), and if the aging results in increased
formation of oxygenated organic compounds, the ratio of smoke organic matter to
organic carbon (OMx) might also increase with age.
Figure 4. Smoke Ratios as a Function of Latitude for
Figure 4 displays ratios of OMC:OC
Heavily Impacted STN and IMPROVE Sites on 7/7/02
(OMx), smoke mass:KNON and
OC:EC vs. latitude for the heavily
impacted STN and IMPROVE
sites. With increasing secondary
organic aerosol formation over
time, we might expect all of these
ratios to increase with distance
from the source (as latitude
decreases), but there are no
significant changes with latitude
for any of the ratios. The ratios are
also similar for the STN and
IMPROVE sites, except for
OC:EC, which is consistently
higher for the STN sites. The OC
concentrations appear similar for
the two networks (Figure 2) but the
STN EC levels are consistently
lower than IMPROVE, and its this
methods difference, rather than an effect of aging that accounts for the higher STN
OC:EC ratios, although various effects of aging may well have occurred on preceding
days during transport of the smoke from central Quebec to the Northeast US.

In addition to summary statistics reported in Figure 3, several other metrics can be
calculated from additional data available for the IMPROVE sites. The ratio of PM10 to
PM2.5 averaged 1.0 + 0.1 indicating that all the smoke was fine, and also suggesting
minimal impacts from local (coarse particle) sources on the day of highest smoke impact.
The ratio of OMC:OMH was also 1.0 + 0.1, indicating that these separate estimates of
organic matter were very consistent with each other (as they typically are in this region).
It should be emphasized, however, that this consistency does not necessarily make these
estimates correct. Both are based on common assumptions about the relative fractions of
carbon and hydrogen in organic matter. OMC in this case was calculated with the
traditional 1.4 factor (OMC = 1.4 OC) and OMH was calculated as 13.75(H- S/4). If the
correct OMx factor for this event (or other samples) is 1.8 rather than 1.4, the OMH
calculation would need to be increased to (1.8/1.4 * 13.75 = ) 17.7(H-S/4) to balance.
The multi-site UNMIX analysis, conducted as separate model runs for all STN sites and
all IMPROVE sites in the MANE-VU region for the months of July and August, 2002
yielded 4-source solutions for each network run. Despite differences in the STN and
IMPROVE measurement methods, the modeled “regional source influences” appear
similar for the two networks. The sources are interpreted as representing “wood smoke”,
“dust”, “regional sulfates” (primarily transported) and “mixed urban” (primarily local)
source influences. Average regional time series are displayed in Figure 5, with singlesite results from Addison Pinnacles, NY, where STN and IMPROVE are collocated.
Figure 5. MANE-VU Regional Average UNMIX Source Contributions for Summer 2002,
and Site-Specific Results for Collocated STN and IMPROVE Sites at Addison Pinnacle, NY

It may be noted that on a regional network-wide basis, the average total source (and total
fine mass) concentrations are twice as high for the urban STN network than for the rural
IMPROVE sites. However, the modeled source impacts are quite similar for the
collocated site, indicating that the differences in regional network model results don’t
appear to be driven by differences in the measurement methods for IMPROVE and STN.
Additional details for the network average time series are displayed in Figure 6. Note
that, for all sources except the regional sulfate, the STN and IMPROVE results “fitted” in
magnitude, but are plotted on different Y-Scales. The largest difference in scales (STN =
3X IMPROVE) is for the “mixed urban” source, which is interpreted as resulting
primarily from local stagnation in the MANE-VU region. This difference seems logical
given the predominantly urban nature of the STN sites.
Figure 6. Time Series of Regional STN and IMPROVE Sources for Summer, 2002
Expressed as MANE-VU Regional Averages for Routine 1 in 3 day Samples

For the Smoke source - clearly dominated by the 7/7/02 Quebec fire event, and for the
dust source – also exhibiting an extreme regional spike on the preceding sample day of
7/4/02, the regional average impacts are twice as high for the urban STN sites. As will be
demonstrated later, the 7/4/02 dust spike appears to be associated with a major Sahara
dust transport event, which arrived in the MANE-VU region from the Midwest, where it
exhibited even higher concentrations on the preceding sample day of 7/1/02. By
coincidence, both the Sahara dust and the Quebec smoke reached their highest ground-

