# 1992 to 2005 Meteorological Factors Conducive to Ozone Formation in the Portland-Vancouver Area (ODEQ, April 2006)

Anthony Barnack Air Quality Division Oregon Department of Environmental Quality (503) 229-5713

### Abstract Elevated ground level ozone concentrations in the Portland/Vancouver airshed have slightly decreased in the period between 1992 and 2005. In the same period, ozone precursor VOCs and NOx leve ls went down slightly while maximum summer time temperatures rose. Population and vehicle miles traveled also increased. When comparing similar temperature episodes be tween years the ozone levels declined slightly. Temperature episod es are defined as three or more days with maximum temperatures above 90 o F, average wind speeds less than 10 mph, and solar radiation above 1.0 langley/hr.

Introduction: Ozone is a secondary pollutant produced by a mixture of Nitroge n dioxide and Oxygen under strong ultraviolet radiation ( hv ). This reaction is driven by the creation of more Nitrogen dioxide from the reaction of volatile organic carbons under ultraviolet radiation and free radicals (See ozone chemistry followi ng this report). The highest ozone levels occur during the summer months
, during clear, hot days with poor ventilation
Meteorological parameters which affect ozone formation: Temperature: In Portland/Vancouver the ozone levels start to approach Air Quality Index levels of “Unhealthy For Sensitive Groups” and the National Ambient Air Quality Standards (NAAQS) when temperatures are near or above 90oF for three consecutive days or more with poor ventilation.

Ventilation: Ventilation refers to the amount of verti cal mixing in the atmosphere. With good ventilation the dirty ground level air is trans ported up and replaced with cleaner air. In short, good ventilation reduces the ground leve l volatile organic ca rbon levels and the resulting ozone. The rule of thumb is for good ventilation to occur th e average horizontal wind speed should be greater than 10 mph.
Solar radiation (ultraviolet radiation): The time of year is important because the angle of the sun and duration of the day determine the ultraviolet radia tion intensity and duration.
Portland and Vancouver have many programs de signed to lower the emissions of the ozone precursor pollutants of Volatile Organi c Carbon and Nitrogen dioxide. One way to determine the efficacy of these programs is by analyzing the ozone trends while considering the trends for ozone precurso rs, vehicle miles traveled, and population growth. This analysis would not be comple te, however, without accounting for variations in meteorological conditions such as temperat ure and ventilation. These parameters must be considered to place ozone levels in c ontext. Once the meteorological conditions are identified a better comparison of ozone tre nds can be made usi ng ozone episodes with similar weather conditions.

### Results 1. Ozone The NAAQS for ozone is calculated by averag ing three consecutive years of the fourth highest daily eight hour average ozone. Th is level must be below 0.8 ppm or it is a violation. The eight hour ozone standard replaced the one hour standard in 1997 and since that time the Portland/Vancouver Air Quality Maintenance Area has remained in compliance. However, the Portland/Vancouver area has had four exceedances (any eight hour daily max above 0.08 ppm) 1 

### . Figure 1 illustrates the exceedances both before and after the 1997 standard took effect.

0 1 2 3 4 5 6 7 8

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005Number of Exceedance 8hr Ozone Standand Begins



### Figure 1. Portland/Vancouver number of exceedances of eight hour standard 1



### . In Figure 2, the three year average of th e fourth highest maximum daily eight hour average trends down slightly with a slope of -0.001.

y = -0.001x + 0.08

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005Ozone (ppm) Ozone NAAQS > 0.08 8hr Ozone Standand Begins



### Figure 2. Portland/Vancouver three year averag e of fourth highest daily maximum eight hour average. Eight hour st andard begins in 1997.2. Horowitz D., 001_Portland-N ational-DMVT.xls, Portland Metro 3. Population Research Center, College of Urba n and Public Affairs, Portland State University. 4 ODEQ measured VOCs at N. Roselawn, Portland and NOx measured at SE Lafayette, Portland. 

### 2. Vehicle Miles Traveled (VMT) and Population In Figure 3 the Portland/Vancouver VMT 2 

### and Population 3 

### have slopes of +0.08 and +0.04 respectively. The three year average of the fourth highest eight hour average Ozone value has a trend with a slope of -0.002 which is relatively flat.

