Analysis of Ozone Concentrations 

Between Select Days During 2005-2006 

and 

Recent Years (2012-2014) 

Using Comparative Weather Conditions 

in the

Memphis Metropolitan Area
Table of Contents

Overview........................................................................................................1

Methodology...................................................................................................3

Water Vapor ...................................................................................................5

Clouds...........................................................................................................5

Wind Direction..................................................................................................7

Wind Speed......................................................................................................8

Other Factors.....................................................................................................9

Results...........................................................................................................10

The Exceptional Outlier-June 27th, 2012...................................................................11

Conclusion......................................................................................................12

Overview: Analysis of Ozone Concentrations Between Select Days During 

2005-2006 and Recent Years (2012-2014) Using Comparative Weather 

Conditions in the Memphis Metropolitan Area

Between the years 2005-2007, the 4 permanent ozone monitors in the Memphis metropolitan 

area (Edmund Orgill Park-Millington, TN; Frayser-Memphis, TN; Marion, AR; and Hernando, 

MS) met or exceeded the current 2008 8-hour ozone National Ambient Air Quality Standard 

(NAAQS) of 76 parts per billion (0.076 ppm) on 99 days. In 2011, a 5th ozone monitor was 

installed (Shelby Farms is the NCOR site-Memphis, TN). Even with an extra monitor, there were 

only a total of 21 days between the years 2012-2014 when the 2008 8-hr ozone NAAQS was 

exceeded(a reduction of 78.8%). Although the 2015 ozone season is ongoing at the time that this 

document is being written(over 70% complete with the peak season waning) with ozone data that 

has not yet been certified, there has only been 1 day all year that has exceeded the 2008 8-hr 

ozone NAAQS. If the 2015 season concludes with only 1 day above the NAAQS, the 3-year total 

of NAAQS exceedance days (days that the Memphis metropolitan area has exceeded the 2008 8-

hr ozone NAAQS) for the Memphis Metropolitan area would be 3, a 97% reduction.

0

5

10

15

20

25

30

35

40

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

(As of

8/25)

Number of Days that Exceeded the 2008 O3 NAAQS 

Memphis Metro Area

Days the 2008

O3 NAAQS

ExceededMemphis

Metro Area

Days Exceeding 76 ppb-2008 O3 

Year

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In addition to the massive reduction in the number of exceedance days, the ozone concentration 

levels have also significantly decreased. The ozone design values (the three-year average of the 

4th highest daily 8-hour ozone maximum per year, which determines whether a monitor is 

violating the NAAQS) during the years 2005 and 2006 were 86 and 87 parts per billion (ppb), 

respectively. The ozone design values in 2013 and 2014 were 78 and 73 ppb, respectively (with a 

design value in late August-2015 of 67 ppb). The design value graph can be found as Figure 1 in 

the Shelby/Crittenden/DeSoto Counties 8-Hour Ozone Design Value of the “SCRRAMP-2015” 

For the 2008 Eight-Hour Ozone National Ambient Air Quality Standard. After further research, 

the disparity between the start of the study (2005) and the end of the study (2014) continues to be 

significant when comparing the top ten daily maximum 8-hr ozone concentrations for each year 

(data table can be found in the appendix with the graph shown below). Note that the 10th-highest 

ozone concentrations from both 2005 and 2006 were still greater than the strongest ozone 

concentrations in both 2013 and 2014.

The incredible difference between the number of ozone exceedances between the first few years 

of the comparative study and the last few years (The study mainly concentrated on the years 

2005-2006 and 2012-2014) as well as the significant decrease in ozone concentrations during the 

period led to the hypothesis that weather alone could not be the driving factor in these vast ozone 

reductions during this 10-year period. It was believed that for the most part, a known lower 

emissions inventory played a larger role in ozone reduction than weather conditions during the 

period of 2005-2014 (and is continuing to occur from the initial data that is being compiled for 

2015), but needed further study.

60

65

70

75

80

85

90

95

100

105

110

1 2 3 4 5 6 7 8 9 10

2005

2006

2013

2014

Top Ten Daily Max 8-HR Ozone Conc.-Memphis Metro 2005-06 & 2013-14 Ozone Concentration (ppb)

Rank

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Methodology

In order to test the hypothesis, the 8-highest ozone concentrations (8-hour daily maximum ozone 

concentrations from the Memphis Metropolitan Area ozone monitors) were chosen from 2005 

and 2006 (4-highest concentrations from each year) and compared to days with similar weather 

conditions during the years 2012-2014. Each of these 8 days would have been labeled a “Code 

Red” for ozone under the current 2008 8-hr ozone NAAQS. Once an acceptable number of 

comparative days were compiled and analyzed, ozone values from each of the selected days 

could then be compared to determine if there might be another source of strong influence to the 

ozone development (or lack thereof), such as emission inventory. Each of the 8 days from 2005 

and 2006 were compared to 9-15 days from 2012-2014 with acceptably equivalent weather 

observations from the same surface station (Memphis International Airport). The acceptability 

criteria will be explained later in the Methodology section.