level concentrations in the southern half of the MANE-VU domain, where there is a
higher concentration of STN sites (Figure 2), and it is this general regional difference in
network siting characteristics, rather than the urban/rural or measurement methods
differences which account for the average network differences for the distant smoke and
dust sources. It may also be noted that the sulfate source impacts, plotted on the same
scale in Figure 6, track closely except for the 7/19/02 sulfate event which reached much
higher concentrations in southern sections of MANE-VU, and was also a day of high
impacts from local sources.
The modeled source compositions are presented in Figure 7, constrained in this case to
species used as common input to the 2 model runs. It should be emphasized that
“sources” resulting from the UNMIX model are un-named, and characterized only by
their (unique, constant) chemical compositions and (unique, varying) contributions to
each sample used as model input. Source interpretations (names) are dependent on the
subjective judgment of the modelers. Also, in this case, the interpretation that these 2 sets
Figure 7. Compositions (Source Mass Fractions) for Similar Sources Identified in UNMIX
Modeling of Multi-site STN and IMPROVE Data for the MANE-VU Region, Summer, 2002.

of sources – resulting from 2 independent model runs on data from 2 networks with
different sites, site characteristics, sampling and analytical methods – have matching
counterparts in the other model run is also a subjective judgment of the modelers.
As for the time series comparisons in Figure 6, the Figure 7 source compositions are
similar for the independent STN and IMPROVE model runs. The extent to which
differences may be related to the different network’s analytical methods or site
characteristics is unknown, but considering these network differences, the similar time
series and compositions are encouraging. Fractional compositions for most species were
generally more than 2 sigma of their uncertainties for most modeled sources, with the
notable exception of the dust source – for which 2 sigma uncertainties for all species
exceeded the fractional source compositions for both IMPROVE and STN model results.
Both dust sources are substantially enriched in SO4 compared to “pure” crustal material,
and the STN dust is also heavily enriched in
Figure 8. Dust Profiles with "urban excess"
OC, NO3 and EC, compared to IMPROVE.
OC, EC and NO3 removed from STN Dust.
Such enrichment might be due to influence
from re-entrained urban road dust and/or
reactions of urban gaseous pollutants on the
surface of crustal particles. If the “urban
excess” is subtracted from the STN dust
profile, the proportionate mass fractions of the
other species are quite similar to those for the
IMPROVE dust source (Figure 8). For the
Quebec fire-dominated wood smoke source,
the STN source composition shows a
substantially lower EC fraction, consistent
with the Figure 3 composition of heavily impacted sites on 7/7/02 and with the different
definitions of EC in the IMPROVE and STN networks. The IMPROVE regional sulfate
source also shows higher EC content than STN as well as higher (but trace) levels of
several crustal elements. The STN mixed urban source has higher OC and lower SO4 than
its IMPROVE counterpart. Both IMPROVE and
Figure 9. Spatial Patterns of Fine Soil from
STN Dust sources have relatively high Al/Ca
STN & IMPROVE Sites, 6/28/02 - 7/4/02
ratios (>3) and Al/Si ratios (>0.5), and as evident
in the Figure 6 time series, both networks are
impacted by a large, regional-scale dust event on
7/4/02, one sample day prior to the Quebec
smoke. Figure 9 displays 10-day HY-SPLIT back
trajectories starting from the centroids of MANEVU STN and IMPROVE sites on 7/4/02. Also
shown are the spatial patterns of fine soil from all
eastern IMPROVE and STN sites on 6/28, 7/1 and
7/4/02. All of the above features are consistent
with a major intrusion of Sahara dust into the
Northeast on 7/4/02, and the arduous transport
route through the Eastern US may help explain
the excess SO4 associated with the dust.

Figure 10. HY-SPLIT Back Trajectories on Days of Highest Proportionate Contributions for
Modeled Unmix Sources at MANE-VU IMPROVE & STN sites during July & August, 2002.

