Diurnal and seasonal characteristics
of ozone and PM2.5 in Great Smoky
Mountain National Park, Look Rock, TN
Lee Harden
Environmental Science Program, Appalachian State University, Boone, NC
Abstract
Data obtained from January 2008 to December 2011 in Great Smoky Mountain National Park, Look Rock, TN, by the National Park Service air quality monitoring network,
were used to document overall trends, the diurnal and seasonal characteristics, correlations, and background levels of ozone (O3) and PM 2.5. The overall trend for ozone
and PM2.5 indicated a sinusoidal pattern of rise in the fall from year to year. Wind
speed had an inverse correlation with ozone and PM2.5 concentration. The diurnal
characteristics of ozone and PM2.5 showed little year to year variation, but the summer and spring months exhibited the highest concentrations of both pollutants, while
the fall and winter months exhibited the lowest concentrations of ozone and PM2.5.
Correlation plots confirmed the relationship of high concentrations in spring and summer. Background levels of ozone and PM2.5 both indicated levels of these pollutants
to be relatively constant from 2008-2009 at this site. Overall the transportation and
production patterns of theses pollutants at this site are showing no noticeable rise or
fall in concentration.
1.0 Introduction
Air pollution in national parks is a topic of increasing importance and has drawn the interest
of a wide range of organizations given the link
between air pollution and human and environmental health. Particulate matter, or PM, is the
term for particles found in the air, including dust,
dirt, soot, smoke, and liquid droplets. Major natural sources of PM include terrestrial dust caused
by winds, seaspray, biogenic emissions, volcanic
eruptions, and wild-fires. Although most PM particles tend to be quite large, they have been of
less concern for human health since they tend to
be removed in the upper respiratory system [1].
PM2.5 – particles less than 2.5 micrometers in
diameter – is formed from the reaction of anthropogenic emissions with sunlight. Epidemiological studies (e.g. [2]) have shown a correlation between increased mortality and levels of airborne
particles, particularly PM2.5. Dockery and Pope
(1994) [3] showed a clear relationship between
mortality rates and the concentration of fine particles PM2. 5, as well as with particle sulfate. Fine
particles (PM2.5) are also responsible for most of
the light scattering, or visibility reduction, which
is a concern for park visitors who come to enjoy
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the beautiful scenery and natural landscapes.
Ozone (O3) is another potentially harmful
pollutant when it is present in high concentrations. The Great Smoky Mountain National Park
(GSMNP) has recorded some of the highest levels
of ozone of any national park. At ground level,
ozone is the primary component of smog and
is created when specific pollutants react to the
presence of sunlight. In urban areas, vehicular
and industrial emissions are chief contributors to
ozone production. Ground-level ozone adversely
affects health (e.g. acute respiratory problems
and immune system impairment) and damages
the environment (e.g. plant growth and reproduction rates, agricultural yields, and nutrient
cycling). Ozone has the ability to travel long
distances via metrological transport and can be
deposited over rural areas like GSMNP.
One of the possible mechanisms for long
range transport of ozone from lower altitudes
(Knoxville, TN or Atlanta, GA) to higher altitudes
(GSMNP) is the nocturnal low-level jet (LLJ) [1].
The LLJ is a thin layer of fast moving air (10-20m/
s) located 100 to 200m above the ground [4].
Stull (1988) [4] suggests that the LLJ is capable of
transporting 80-100ppbv ozone over a distance
Journal of Student Research in Environmental Science at Appalachian
of 300km during night hours. We hypothesize
that the LLJ is responsible for the high ozone
concentrations observed in the GSMNP because
there are few local sources for such high levels of
pollutants.
In this study, ozone and PM 2.5 and their
effects on the high elevation environments of
GSMNP Look Rock, TN are examined. Data from
2008 to 2011 were collected from the National
Park Service air quality monitoring network.
The goals of this study are 1) to analyze diurnal
and seasonal variations of ozone and PM 2.5 at
GSMNP Look Rock, TN Monitoring site ; 2) to determine if there are any distinct temporal or seasonal patterns for O3 and PM2.5; 3) to measure
the frequency of ozone and PM 2.5 exceedences
to determine if there is a pattern to their occurrence; 4) to see if there are any correlations between O3, PM2.5, and wind speed ; and 5) to determine the long term trends of O3 and PM2.5 at
GSMNP, Look Rock, TN.