For the last several years, the Shelby County Health Department has been collecting weather 

conditions at the Memphis International Airport (KMEM) in addition to the daily maximum 8-

hour ozone concentrations for each monitor in the metropolitan area. The weather parameters 

were initially collected in order to improve forecasting techniques, but have since proven to be 

useful for other means, as well. The example below shows the complete set of collected weather 

parameters.

A B C D E F G H I J K L M N O P Q R S T U V

6/27/2013 61 59 67 58 57 67 97 76 74 21 51 111 12-7p SCT-W6 

(TS/RA/SQ later) 9.88F 5 C 98/74 46 110

This example has been compacted in order to fit within the document. The headers were also 

removed due to space restrictions. The numbers under letters B-F indicate the 8-hr maximum 

ozone concentrations (in parts per billion) for the day and are color coded to the AQI with the 

monitor with the maximum concentration in the area for the day in bold type. 

A=Date

B=Edmund Orgill Park ozone monitor-Millington, TN

C=Frayser ozone monitor-Memphis, TN

D=Shelby Farms ozone monitor-Memphis, TN

E=Marion, AR ozone monitor

F=Hernando, MS ozone monitor

G=Maximum 8-hr ozone concentration (ppb) for the Memphis area on the given day

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H=Maximum daily temperature-°F (all weather data observed at Memphis International Airport, 

unless otherwise stated)

I=Dew Point (°F) at the time of the max temperature (at times it must be the best meteorological 

estimate, as max temperatures often are recorded between hourly observations)

J=Minimum Daily Temperature (°F)

K=Dew Point Depression at the time of the max temp (difference between Max Temp and Dew 

Point)

L=Relative Humidity at the time of the max temp (%)

M=Heat Index-°F at the time of the max temp (only recorded if 95° or higher)

N=Hours of maximum ozone concentration at the high monitor (The 12:00 hour in 12-7 reflects 

the ozone observed from 11 am-12pm)

O=Labeled WX (weather) comments, but lists cloud cover, wind speed, wind direction, and any 

other pertinent information at the time of the max temp (in this case a thunderstorm, rain, and 

squall line pushed through the area later after the high temperature was recorded)

P=Barometric Sea Level Pressure (SLP) equivalent at the airport during the max temp (in inches) 

as well as the pressure trend (in this case, the SLP was 29.88 inches and falling)

Q=Daily Rainfall amount using GFS MOS categories (0=No rain or trace, 1=0.01-0.09 inches, 

2=0.10-0.24 inches, 3=0.25-0.49 inches, 4=0.50-0.99 inches, 5=1.00-1.99 inches, 6=2.00 inches 

or more)

R=Shows if a front or trough passed through the area on the given day and if so, the type

(C=cold front, W=warm front, S=stationary front, T=trough, and Trop=tropical system)

S=Shows if a front or trough passed through the area on the previous day (if there is no passage, 

the space will be left blank)

T=West Memphis, AR airport weather observation station (WMEM) Max Temp/Dew Point

U=WMEM Relative Humidity (%) at the time of the WMEM max temp

V=WMEM Heat Index (°F) at the time of the WMEM max temp

Although this surface data is extensive, only six weather parameters were used in the comparison 

between the selected days. They were Max Temp (H); Dew Point Depression (K); Relative 

Humidity (L); Cloud Cover (which was expanded to include cloud heights in the study); Wind 

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Direction; and Wind Speed (clouds, wind direction, and wind speed all fall within the O 

column). The Max Temp, Dew Point Depression, and Relative Humidity parameters were 

compared during the hour when the maximum temperature was recorded. The Cloud Cover (as 

well as Cloud Height), Wind Direction, and Wind Speed parameters were averaged over an 8-

hour period (11am-6pm CDT) using the National Climatic Data Center database and then 

compared for the selected days. The Cloud Cover, Cloud Height, and Wind Direction parameters 

were each given a weighted value in order to quantify the comparison. The points given to each 

of these variables is called the Weather Relevance Score (WRS) and is explained in detail below.