Figure 10 displays HYSPLIT (version 4.7)9 backward air trajectories for the days of
highest proportionate regional average contributions of the sources resulting from multisite UNMIX runs on IMPROVE and STN data. The trajectories were driven by EDAS
(ETA Data Assimilation System, 80 km grid) meteorological data10 and started at noon
EST at heights of 250, 500 and 750 meters AGL from the centroids of the IMPROVE and
STN sites in the MANE-VU region (see Figure 2). They were run for 72 hours backward,
with the exception of the 7/4/02 dust day, where they were extended back 10 days. It
should be noted that these dust day calculations were truncated at a duration of about 8
days due to exceedance of the southern or eastern limits of the ETA meteorological
domain. The 3-day trajectories for the dates of highest proportionate wood smoke (7/7
and 7/10 for IMPROVE and 7/7 and 8/9 for STN) were also truncated at about 2 days,
due to exceedance of the northern edge of ETA domain. As these smoke trajectories
appear to terminate near (or just beyond the origin of the Quebec fires, just east of James
Bay, a transport time of 2 days (or less) is implied for the smoke, which originated about
500 miles north of the northern edge of the MANE-VU domain and nearly 1000 miles
from the southern edge of the MANE-VU domain where maximum smoke impacts were
observed. The trajectories for the regional sulfate source and the “mixed urban” source
are consistent with the interpretations that these sources tend to be associated with
regional transport and local stagnation, respectively.
Identification of these non-smoke regional sources was not the objective of the regional
UNMIX modeling. Rather, the intent was to derive a regionally consistent chemical
composition or “fingerprint” for summer wood smoke, dominated by the Quebec fire
event, while also accounting for effects of other sources during periods of high smoke

impact. On average, the smoke source accounted for 88% of the modeled fine mass on
7/7/02 across the regional STN and IMPROVE sites, with smoke percentages ranging
from less than 50% to more than 95% at some individual sites on 7/7/02. Including the
less heavily impacted sites and dates and accounting for other source influences provides
an independent means of estimating the smoke composition, for comparison with the
estimate derived by screening the sites to identify “overwhelming smoke” impacts.
Figure 11 compares the TOR thermal
carbon fraction composition (as
percent of total carbon) for the
smoke fingerprint derived from the 7
IMPROVE “overwhelming smoke”
sites on 7/7/02 with the IMPROVE
smoke composition derived from the
2-month, multi-site UNMIX
approach. These fingerprints, which
agree closely with each other are also
compared to their counterparts
derived for the MANE-VU region
for summer 2002 and to the 3-year
2001-03 MANE-VU IMPROVE
regional average (excluding the
Quebec smoke impact days).
Compared to these regional averages
(which presumably also include
influence from other forest fires or
residential wood combustion), the
Quebec smoke has substantially
lower fractions of EC1, EC2, EC3 and OC4, with higher fractions of OC2 and OC3.
OC1 and OP fractions for the smoke are similar to the 2002 summer average but higher
than the 3-year annual mean percentages. The consistency between the UNMIX and
overwhelming smoke estimates adds some confidence to both estimates, while the
differences from other averaging times emphasizes the potential value of the TOR
thermal fractions for other receptor modeling applications for sites with mixtures or wood
smoke and other carbonaceous source impacts.
Figure 11. TOR Carbon Fractions for Heavily Smoke
-Impacted IMPROVE sites on 7/7/02 vs. Smoke from
Regional UNMIX and for Other Averaging Times.

A more detailed profile of the UNMIX smoke composition, including species not used as
model input but subsequently apportioned by regression (UNMIX “Fit Remaining
Species” option) is displayed in Figure 12. Also plotted in this figure is the 7/7/02 filter
composition for the (heavily-smoke-impacted) PMRF, VT IMPROVE site (with ModuleA data adjusted as described previously). Figure 13 also displays an independently
derived wood smoke source profile from a recent Positive Matrix Factorization (PMF)
receptor modeling analysis based on 2001-2003 IMPROVE data for the PMRF, VT site,
reported on by Gao et al. (this conference). The species “New EC1” is adopted from the
Gao et al. (2004) analysis for which OP is subtracted from EC1.

All three estimated wood smoke compositions are strikingly similar, especially
considering the recent PMF analysis was based on 3 years of data for the PMRF, VT site,
but specifically excluded the 7/7/02 sample date as it was observed to represent an
“extreme anomaly” which adversely affected the preliminary PMF results. The Regional
UNMIX included that 7/7/02 PMRF VT sample as input, but only as one of 358
observations from other dates and sites in the region.
Figure 12. Wood Smoke Compositions from PMF Modeling of 2000-2003 IMPROVE Data from
PMRF, VT (Gao et al., 2004, which excluded 7/7/02), PMRF, VT composition on 7/7/02, and Smoke
Composition from Regional UNMIX Modeling of Summer 02 MANE-VU Region IMPROVE Data.