2.0 Site Description
The data sets used for this project span from
January 2008 to December 2011 and were obtained from the National Park Service air quality monitoring station located in GSMNP, Look
Rock, TN (35° 37’ 59”N and 83° 56’ 32”W; elevation 793m) – see Figure 1. GSMNP is surrounded
by a red spruce Frasier fir forest and ~816 square
miles (2113 km2) of national park land. The clos-
est major U.S. interstate (I-140) is ~35km north
north-west from the collection site and the closest maintained highways are ~10km away, one
to the north-east and another to the south-west.
Prevailing winds come from the southwest 10
months out of the year and from the northeast
from September to October [5]. Note that these
conditions would not facilitate direct contamination of the site by vehicular emissions.
The National Park Service air quality monitoring station measures ozone (parts per billion by
volume, ppbv ) using a UV-absorption analyzer,
a weather station including wind speed (m/s),
wind direction, air temperature (OC), solar radiance (W/m2), and relative humidity. The measurements are taken on a continuous year-round
basis with a time resolution of 1 min. The data
used in this analysis was taken from January 1,
2008 to December 31, 2011.
3.0 Methods
The high-resolution (1 minute) time series of
ozone, PM 2.5, solar radiation, and wind speed
at the GSMNP site were plotted. The ozone and
PM2.5 time series were analyzed to determine
whether they were increasing or decreasing over
time and to determine if there were any patterns
or relations to wind speed and solar radiation.
Minute-resolution ozone and PM 2.5 data were
averaged over each of the four years (2008-2011)
and plotted to determine the average diurnal
Figure 1. Map of the Great Smokey Mountain National Park with the Look Rock monitoring station
location marked in yellow. Adapted from Google Earth.
Volume 3, 1st Edition • Spring/Fall 2013
19
characteristics of ozone and PM2.5 over the
study period. The same minute-resolution data
were also averaged over each of the seasons of
the four-year study period and plotted. Seasonal
delineation was based on the standard calendar year seasonal definition (e.g. March 20 and
September 23, 2011 marked the beginning of
the spring and fall seasons in 2011, respectively).
Yearly and seasonally-averaged wind rose plots
were constructed to aid in determining whether
there was a directional dependence for ozone
and PM2.5 (not reported). Additionally, the
number of O3 and PM2.5 exceedances – events
in which levels exceeded EPA levels of “Public
Health Concern” – were recorded to determine if
the number of exceedences where increasing or
decreasing over time.
The U.S. Environmental Protection Agency
(EPA) and the State of North Carolina established
exceedance threshold for tropospheric ozone at
80 ppbv (parts per billion by volume) sustained
for at least an 8-hour period, above which levels
are potentially unhealthy. The EPA’s outgoing
PM2.5 exceedance threshold (1997-2012) was
15 μg/m3 (yearly averaged measurements), and
is 12 μg/m3 (yearly averaged measurements) as
of Dec. 2011; the 24-hour PM2.5 limit is 35 μg/m3
(daily averaged measurements).
Seasonal correlation plots for ozone and
PM2.5 were plotted to determine how ozone and
PM2.5 were related over the seasons. Lastly, the
lowest quartile of ozone and PM2.5 levels were
analyzed to determine if background ozone and
PM2.5 levels were increasing or decreasing over
time. The lowest quartile values of ozone and
PM2.5 are assumed to represent background levels free of significant pollution.
3.0 Results and Discussion
3.1 Time Series Results of Ozone and PM2.5
The complete time series of ozone, PM2.5, solar
radiation, and wind speed over the 2008-2011
study periods is illustrated in Figure 2. The mean
ozone concentration over this period of time was
44.2ppbv (represented by the red line on Figure
Figure 2. O3 (A), PM2.5 (B), and solar radiation (C), and wind speed (D) plots for Great Smokey Mountain
National Park Look Rock, TN.
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Journal of Student Research in Environmental Science at Appalachian
2-A (top)). The blue line on Figure 2-A represents
the EPA standard for troposhperic ozone of 80
ppbv. The EPA standard was exceeded 82 times
in 2008, 69 times in 2009, 81 times in 2010, and
83 times in 2011. The number of exceedances
has been generally constant every year except
2009 where there were only 69 exceedences
above 75 ppbv.