Water Vapor

As exact temperature comparisons were not as much of a concern as the Dew Point Depression 

or Relative Humidity, a 3-degree cushion was allowed between the high historical day (2005-

2006) and each of the days between 2012-2014. If the temperature difference exceeded the 3-

degree cushion, a 0.25 point per degree was given to the day with the higher temperature. For 

example, if day 1 recorded a max temp of 100 degrees and day 2 recorded a max temp of 94 

degrees, day 1 would be given a temperature score of 0.75. This would then be added to the other 

variables for a final WRS score.

After many years of study, it has been determined that water vapor plays a major role in the 

development of ozone in the Memphis area. As such, the water vapor score was divided into 

Dew Point Depression (the difference between temperature and dew point) and Relative 

Humidity. Although in many instances, the two parameters coincide in relation to the WRS, it 

was not always the case. Both variables were important to the outcome of the WRS. For each 

degree of difference in the Dew Point Depression variable, a 0.25 point was given to the day 

with the higher Dew Point Depression. A higher Dew Point depression reveals drier air (more 

conducive to ozone development). Similarly, Relative Humidity also shows water vapor in the 

air relative to the temperature. For each percentage point of difference, a 0.25 point was given to 

the day with the lower relative humidity percentage. Both water vapor variable scores were 

added to the WRS.The tables used to score the dew point depression, relative humidity, and 

maximum temperature can be found in Attachment II.

Clouds

After compiling the temperature and water vapor scores (all were scored during the hour of 

maximum temperature), an 8-hour window was used to compare cloud cover (including cloud 

height), wind direction, and wind speed. These variables were then averaged, scored, and added 

to a final WRS score in order to determine if the weather conditions were comparable. If the 

weather scores were deemed comparable, ozone concentrations could then be studied. The 8-

hour window used surface data from Memphis International Airport (gathered from the National 

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Climatic Data Center), the official weather station for Memphis, and averaged observations from 

11am-6pm CDT.

Cloud clover was broken into 5 main categories with 4 sub-categories to fill in the gaps. The 5 

main cloud categories (with initials) are Clear (CLR), Few (FEW), Scattered (SCT), Broken 

(BKN), and Overcast (OVC). Each of these categories used show a percentage of cloud cover 

(estimated for this study) and assigned a value.

CLR=0% cloud cover-fair skies-0 points

FEW=10% cloud cover-mostly sunny skies-1 point

SCT=50% cloud cover-partly cloudy skies-5 points

BKN=80% cloud cover-mostly cloudy skies-8 points

OVC=100% cloud cover-overcast skies-10 points

As the cloud cover can often fall between these categories and cloud heights can also reflect 

thickness (high cirrus clouds are generally not as dense and allow more radiation to reach the 

Earth’s surface), sub-categories were used in order to give the score a little more accuracy. The 

sub-categories are High Overcast (OVC skies over 12,000 feet, but generally between 18,000-

25,000 feet), High Broken (over 12,000 feet), High Scattered (over 12,000 feet), and a subcategory called Few-High Scattered, which was only used when the average score was too high 

for few, but not enough to fall with the high scattered sub-category. There were also occasions 

where an extra point would be added when the cloud heights had mixed cloud-types, such as 

broken at 25,000 feet and scattered at 10,000 feet. The cloud coverage warranted a higher score 

in those circumstances.

The ranges for the cloud categories and sub-categories are as such:

Clear=0.0-0.5 points

Few=0.51-1.74 points

Few-High Scattered=1.75-2.24 points

High Scattered=2.25-4.24 points (High SCT given a value of 3.5 for a 1-hour observation)

Scattered=4.25-5.00 points

High Broken=5.01-6.49 points (High BKN given a value of 5 for a 1-hour observation)

Broken=6.5-8.00 points

High Overcast=8.01-8.99 points (High OVC given a value of 8 for a 1-hour observation)

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Overcast=9-10 points

Once the 8-hour cloud cover total is averaged for each day, it is then given a category or 

subcategory. Each category will then be compared to one another and given a score, which is 

then added to the WRS.