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005Population (X Million) and VMT (X 10 Million)

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10Ozone (ppm)

VMT(X 10 million) population (mil) 3yr Aver of 4th Highest Ozone Linear (3yr Aver of 4th Highest Ozone)



### Figure 3. 3yr average of 4th highest 8hr average Portland/Vancouver 1979-2004 2,3



### 3. Precursors: The Portland/Vancouver area ozone precursors are Nitrogen dioxide and volatile organic carbons (VOCs). Portland/Vancouver is VOC limited which means that reduction of VOCs reduces ozone levels more effectivel y than a reduction in NOx. TheVOCs that contribute most readily to ozone formation are aldehydes, alkanes, alkenes, and to a lesser extent aromatics. ODEQ has been measuring these compounds in Portland on a consistent basis from 2000 to 2005 (the time of this paper) 4 

### . Figures 4 and 5 contain the May through September average concentratio ns measured by ODEQ in North Portland for Formaldehyde, Acetaldehyde, Propionaldehyde, and Acetone (some of the more common aldehydes). In all cases there is a negative slope as concentrations trend down over the six year period. Formaldehyde levels spiked in 2003 which also had three multiday ≥ 90oF episodes. Acetone levels dropped at a much steeper rate. Maximum Nitrogen dioxide, Nitric oxide, and Nitrogen oxides con centrations have also been declining as shown in Figure 6. Seasonal average Nitrogen dioxide, Nitric oxide, and Nitrogen oxides concentrations have been stable since 1995 with relatively flat slopes (Figure 7).4 ODEQ measured VOCs at N. Roselawn, Portland and measured NOx at SE Lafayette, Portland. y = -0.2x + 2.6 y = -0.09x + 3.8

0 1 2 3 4 5 6

2000 2001 2002 2003 2004 2005ug/m3 Acetaldehyde Formaldehyde Propionaldehyde May - September Averages

y = -0.02x + 0.5



### Figure 4. May through September 2000 to 2005 average Acetaldehyde, Formaldehyde, and Propionaldehyde concentr ations in North Portland 4



### .

y = -0.6x + 3.9

0 1 2 3 4 5 6

2000 2001 2002 2003 2004 2005ug/m3 Acetone May - September Average



### Figure 5

. May through September 2000 to 2005 average Acetone concentrations in North Portland 4



### .4 ODEQ measured VOCs at N. Roselawn, Portland and measured NOx at SE Lafayette, Portland. y = -0.002x + 0.08 y = -0.01x + 0.3 y = -0.02x + 0.4

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.419921993199419951996199719981999200020012002200320042005ppm Max 1hr NO2

Max 1hr NO

Max 1hr NOx



### Figure 6. SE Portland, May through Sept ember 1992 to 2005 maximum one hour average concentrations of Nitrogen di oxide, Nitric oxide, and Nitrogen oxides 4



### .

y = 0.0001x + 0.006 y = -0.0005x + 0.02 y = -0.0009x + 0.03

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.0419921993199419951996199719981999200020012002200320042005ppm Aver 1hr NO2

Aver 1hr NO

Aver 1hr NOx



### Figure 7. SE Portland, May through September 1992 to 2005 Seasonal average concentrations of Nitrogen dioxide , Nitric oxide, and Nitrogen oxides 4



### .5 ODEQ measured temperature at SE Lafayette, Portland. 

### 4. Temperature The Portland/Vancouver temperatures have been trending up from at least 1992 to 2005 as measured by ODEQ at SE Lafayette. The number of days ≥ 90 o F have gone up in the last 14 years as shown in Figure 8. There also have been numerous multi-day episodes of maximum temperatures ≥ 90oF. The years 1993-1996, 1998, 2000, and 2003-2005 all had three plus consecutive day episodes ≥ 90oF. Of these, 1996 and 2003-2005 had the greatest number of consecutive hot days.