The similar potassium content of the multi-site UNMIX and single-site PMF smoke
sources (which is similar to KNON, since the Fe content of these sources is more than 20
times lower than K) compares well with the smoke mass:KNON ratio of 132 + 20 to1 for
the previously reported estimates based on the assumption of overwhelming smoke at
selected IMPROVE sites (Figure 3). It may be noted that this ratio is approximately
double that for previous PMF12 and UNMIX13 wood smoke sources (about 60:1) modeled
from 1989-95 IMPROVE measurements at the PMRF site. Unlike the recent Gao et al.
(2004) results, those earlier smoke sources showed strong winter maxima from local
residential wood burning and sugaring operations, which may have accounted for the
lower ratios. The UNMIX IMPROVE wood smoke source has a Smoke:K(non) ratio of
131, an OC Mass fraction of 52%, an implied organic matter conversion factor of OMC =
1.8 OC (to account for the modeled smoke mass) and OC:EC ratio of 13:1 - all of which
are consistent with the composition estimates for the smoke-dominated IMPROVE sites
summarized in Figure 3. The UNMIX STN source had a Smoke:K(non) ratio of 124 (or
127 if K+ ion is used in place of KNON), an OC Mass fraction of 49 %, an implied
organic matter conversion factor of OMC = 1.8 OC , and an OC:EC ratio of 55:1. These
values are also consistent with the smoke composition estimates for the smoke-dominated
STN sites summarized in Figure 3, with the exception that the modeled STN OC:EC ratio
of 55 is higher than the Figure 3 STN ratio of 40 + 18, although it is within the
uncertainty of the earlier estimates. With the exception of the STN EC estimates, the
other metrics are comparable across networks and analysis methods.

RESULTS: Smoke Optical Characteristics
IMPROVE Optec NGN2 ambient nephelometer data (bsp) are available for three smokeimpacted sites in the Northeast during early July 2002. As indicated in Figure 13 (hours
with RH > 95% removed), impacts occurred first at the most southerly and westerly Lye
Brook, VT site and last (and least) at the most northerly and easterly Acadia, ME site.
Only Lye Brook saw large impacts on the 7/7/02 routine IMPROVE filter day, Gt. Gulf,
NH and Acadia were impacted early and late on 7/8/02 respectively, and all 3 sites show
a final, smaller impact late on 7/9 and early on 7/10, with the Acadia impact primarily on
the 7/10 routine filter sample day. The Acadia data are especially informative, due to the
temporary deployment of a collocated Optec NGN3 nephelometer (with heated 2.5 um
inlet) by Air Resource Specialists6. Figure 14 compares the Acadia NGN2 and NGN3
data for the first 15 days of July 2002, with the 7/8 and 7/10 days of smoke impact
identified separately. Relative humidity ranged from 55% to 85% on 7/8 and from 36%
to 91% on 7/10, but the relatively high smoke impacts on these days clearly exhibit no
enhanced effects from humidity. Acadia 24-hour filter-based fine mass concentration on
7/10 was 21 ug/m3, of which 46% was OC, 14% was non-carbonaceous and, as for the
much more heavily impacted sites on 7/7/02, a factor of 1.8 x OC is needed to account
for the measured mass. Since the 7/10 Acadia smoke is clearly not hygroscopic, the best
estimate of its scattering efficiency can be estimated from the NGN3 data, since there is
no need to consider the complex effects of coarse particles or the unknown timing of the
day’s sulfate and nitrate with respect to RH. Reconstructed dry fine particle scattering (in
Mm-1) can be calculated as bsfpd (from NGN3) = 10 (Rayleigh) + 3 x (ammonium sulfate
+ ammonium nitrate) + 1 x (fine soil) + S:MO x (1.8 OC). Solving for S:MO (scattering to
mass ratio for organic matter) yields a scattering to mass ratio of 4 m2/g for organic
matter. This would increase to 5 m2/g if the traditional OMC factor of 1.4 OC were
employed, although 1.8 seems more consistent with the data.
Figure 13. Nephelometer Bsp at 3 Smokeimpacted Northeastern IMPROVE Sites

Figure 14. Bsp (NGN2) vs. Bsfpd (NGN3)
at Acadia NP IMPROVE site.