If the categories match, no score is added. 1 category difference (i.e.-CLR to FEW) is equal to 1 

point on the WRS. 2 or more category differences will add 1.5 points for each additional 

category change, as cloud cover can affect solar radiation and play a major role in ozone 

development. For example, if day 1 averages clear skies and day 2 averages broken skies, a 

difference in 3 categories, a 4-point score will be given to day 1 (1+1.5+1.5=4). If the subcategories High SCT, High BKN, and High OVC are involved, the category score would be 

halved. For example, if day 1 averages a High SCT and day 2 averages a SCT, then day 1 would 

be given 0.5 points to add to the WRS, as high SCT is considered to have less cloud cover. If day 

1 averaged a high SCT and day 2 averaged BKN skies, this would be considered a difference of 

one and a half categories and day one would be given 1.75 points for the WRS score (1 category 

would be a full point and the half category would split the difference of a second category 

difference 1.5/2=.75 for a total of 1.75 WRS points). The FEW-High SCT category splits a 

category and a sub-category and then only adds a total of 0.25 WRS points. For example, if day 

1 averages a FEW-High SCT and day 2 averages SCT conditions, then 0.75 WRS points would 

be given to day 1 for a half category plus the 0.25 point bonus.The tables that were used for

scoring and averaging the cloud cover can be found in Attachment II.

Wind Direction

The wind direction variable can determine not only which monitor will most likely be affected, 

but can also play a role in the concentration levels. Although calm winds are usually associated 

with wind speed, if the parcel of air is remaining in one place during favorable hours (late 

morning to early evening), this can help ozone levels increase rapidly and therefore would be 

given added value when quantifying this parameter (will explain in detail below). Variable winds 

tend to be light in nature and can also be associated with increasing ozone concentrations. If 

there are several hours of light and variable winds, ozone levels can increase as the parcel tends 

to remain over an area for an extended period of time. Variable winds have also been given 

added value, although not as great as a calm wind observation. 

In general and depending on wind speed, a forecaster can determine which monitor will see 

higher levels of ozone with an accurate wind direction forecast. Southeasterly winds will 

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generally increase ozone concentrations at the Frayser and Marion monitors. Southerly winds 

can affect the Marion, Frayser, Edmund Orgill Park, and Shelby Farms monitors. Northerly and 

northwesterly winds can affect Hernando monitor. Easterly winds can affect the Marion, Frayser, 

and Shelby Farms monitors. Westerly winds can affect the Shelby Farms monitor. The only 

directional condition that does not affect the area ozone monitors is Northeasterly. This is 

because there are no ozone monitors southwest of the Memphis area (possibly due to sparse 

population in the area). 

The wind direction variable had to be quantified in a way that increased during conditions when 

ozone conditions were more favorable and decreased due to a known factorthat was presentwhen 

ozone levels were lower. On the comparative days, each hourly wind direction observation at 

Memphis International Airport during the 11am-6pm CDT period was given a value. All of the 

directional winds (N, S, E, W, NW, SW, SE, ESE, SSE, SSW WSW, WNW, and NNW) were 

given the value of 1 with the exception of NE and its variations (NNE and ENE). Because the 

ozone values are generally lower on days with a prevalent northeasterly wind, NE was given the 

value of 0.50. NNE and ENE were each given the value of 0.75. Since calm winds are associated 

with increased levels of ozone, a calm observation was given the value of 1.50. Light and 

variable winds are also associated with higher levels of ozone, but not quite as high as calm 

winds, so a variable observation was given the value of 1.25. The 8-hour period was totaled and 

averaged. If one day averaged more than 0.125 than another, it would be given a WRS value of 

0.25 to add to the total score. If one day averaged more than 0.375 in comparison to another, it 

would be given a value of 0.50 to add to the WRS score. For example, day 1 recorded an 8-hour 

(11a-6p) average of 1.22, while day 2 averaged a score of 1, then day 1 would be given a point 

value of 0.25 to add to the WRS score. If neither day has an advantage of over 0.125, then no 

score is given for the wind direction variable for that specific comparison of days.The tables that 

were used for scoring and averaging the wind direction can be found in Attachment II.

Wind Speed

The wind speed variable is very important in the process of ozone development. Winds at the 

surface and aloft not only help to transport ozone and its components, but create atmospheric 

mixing, which causes dilution reducing the amount of ozone (as well as many other pollutants). 