1 Day Trendline y = 0.4x + 5.3

2 Day Trendline y = 0.13x + 1.3

3 Day Trendline y = 0.09x + 0.5 0 2 4 6 8 10 12 14 16 18

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005No. of 1, 2, & 3 Days +90F 1 day >90oF

2 Consecutive days >90oF

3 Consecutive days >90oF



### Figure 8. Number of consecutive days ≥ 90oF for one, two, and three day episodes as measured by Oregon DEQ at SE Lafayette 5



### . A break down of the three plus day episodes (F igure 9) reveals the number of three, four, five, and six consecutive day events each year. Of days ≥ 90oF, 1993, 1994, 1996, 2003, and 2004 all had episodes of four days or l onger. 1996 was the worst with the only six day episode and two three day episodes. More recently 2003 and 2004 had three and four day episodes.

0 1 2 3

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 YearNo. of 3, 4, 5, & 6 Days +90F 3 Days in a Row +90o F 4 Days in a Row +90o F 5 Days in a Row +90o F 6 Days in a Row +90o F



### Figure 9. Three, four, five, and si x day episodes of consecutive days ≥ 90oF 5



### .6. Ventilation indices 1977 to 1996 provided by ODEQ 1996 Meteorological Factors Conducive to Ozone Formation in the Portland/Vancouver Area. 7. Ventilation indices 1998 to 2004 provided by Oregon Dept. of Ag. using Salem soundings. 

### 5. Ventilation The ventilation can be represented using th e ventilation index which is calculated by multiplying the wind speed and the mixing height . The mixing height is the elevation below which all ground level mixing occurs. The lower the ventilat ion index the poorer the mixing. The ventilation index for days with the highest one hour ozone values from 1977 to 1996 were presented in the 1996 Meteorological Fact ors Conducive to Ozone Formation in the Portland/Vancouver Area 6 

### . This graph is reproduced in Figure 10 below.

0 5 10 15 20 25 3019771978197919801981198219831984198519861987198819891990199119921993199419951996

yearVentilation Index

0 0.05 0.1 0.15 0.2 0.251 hr max Ozone (ppm) Ventilation Index

max 1hr Ozone



### Figure 10. Ventilation index on the maximum one hour ozone day 1979-1996 6



### . The ventilation index for eight hour average ozone from 1998 to 2004 7 

### is shown in Figure 11. Not surprisingly, the ventilation index is poor for both one hour and eight hour average maximums ozone levels. For reference, the Washington Department of Ecology displays th e ventilation index categories in Table 1 for air sta gnation levels on their web site. http://www.ecy.wa.gov/programs/air/aginfo/M M5Instructions.htm . Jackson County, Oregon uses a ventilation index of level of 400 to ban woodstove burning in winter.6. Ventilation indices 1977 to 1996 provided by ODEQ 1996 Meteorological Factors Conducive to Ozone Formation in the Portland/Vancouver Area. 7. Ventilation indices 1998 to 2004 provided by Oregon Dept. of Ag. using Salem soundings. 0 5 10 15 20 25 30 35 40 45 50

1997 1998 1999 2000 2001 2002 2003 2004 2005 YearVentilation Index

0 0.02 0.04 0.06 0.08 0.1 0.12 0.148hr Ozone Average Ventillation Index Max 8hr



### Figure 11. Ventilation index on th e maximum 8hr ozone day 1998-2004 7



### .

Table 1. Ventilation Index categor ies used for smoke management. Ventilation Index Dispersion 0-50 Very poor 50-2350 Poor 2350-4700 Marginal-Fair > 4700 Good8. Temperature collected by ODEQ at SE Lafayette. 

### 6. Wind Speed The horizontal wind speed impacts the ventilat ion index as well as the location of the ozone plume. The wind speeds for the maximum eight hour ozone for each year were below six miles per hour as shown in Figure 12. A low wind speed is one of the elements for poor ventilation the other being low mixing heights.