The mean PM2.5 concentrations over the
2008-2011 study period were 11.1 ug/m3 (red
line in Figure 2-B). The EPA standards for PM2.5
concentration are 12ug/m3 for primary (healthbased standard – not indicted on Figure 2-B),
15ug/m3 for secondary (welfare-based standard
– blue line on Figure 2-B), and 35ug/m3 for both
primary and secondary (green line on Figure
2-B). As shown in Figure 2, the primary PM2.5
level (12ug/m3) was exceeded 146 times in 2008,
127 times in 2009, 102 times in 2010, and 121
times in 2011. The secondary PM2.5 level (15ug/
m3) was exceeded 91 times in 2008, 77 times in
2009, 70 times in 2009, and 78 times in 2011. The
35ug/m3 concentration threshold was exceeded
5 times in 2008, 0 times in 2009, 1 time in 2010,
and 1 time in 2011.
The yearly mean concentrations of ozone and
PM2.5 are shown in Table 1. The ozone, PM2.5,
solar radiation (see Figure 2-C), and wind speed
plots (see Figure 2-D) exhibit a sinusoidal pattern
commensurate with seasonal changes. All of the
peaks and troughs occur at relatively the same
time of year except for wind speed, which shows
troughs where there are peaks in ozone, PM2.5,
and solar radiation, indicating that ozone and
PM2.5 concentrations are at their greatest when
wind speed is lowest. When wind speed is higher,
the atmospheric pollutants get dispersed over a
larger area and the concentration of pollutants
decreases.
Table 1: Concentrations of ozone [ppbv] and
PM2.5 [ug/m3], averaged per year from 20082011.
Year
Mean Ozone
Cocnetration [ppbv]
Mean PM2.5
Concentration [ppbv]
2008
44.3
12.0
2009
40.1
10.1
2010
45.9
11.0
2011
46.3
11.2
Volume 3, 1st Edition • Spring/Fall 2013
3.2 Diurnal Results of Ozone and PM2.5
The concentrations of ozone and PM2.5 at each
of the 24 hours per day readings were averaged
yearly from 2008-2011, resulting in a yearlymean diurnal cycle (see Figure 3). Ozone varies
consistently throughout the day for each of the
four years (Figure 3 – top panel). The diurnal
ozone showed a decrease in production from
12am to 10am, and an increase from 10am to
9pm with a peak at 3pm, which illustrates the
photochemical production process of ozone.
The yearly means of PM2.5 (Figure 3 – bottom
panel) mimic the variations of ozone.
The greatest drop in ozone and PM2.5 concentrations occurred from 2008 to 2009 where
the mean went from 44.3ppbv to 40.1ppbv and
12.0 ug/m3 to 10.1ug/m3, respectively (see Table
1).
3.3 Diurnal Seasonal Characteristics of O3
and PM2.5
The diurnal cycles of ozone and PM2.5 at GSMNP
Look Rock, TN were seasonally averaged for each
season from 2008-2011 (see Figures 4-7). Overall ozone values were the highest in the spring
(Figure 4-A) and summer (Figure 5-A) with means
of 49.7ppbv and 49.4ppbv respectively. The fall
(Figure 6-A) and winter (Figure 7-A) season had
the lowest concentrations of ozone with means
of 38.7ppbv and 38.6ppbv.
The increase in afternoon ozone concentrations is likely due to photochemical ozone
production. Reduction in evening ozone concentrations may be due to vertical synoptic
transport [6,7,8] in which boundary layer ozone
is transported upward in the troposphere. The
summer trend of ozone from year to year decreased from a mean of 51.63ppbv in 2008 to a
mean of 43.6ppbv in 2009. The lower values for
ozone (and PM2.5) in 2009 could suggest weaker
meridional transport compared to 2008 [6,7,8].
Ozone levels are highest in the spring and summer, which is likely due to mid-boundary layer
mixing where remnant air is mixed downward
during the day, causing higher concentrations
during these seasons [6,7,8].
The average seasonal diurnal cycles of PM2.5
at GSMNP Look Rock, TN, showed that PM2.5
concentrations started off low and peaked in the
afternoon when photochemical production of
PM2.5 is at its highest. The summer mean concentration dropped from 17.3 ug/m3 in 2008 to
13.5 ug/m3 in 2009, similar in behavior to the
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Figure 3. Average Diurnal cycles for O3 and PM2.5 from 2008-2011.