Calm to light winds will not create much atmospheric mixing, which make conditions favorable 

for rapid ozone development. Although winds above the surface are critical to the development 

of ozone, Memphis does not have a definitive way to measure them, as there is no regular 

sounding in the area (weather balloon). The nearest locations that have sounding measurements 

are Little Rock, AR; Jackson, MS; and Nashville, TN. None will be used in this comparison, due 

to distance. We will use the surface winds as a surrogate, since the observation station is relative 

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to the area and the ozone monitors. For instance, calm winds are usually the product of strong 

high pressure at the surface and aloft. Several hours of calm winds during the hours when ozone 

is most likely to develop are indicative of strong ridging. Days that have higher wind speed

averages can still experience ridging, but may also have a pressure gradient building into the 

area. Short wave troughs can also produce higher wind speeds in areas that are under high 

pressure. If an inversion breaks late in the afternoon, wind speeds can increase after being fairly 

dormant for much of the day. 

For this comparison, the 8-hour (11a-6p CDT) wind speed averages were used for the days that 

were being equated. Gusts were incorporated when determining the average by calculating the 

difference in the sustained speed and the gust speed and then dividing by 2, since the full gust 

would not be an accurate indication of the hourly wind speed. The gust would show that there 

was an occasional increase and therefore stronger mixing rates, so it was important to 

incorporate this factor. The total difference in gust and sustained speeds for the 8-hour average 

was calculated, divided by two, and added to the total of sustained speed for a new total and then 

divided by 8 for the average wind speed for the period. For example, if 3 of the hours recorded 

sustained speeds of 8 mph for each hour with gusts of 12, 14, and 16 mph, respectively, the total 

difference between the sustained winds and the gusts would be 18 mph (12-8=4, 14-8=6, 16-8=8, 

thus 4+6+8=18). The number 18 would then be cut in half to 9, which would be added to the 

total of the 8-hour sustained speeds and then divided by 8 for the average of the period.

The days with lighter wind speed averages were rewarded with WRS points. Rounding was used 

when the days were compared. A value of 0.25 was given to the day for each difference in mph 

for the 8-hour average. For example, day 1 averaged 5 mph and day 2 averaged 10 mph. The 

difference of 5 miles per hour would give day 1 a score of 1.25 to use for the WRS.The tables 

that were used for scoring and averaging the wind speed can be found in Attachment II.

Other Factors

Upper-air factors such a pressure, wind speed, and wind directions are very important, but cannot 

be quantified due to a lack of localized measurements. However, archived upper air charts are 

included in the appendix to give a synoptic look at the comparative days. These charts are 

provided to show how the upper air patterns were structured synoptically on the given days.

It should be noted that the 8 days from 2005 and 2006 were compared with days from 2012-2014 

during similar periods. A 3-week time frame was imposed for the comparison in order to 

accurately compare the dates with similar sun angles, solar radiation, and length of day. For 

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example, to accurately compare the 6/23/2005 date, the window of acceptable comparative dates 

would have to come from a period in 2012-2014 from 6/2 to 7/14, 21 days before or after the 

historic date. The 2005-2006 dates as well as the 2012-2014 dates with the comparative scoring

tables, upper air and surface charts, and hourly weather observations from the National Climatic 

Data Center can be found in the appendix.

Reviewing the comparative dates to include in the study was a bit difficult. There were many 

examples of both acceptable and unacceptable weather conditions, but the report needed to be 

revised to a reasonable amount of qualified dates to be both produced and reviewed. Determining 

the threshold for acceptable weather conditions was difficult, but there appeared to be moderate 

differences past the -2.5 mark for the 2012-2014 dates. The positive 2.5+WRS scores showed 

differences as well, but were chosen to remain included in the study. The strong positive WRS 

scores translated to weather conditions that were strongly more favorable than the 2005 and 2006 

dates, but still showed much lower ozone concentrations. Most of the days with strong negative 

numbered days were left out, as they showed low ozone. This would be expectedwith weather 

conditions that were not conducive to ozone development. A score of zero was a match for the 

weather conditions. Scores of 0.0 to 2.50 (or -2.50) were considered a good match. Scores of 

2.75 to 3.50 (-2.75-3.50) were considered fair. A WRS score above (or below) the 3.50 (-3.50) 

mark were not considered as a good or fair match. As stated above however, many of the 

strongly positive scores from 2012-2014 were included because the conditions showed that they 

were much more favorable toward ozone development, but showed lower concentrations than the 

2005-2006 dates.

Results

Once the acceptable comparative dates were compiled, the scores were then matched against

each historic (2005-2006) date within the comparative study. Since the threshold for a good 

Weather Relevance Score (WRS) was 2.5 (or -2.5), it was determined that each WRS point 

would be calculated to equal 4 parts per billion (ppb) of ozone per 1 WRS point. This would 

translate to up to 10 ppb within the good range for weather relevance acceptability and 14 ppb 

for the fair range of acceptability.The WRS for each recent date (2012-2014)of comparison was 

multiplied by 4 with the sum then added (or subtracted) to the ozone concentration of the 

individual historic date of comparison (See the associated tables and graphs in Attachment II).