0 2 4 6 8 10 12 14

1990 1992 1994 1996 1998 2000 2002 2004 2006Wind Speed mph

0 0.02 0.04 0.06 0.08 0.1 0.12 0.148hr ozone ppm 24 Average WS
Max 8hr Aver. Ozone



### Figure 12. Wind speed on the maximum ei ght hour average ozone day 1992-2005 8



### . 7. High Ozone Episodes A high ozone episode is defined in this report as a period of three or more consecutive days with maximum temperatures ≥ 90oF, daily average wind speeds < 10 mph, and maximum solar radiation > 0.1 Langleys/minutes . Episodes are grouped into weekday or weekend events. The weekday episodes occurs entirely within th e week. The weekend events end on Saturday.
Episode Identifying Method To find episodes, the maximum daily temper atures at ODEQ’s SE Lafayette, Portland site were identified and plotted from May through September. Figure 13 provides an example plot done for 1996 maximum temperatur es. After these high temperature days were identified, the maximum daily eight hour ozone levels at all the Portland and Vancouver WA sites were retrieved. The wind speed, wind direction, solar radiation, and days of the week were also compiled. The dates with average wi nd speeds above 10 mph were removed from consideration. Days occu rring in mid to late September were also not considered because their solar radiation levels were to low. The resulting three consecutive day episodes were compiled in Table 2. These days were grouped into weekday episodes and weekend episodes. One three episode per year was used for comparison between years. The episodes were selected based on similarities in the time of year, solar radiation, thr ee day temperature trend, and low average wind speed.8. Temperature collected by ODEQ at SE Lafayette. 1996 pdx max daily Temp

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 1105/15/85/155/225/296/56/126/196/267/37/107/177/247/318/78/148/218/289/49/119/189/25

DateTemp C



### Figure 13. Maximum daily temperatur es for 1996 in Portland 8



### .9. Ozone measured by ODEQ and Southwest Washington Clean Air Agency, Meteorological data measured at SE Lafayette, Portland. 

### Table 2. Three day ozone episodes with maximum temperatures ≥ 90 o F, average ws <10 mph, average solar radiation > 1 Langley/hr

Date Day SPR O3 max daily 8hr ave MHS/ MSJ O3 max daily 8hr ave SIS O3 max daily 8hr ave WA O3 max daily 8hr ave Max Tem

p max SR Av er WS mp

s aver SR max WS MPS 7/28/9 2 Tuesday 0.051 0.033 0.036 void 87 1.30 6.2 0.47 10.6 7/29/9 2 Wednesd
ay 0.064 0.043 0.051 0.048 91 1.30 7.0 0.46 10.8 7/30/9 2 Thursday 0.082 0.078 0.066 0.097 100 1.30 4.4 0.46 8.1 8/2/93 Monday 0.057 0.047 0.060 0.053 93 1.23 8.0 0.44 13.2 8/3/93 Tuesday 0.047 0.045 0.065 0.041 98 1.23 8.1 0.39 13.9

8/4/93 Wednesd
ay 0.074 0.073 0.072 0.078 97 1.20 3.9 0.42 6.6 9/6/93 Monday 0.058 0.053 0.043 0.043 90 1.03 5.3 0.30 9.7 9/7/93 Tuesday 0.057 0.038 0.062 0.051 89 1.02 4.2 0.32 7.0

9/8/93 Wednesd
ay 0.058 0.051 0.054 0.048 90 1.05 4.2 0.33 6.6 6/28/9 5 Wednesd
ay 0.046 0.046 void 0.050 89 1.28 9.7 0.47 18.7 6/29/9 5 Thursday 0.057 0.053 0.051 0.057 92 1.28 9.7 0.47 17.8 6/30/9 5 Friday 0.083 0.063 0.062 0.069 97 1.29 7.1 0.46 12.1 7/11/9 6 Thursday 0.067 0.054 0.059 0.057 88 1.33 8.2 0.49 14.3 7/12/9 6 Friday 0.074 0.063 0.062 0.067 92 1.35 7.7 0.50 13.2 7/13/9 6 Saturday 0.106 0.085 0.069 0.081 97 1.34 6.6 0.49 11.7

8/7/96 Wednesd
ay 0.051 0.038 0.053 0.048 89 1.27 6.9 0.45 12.1 8/8/96 Thursday 0.073 0.057 0.066 0.067 92 1.26 6.9 0.44 12.3 8/9/96 Friday 0.079 0.061 0.069 0.066 93 1.26 6.7 0.44 12.19. Ozone measured by ODEQ and Southwest Washington Clean Air Agency, Meteorological data measured at SE Lafayette, Portland.