Figure 4. Average Summer diurnal cycles for O3 and PM2.5 from 2008-2011.
Figure 5. Average Fall diurnal cycles for O3 and PM2.5 from 2008-2011.
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Journal of Student Research in Environmental Science at Appalachian
Figure 6. Average Winter diurnal cycles for O3 and PM2.5 from 2008-2011.
Figure 7. Average Spring diurnal cycles for O3 and PM2.5 from 2008-2011.
pattern seen in O3 for the summer of 2008-2009.
From the summer of 2009 to 2010, the PM2.5
concentration increased by ~1.5 ug/m3, indicating little year-to-year variability.
The highest levels for PM2.5 are observed
during the summer and spring months. This
mimics the seasonal variation of ozone and indicates stronger photochemical production
and transport during these seasons. None of
the diurnal average concentrations were above
the concentrations set by the EPA for PM2.5
(primary=12ug/m3, secondary=15ug/m3, and
combined=35ug/m3).
3.4 Seasonal Correlations between O3 and
PM2.5
Correlations of ozone with PM2.5 for the differVolume 3, 1st Edition • Spring/Fall 2013
ent seasons are shown in Figure 8. The spring
correlation plot shown in Figure 8-A shows a
positive relationship between ozone and PM2.5.
The spring and summer seasons exhibited the
strongest correlation between ozone and PM2.5
– the spring correlation plot had a linear fit of y
= 0.1386x + 5.205 while the summer correlation
plot (Figure 8-B) had a linear fit of y = 0.2355x +
3.470. The fall and winter also showed positive
relationships between ozone and PM2.5, but
the correlation was not as strong as it was for
the summer and spring seasons. The linear fit for
the fall shown in Figure 8-C was y = 0.1249x +
3.510 and for winter shown in Figure 8-D was y =
0.1228x + 3.650. The linear fits for these seasons
are very similar, indicating that the production
and transport patterns of ozone and PM2.5 dur23
Figure 8. Ozone and PM2.5 seasonal correlations.
ing these months has little variation.
3.5 O3 and PM2.5 background levels
In order to discover whether the background
ozone and PM2.5 levels were increasing or decreasing over the period of this study, the lowest quartile of both pollutants were plotted. The
linear fit for the lowest quartile of ozone (Figure
9, top panel) was y = 0.0606x + 35.45, which
indicates a small background year-to-year increase in ozone production or transport. In 2008,
the greatest number of points above the linear
regression line compare to the other years. The
linear fit for the lowest quartile of PM2.5 (Figure
9, bottom panel) was y = 0.0013x + 7.620. Background PM2.5 levels increased negligibly yearto-year from 2008-2011.
4.0 Summary
The atmospheric conditions of PM2.5 and ozone
at GSMNP Look Rock, TN, from 2008-2011 are
generally stable and show little year-to-year variation over this time period. The overall trends for
ozone, PM2.5, solar radiation, and wind speed
were analyzed to determine the broad characteristics of these pollutants at this site. A positive
relationship between ozone, PM2.5, and solar
radiation was observed. Wind speed had a negative relationship with pollutant concentrations.
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Aside from the drop in ozone and PM2.5 mean
concentrations from 2008-2009, no other significant variations in either ozone or PM2.5 were
observed. Seasonal average diurnal profiles for
ozone and PM2.5 showed summer and spring
months had the highest production and transportation rates for both ozone and PM2.5, while
fall and winter months experienced the least
variation in production of ozone and PM2.5.
Seasonal correlation plots between ozone and
PM2.5 showed a positive correlation for all seasons, but the strongest correlations were seen
in summer and spring. Background ozone and
PM2.5 levels, determined by analyzing the
monthly average lowest quartile concentrations
for ozone and PM2.5 from 2008-2011, exhibited
only a minimal increase from 2008-2011.
The ozone and PM2.5 concentrations at the
Look Rock, TN site in the Great Smoky Mountain
National Park were generally steady from 20082011, although this area has experienced some
of the highest number of ozone exceedences of
any national park in the United States.
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Journal of Student Research in Environmental Science at Appalachian
Figure 9. Background ozone and PM2.5 represented by the lowest quartile of the range of data from
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