Figure 15 shows additional details of the data from Acadia and near-by sites, including
ASOS visibility data (forward scatter meter) from the Bar Harbor airport (about 6 miles
NE of the IMPROVE site) and continuous PM 2.5 mass data (TEOM) from Bangor Maine
(about 40 miles to the NW). The ASOS scattering data are initially recorded as 1-minute
averages, and subsequently averaged to 1 hour and converted to visual range (VR). For
archival, they are subsequently truncated at VR = 10 miles with lower visibilities binned
into progressively smaller categories ( 95% RH removed)
with continuous PM2.5 mass measurements from nearby Rutland, VT – about 35 miles
NW. At that time, VT DEC was testing a Mie Data Ram (nephelometer) configured as a
PM2.5 mass monitor in Rutland, collocated with a 30 degree C TEOM. During most of
the summer of 2002, the Data Ram (which internally converts light scattering to
estimated fine mass) tracked the TEOM fairly closely, but during the smoke event its
estimated mass concentration exceeded the TEOM by a factor of 2. It was run in this
case without an internal “adjustment factor”, in which case a dry scattering:mass ratio of
about 3 m2/g is implied. The doubling of estimated fine mass during the smoke impact,
suggests a doubling of the scattering efficiency or about 6 m2/g. A similar efficiency is
also implied if it is assumed that the peak Rutland TEOM PM2.5 mass concentrations
were similar to what was observed in Lye Brook a few hours offset in time.
Figure 17 compares ASOS bscat data from Boston, MA, Hartford, CT, New Haven, CT
and White Plains NY with continuous PM2.5 mass data from nearby sites in these cities.
The 2 independent measurements agree remarkably well during the period of peak smoke
impact, when the ASOS 10-mile data truncation is not a problem, and strongly highlight
the potential value of this dense ASOS network for future analyses. If the raw ASOS
data (prior to truncation, binning and averaging) could be made routinely available, this
value would be greatly extended for analysis of events of less overwhelming magnitude.
Note that the ratio of the scales, by which the bscat data are fitted to the PM2.5 mass, is
consistently 6:1 in all cases, for an implied scattering to mass ratio of 6m2/g.

Figure 17. ASOS bscat vs. nearby PM2.5 in selected Northeastern Cities, July 6-9, 2002.

These very high implied scattering efficiencies are unusual, but are consistent with the
relatively large particle size distributions of this smoke as reported by Taubman et al.
(2004)14 from aircraft sampling in the southern Mid-Atlantic region on July 8, 2002.
They encountered a dense, elevated smoke plume at a height of 2000 to 3000 meters,
where scattering and absorption in the plume centerline exceeded 1000 Mm-1 and 100
Mm-1 respectively and the estimated single scattering albedo was 0.93. They noted with
an optical particle counter (Met One Model 9012) that there were as many particles (by
number) in the range of 0.40 to 0.491 nm as there were in their (smallest) 0.3 to 0.40 nm
size bin, and at several of their flight locations, there were as many particles in the 0.491
to 0.60 nm size range as there were in their smallest bin. Beneath the smoke plume, in a
more typical anthropogenic plume, the smaller 0.3 to 0.4 um particles were much more
numerous than the larger ones.14 The extremely high scattering efficiency implied by the
various surface measurements reported here would require a tight particle size
distribution centered near the most optically efficient 0.5 um size. With an OMC factor of
1.8, smoke scattering of 6 m2/g and EC absorption of 10 m2/g, the single scattering
albedo (scattering / [scattering + absorption]) for the heavily-smoke-impacted IMPROVE
sites would be the same 0.93 (for 550nm) observed in the more sophisticated aircraft
observations reported by Taubman et al. (2004).14

CONCLUSIONS
The unusually large impacts from the July 2002 Quebec forest fires in the Northeastern
US provided a unique “event of opportunity” for exploration of the chemical and physical
properties of nearly pure wood smoke at a large number of routine monitoring sites. The
smoke event was preceded and followed by other large regional-scale impacts from local
sources, mid-range sulfate transport, and very distant transport of a major Sahara Dust
event. During the smoke event, most measurements from the STN and IMPROVE
networks appeared to be quite comparable, with the notable exception of EC. The
organic mass to OC ratio was consistently 1.8 throughout the impacted region. Non-soil
K appeared to be a relatively stable tracer for this specific event, with a smoke:KNON
ratio of about 130:1. The smoke scattering efficiency appeared to increase with smoke
concentration from 4 m2/g at low concentrations to 6 m2/g at heavily impacted sites. EPA
reconstructed extinction formulae would understate the smoke impacts by a factor of 2.

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AKNOWLEDEMENTS
The authors thank Alan Leston, CT DEP, Tom Downs, ME DEP, Dirk Felton, NY DEP,
Peter Babich, VT DEC and George Allen, NESCAUM for providing continuous PM2.5
mass data and Joe Adlhoch, Air Resource Specialists for the Acadia NGN3 data.