8/22/9 6 Thursday 0.048 0.036 0.040 0.046 89 1.21 6.9 0.40 10.3 8/23/9 6 Friday 0.065 void 0.059 0.056 92 1.18 7.8 0.39 11.9 8/24/9 6 Saturday 0.073 0.063 0.065 0.067 93 1.10 6.0 0.35 10.3 7/26/9 8 Sunday 0.116 0.100 0.073 0.070 98 1.26 3.9 0.43 6.2 7/27/9 8 Monday 0.088 void 0.077 0.078 97 1.27 4.0 0.38 7.7 7/28/9 8 Tuesday 0.098 0.074 0.062 0.075 99 1.25 5.3 0.45 11.7 6/26/0 0 Monday 0.056 0.049 0.054 0.054 91 1.28 7.3 0.48 11.2 6/27/0 0 Tuesday 0.061 0.057 0.066 0.058 96 1.28 5.2 0.47 9.8 6/28/0 0 Wednesd

a 0.067 0.048 0.040 0.045 92 1.29 5.3 0.48 10.2

8/8/01 Wednesd
ay 0.049 0.040 0.047 0.046 86 1.24 8.0 0.43 14.4 8/9/01 Thursday 0.081 0.067 0.055 0.063 96 1.25 4.7 0.43 6.4 8/10/0 1 Friday 0.077 0.066 0.068 0.071 90 1.21 4.6 0.42 7.8 7/22/0 4 Thursday 0.058 0.054 0.058 0.056 98 1.23 7.0 0.44 12.8 7/23/0 4 Friday 0.051 0.051 0.061 0.049 102 1.24 6.5 0.45 9.5 7/24/0 4 Saturday 0.084 0.077 0.058 0.065 100 1.22 6.1 0.44 11.99. Ozone measured by ODEQ and Southwest Washington Clean Air Agency, Meteorological data measured at SE Lafayette, Portland. 

### Three Day Episode Results Figure 14 shows weekday ozone episodes from 1992 to 2005. Figure 15 displays weekend ozone episodes from 1996 and 2004. Ozone on the weekday episodes exhibit a slig ht negative trend with a slope of -0.004. The maximum temperatures for these epis odes dropped more significantly -0.01. This temperature drop only refers to the episode s selected and is not reflective of the temperature trends in Portla nd/Vancouver. The maximum temperatures in the episodes selected were lower toward the end of the 14 year period and could explain in part why the ozone levels in this graph were also lower. The weekend episode data shown in Figure 15 closely track the me teorological parameters.

Trendline y = -0.01x + 1.0 Trendline y = -0.002x + 1.3

Trendline y = 0.004x + 0.5 Trendline y = -0.004x + 0.09

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001SR (Langley), Temp (F)/100, Aver. WS /10

0.02 0.04 0.06 0.08 0.10 0.12 0.14Ozone (ppm)

Max Temp/100 SR Aver WS/10 Ozone max daily 8hr ave


### Figure 14: Three day episodes with maximum temperatures ≥ 90oF, wind speed < 10mph, Solar Radiation >1 Langleys/hr, all weekdays 9



### .9. Ozone measured by ODEQ and Southwest Washington Clean Air Agency, Meteorological data measured at SE Lafayette, Portland. 0.2 0.4 0.6 0.8 1.0 1.2 1.4SR (Langley), Temp (F)/100, Aver. WS /10

0.02 0.04 0.06 0.08 0.10 0.12 0.14Ozone (ppm)

Max Temp/100 SR Aver WS Ozone max daily 8hr ave July 1996 A ug 1996 July 2004



### Figure 15: Three day episodes with maximum temperatures ≥ 90oF, wind speed < 10mph, Solar Radiation >1 Langley /hr with third day on Saturday 9