The results show that for the most part, a significant increase in the 8-hour ozone concentrations 

would have occurred had the ambient air conditions of 2005 and 2006 been matched against the

actual ozone concentrations and weather conditions from the comparative dates in 2012-2014. 

The 2012-2014 dates with the highest levels of ozone experienced weather conditions that were 

far more conducive to very high ozone levels, but were still found to have lower concentrations 

than the historic dates from 2005 and 2006. This strongly suggests that weather did not play a 

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role in the decreased ozone concentrations over the last 8-10 years (See the Results tables and 

graphs in Attachment II).

It is important to note that this study and the results are not intended to be interpreted as exact 

projections, but should be used to illustrate the concept that the weather conditions have not been 

the major factor in the reduction of the number of days that ozone has exceeded the NAAQS as 

well as the reduction in overall ozone concentrations in the Memphis metropolitan area. The 

study and its associated tables and graphs were produced to assist the reader in visualizing the 

vast difference in ozone exceedance days and concentration levels in the last 8-10 years.

The Exceptional Outlier-June 27th, 2012

One date from the most recent few years was left out of the study, as the weather conditions were 

so exceptional, it was determined that it might skew the rest of the comparison. Therefore, it was 

compared to the historic dates on its own. On June 27th, 2012, the Frayser monitor recorded an 8-

hour ozone maximum of 124 ppb-Code Purple (also on that date, Shelby Farms-98 ppb-Code 

Red; Marion-88 ppb-Code Orange; Orgill-80 ppb-Code Orange). The weather conditions on this 

day were incomparable with any other date in recent memory. The max temperature for the day 

was 98 degrees F with a dew point of 47 degrees, a 51-point dew point depression! The relative 

humidity at the time of the max temperature was 18%, which can be likened to near-desert 

conditions. Every sky observation at KMEM during the 8-hour period that was being used in this 

study to determine average cloud cover (11am-6pm) was clear. The 8-hour average wind speed 

was just over 2 MPH with the wind direction score averaging just between the calm and variable 

categories. 

These conditions were due in part to an incredibly strong upper-air ridge that was over the 

middle portion of the country including the Memphis metropolitan area. A very strong surface 

high pressure system over the Southeast U.S. complimented the conditions on 6/27/2012. On the 

previous day as the ridge was over the eastern Great Plains, Houston recorded a Code Purple 

with cities east of Memphis recording Code Red and Code Purple conditions on 6/28/2012. Very 

strong high pressure continued to affect the weather and ozone in the Memphis metropolitan area 

for the next few days with several exceedance days, but nothing close to the conditions that were 

recorded on the 27th. After using HYSPLIT to determine if transport was a factor from the 

Houston area or other cities west of Memphis, it was proven that there was no transport from 

those areas.

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Using the same WRS scoring method to attempt to compare the weather conditions on 6/27/2012 

to the historic high ozone days of 2005 and 2006, it was found that the conditions on the 27th

were profoundly stronger than any of the historic dates. The 2005 and 2006 Weather Relevance 

Scores when compared to the weather conditions on 6/27/2012 were between -8.25 and -18.50! 

See the chart and the graph to see how the WRS scores affected projected ozone levels.

Conclusion

Before the study, it was suspected that factors other than weather were the major force in the 

reduction of days and concentration levels of ozone. Weather patterns had not appeared to 

change drastically and yet Memphis was experiencing incredible reductions in less than a 

decade. Although the 2015 ozone season is waning, but not complete, the monitored data has 

been consistent with a vast reduction in ozone exceedances and concentration levels from the 

2013 and 2014 seasons. The comparison between the 2005-2006 data and the 2012-2014 data 

show similar weather comparisons (with several days in the recent period showing weather 

conditions more conducive to favorable ozone), the 2005-2006 seasons still showed much higher 

levels of ozone. After incorporating the ozone scoring (4 ppb per 1 WRS point), the 2005-2006 

dates projected an average increase of more than 51% compared to the actual ozone data of the 

comparative dates of 2012-2014. This strongly suggests that weather was not the driving factor 

in the reduction of ozone exceedance days and overall concentration levels. Other factors, such 

as significantly reduced emissions in the Memphis metropolitan area (see emissions portion for 

further details) may have played an increased role in the overall air quality improvement for the 

Memphis metropolitan area.

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