### . 1998 and 2003 episode comparison. In 2003 there were three multi-day episodes with temperatures ≥ 90 o F but the maximum ozone level only reached 0.084 ppm. Conve rsely, in 1998 there was only one multi-day episode ≥ 90 o F and the maximum level reached 0.116 ppm. If the maximum daily temperature criteria were lowered to ≥ 88oF, there are more episodes to consider.
Three day episodes In 1998 there is one three day episode and in 2003 there are tw o three day episodes ≥ 88oF (Table 2). These episode s all include at least one w eekend day, however, one starts on a Sunday, one ends on Saturday, and one includes both Saturday and Sunday. All three days in the 1998 episode have maximum temperatures in the high 90s and only one day in the 2003 episodes has a temperature in the high 90s. Solar radiation and wind speeds are comparable. Figure 16 compares th ese three episodes. There is a drop in ozone levels in 2003 from 1998, however, the temperature in the 2003 episodes is also lower and the wind speed are higher. The 1998 maximum ozone level occurs on the first day (Sunday) of the three day episode. Th e proceeding day had a maximum temperature of 85oF and a maximum 8 hour ozone of 0.067ppm. The eight hour ozone level had a jump of 0.05 ppm in one day. The first days of the 2003 episode were both only 0.002ppm higher than the proceeding day.9. Ozone measured by ODEQ and Southwest Washington Clean Air Agency, Meteorological data measured at SE Lafayette, Portland. 

### Table 2. Three day ozone episodes with maximum temperatures ≥ 88 o F, average ws <10 mph, average solar radiation > 1 Langley/hr 9

Year Date Day Max O3 Max Temp (X10) max SR aver SR Aver WS mph max WS MPS 7/26/98 Sun 0.116 9.8 1.26 0.43 4 6.2 7/27/98 Mon 0.088 9.7 1.27 0.38 4 7.7 1998
7/28/98 Tue 0.098 9.9 1.25 0.45 5 11.7 6/5/03 Thr 0.070 9.0 1.33 0.50 8 13.7 6/6/03 Fri 0.071 9.6 1.31 0.49 6 10.4 2003 6/7/03 Sat 0.071 9.0 1.29 0.47 5 9.3 6/27/03 Fri 0.046 8.8 1.29 0.48 7 11.8 6/28/03 Sat 0.066 9.2 1.32 0.47 7 13.1 2003 6/29/03 Sun 0.055 8.9 1.29 0.47 9 14.0

0.055 0.066

0.046 0.071 0.071

0.070 0.098

0.088 0.116

0 2 4 6 8 10 12Temp F (X10), WS (mph)

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14Ozone (ppm) Max Temp (X10) Aver WS mph max SR Max O3

Sun - Tues, Jul 26 - Jul 28 Thr - Sat, Jun 5 - Jun 7 Fri - Sun, Jun 27 - Jun 29
1998 2003 2003 

### Figure 16. 1998 and 2003 three day episodes with temperatures ≥ 88oF, ws < 10mph, > 1 Langley/hr 9



### .9. Ozone measured by ODEQ and Southwest Washington Clean Air Agency, Meteorological data measured at SE Lafayette, Portland. 

### Four day episodes Two four day episodes with similar meteor ological patterns occurr ed in 1998 and 2003 in early September (Table 3). The maximum ozone levels during these two four day episodes were virtually identical and they bot h occurred in the second day of the four day stretch (Figure 17).
Table 3. Four day ozone episodes with maximum temperatures ≥ 88 o F, average ws <10 mph, average solar radiation > 1 Langley/hr

Year Date Day Max O3 Max Temp (X10) max SR aver SR Aver WS mph max WS MPS 8/31/98 Mon 0.079 9.6 1.1 0.36 6 9.2

9/1/98 Tue 0.081 9.1 1.1 0.36 5 9.7 9/2/98 Wed 0.041 8.8 1.1 0.36 7 11.2 1998

9/3/98 Thr 0.053 8.9 1.1 0.35 7 11.2 9/2/03 Tue 0.055 9.2 1.0 0.33 5 6.8 9/3/03 Wed 0.084 9.2 1.0 0.30 4 6.6 9/4/03 Thr 0.075 9.2 1.0 0.33 4 6.6 2003

9/5/03 Fri 0.050 9.0 1.1 0.34 4 6.9

1998 vs 2003 Four day episodes

0.081

0.041 0.055 0.084

0.075

0.050 0.079

0.053

0.0 2.0 4.0 6.0 8.0 10.0 12.0Temp F (X10), WS (mph)

0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080 0.090Ozone (ppm) Max Temp (X10) Aver WS mph max SR Max O3

Tue - Thr , Aug 31 - Sept 3 Mon - Wed, Sep 2 -Sept 5
1998 2003 

### Figure 17. 1998 and 2003 four day early Se ptember episodes with temperatures ≥ 88oF, ws < 10mph, > 1 Langley/hr.

### Discussion: In the last 14 years, ozone levels in Portland and Vancouver have been going down slightly while the population a nd the vehicle miles traveled continued to grow. The number of consecutive days with temperatures over 90 o F went up during the same period. When similar high temperature episodes were compared over the years, ozone trends also were slightly negative. Portland also witnessed a drop in precursor pollutants concentrations which helps explain the lowe r than expected ozone levels. The wind speed and ventilation on maximum ozone days were typical for stagnant conditions and were not a factor in the ozone trending.
The 2003 episodes were evidence of this. 2003 had more episodes than a similar hot year, 1998, but had a much lower maximum. The 1998 maximum occurred on a Sunday and jumped 0.05 ppm in one day. This is a ve ry large rate of increase for the eight hour average and indicates that there was much more activity on Sunday than usual along with low wind speeds and high temperatures. The 1998 solar radiation levels were actually lower than the 2003 episodes however. The Monday following this event was a Clean Air Action Day and could have helped lower the precursor pollutants levels. The 2003 episodes had lower ozone levels with simila r meteorological factors which could mean lower precursor levels were present. The pr ecursor trends shown in Figures 4 through 7 above prove this to be true.

Conclusion: The slightly negative ozone trend, the upwar d temperature trends, and the negative precursor trends would indicate that the oz one reduction programs are working. This argument can be made because the Portland/Vancouver population and total vehicle miles traveled continues to grow. However, many of the VOC controls are already in place and Portland/Vancouver could see more ozone with the expected population growth. The Oregon Low Emission Vehicle program is new in 2005-2006 and may result in further reduction in precursors per VMT.

### References 1. Barnack, A. 2004 Oregon Air Quality Data Summaries, Oregon Department of Environmental Quality, Air Quality Division, May 2005. pg 44. 2. Cai, Q. 2004 Oregon Population Report, P opulation Research Center, College of Urban and Public Affairs, Portland State University. Pg 7. 3. Author unknown, 2002 Oregon Population Report, P opulation Research Center, College of Urban and Public Affairs, Portland State University. Pg 6. 4. Turpel M., Principal Transportation Planner 5. Horowitz D., 001_Portland-National-DMVT.xls, Portland Metro 6. Finneran, B. 1996 Meteorological Factors C onducive to Ozone Formation in the Portland/Vancouver Area, Oregon DEQ.
Simplified Ozone Formation Ozone (O 3 

### ) is a secondary pollutant produced by the photolysis of Nitrogen Dioxide (NO 2 

### ) to NO and a single oxygen (O). The single Oxygen (O) bonds to Oxygen (O 2 

### ) in the presence of any solid materi al. In summary the reaction is:

NO 2 

### + O 2 

### + m NO + O 3 

### + m Ozone readily reacts with Nitrogen oxide (NO) to return to oxygen when the ultra violet radiation levels drop.

NO + O 3 

### NO 2 

### + O 2 

### This is an equilibrium which can be driv en to produce more ozone by the addition of more NO 2 

### . NO 2 

### is formed indirectly from the de gradation of volatile organic carbons (RHOC) in the presence of free radicals (OH• ) and ultraviolet radiation. The RHOC and OH• produce another free radical HO 2 

### • which can react with NO to form NO 2 

### and another free radical (OH•).

OH• + RHOC NO + HO 2 

### • NO 2 + 

### OH• nohv hv

hv