Urban & Rural Ozone in Urban & Rural Ozone in Southern ArizonaSouthern Arizona

Westar Ozone ConferenceWestar Ozone ConferenceSalt Lake City, UtahSalt Lake City, Utah

March 2004March 2004

Arizona Department of Environmental QualityArizona Department of Environmental Quality

Peter HydePeter Hyde

602 771-7642602 771-7642

OUTLINEOUTLINE

8-hr Phoenix ozone concentrations in Phoenix8-hr Phoenix ozone concentrations in Phoenix

Relationship between urban (Phoenix) and rural Relationship between urban (Phoenix) and rural elevated ozone concentrationselevated ozone concentrations

Diurnal patterns of ozone differ between urban and Diurnal patterns of ozone differ between urban and rural settingsrural settings

Rural ozone: sources and chemistryRural ozone: sources and chemistry

Background concentrations of VOC and NOxBackground concentrations of VOC and NOx

OUTLINE, ContinuedOUTLINE, Continued

ImportanceImportance of rural ozone concentrationsof rural ozone concentrations

ConclusionsConclusions

8-hr Phoenix ozone 8-hr Phoenix ozone concentrations in Phoenixconcentrations in Phoenix

2001 – 2003 averages of the annual 42001 – 2003 averages of the annual 4thth high high values show two sites in violation of the values show two sites in violation of the standardstandard

Concentrations have declined through the Concentrations have declined through the yearsyears

Proposed nonattainment area will include Proposed nonattainment area will include nearly all of metropolitan area and environsnearly all of metropolitan area and environs

0

0.01

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Ozo

ne (

pp

m)

95-97 96-98 97-99 98-00 99-01 00-02

3-Year Average 4th High 8-Hour Ozone24 Phoenix Area Sites, 1995-2002

Relationship between Relationship between urban and rural ozoneurban and rural ozone

Rural 8-hr ozone concentrations, on days with Rural 8-hr ozone concentrations, on days with high urban values, are high urban values, are on averageon average 50 to 65% of 50 to 65% of the urban valuesthe urban values

On a day-by-day basis, this rural % varies widely, On a day-by-day basis, this rural % varies widely, from 40 to 90%.from 40 to 90%.

Why isn’t this rural % more constant?Why isn’t this rural % more constant?

Average 8-hr ozone: 24 max days in Average 8-hr ozone: 24 max days in 96-02: metro PHX vs rural96-02: metro PHX vs rural

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120

urban Palo V Hillside Yuma Casa G Chiricahua

pp

b

Urban & rural components of 24 high Urban & rural components of 24 high 8-hr ozone days (1996- 2002)8-hr ozone days (1996- 2002)

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40

60

80

100

120

35206 35217 35272 35587 35628 35638 35938 36003 36004 36032 36317 36389 36396 36450 36737 36743 36748 36752 37109 37113 37122 37446 37448 37449

ppb urban

rural

Rural fraction of elevated urban 8-hr Rural fraction of elevated urban 8-hr ozone concentrations (24 days)ozone concentrations (24 days)

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0.10

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0.30

0.400.50

0.60

0.70

0.80

0.90

35206 35217 35272 35587 35628 35638 35938 36003 36004 36032 36317 36389 36396 36450 36737 36743 36748 36752 37109 37113 37122 37446 37448 37449

fract

ion

Different rural sites differ in their Different rural sites differ in their fraction of the maximum urban valuefraction of the maximum urban value Background sites do not have equal Background sites do not have equal

concentrationsconcentrations

They tend to cluster together, but They tend to cluster together, but differences among sites average 20 ppb and differences among sites average 20 ppb and are as high as 45 ppbare as high as 45 ppb

8-hr max ozone: PHX vs 5 rural sites8-hr max ozone: PHX vs 5 rural sitesPHX max ordered high to lowPHX max ordered high to low

24 max days in 96 - 0224 max days in 96 - 02Urban vs rural: highest 8-hr ozone 1996-2002

0

20

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100

120

35206 37446 35272 35217 35628 37448 37449 37113 36450 36389 36396 35638 35587 36317 37109 36032 36752 36003 36748 35938 36737 36743 36004 37122

ppb

urban

Palo V

Hillside

Yuma

Chiricahua

Casa G

rural avg

Different diurnal patterns between Different diurnal patterns between urban and ruralurban and rural

Afternoon maxima are similar throughout, Afternoon maxima are similar throughout, but nocturnal minima differbut nocturnal minima differ

Those sites at a high enough elevation to be Those sites at a high enough elevation to be unaffected by surface temperature unaffected by surface temperature inversions have equal ozone concentrations inversions have equal ozone concentrations day and nightday and night

Rural sites with extremely low emission Rural sites with extremely low emission densities, as long as they’re subject to a densities, as long as they’re subject to a surface inversion, have low nocturnal O3surface inversion, have low nocturnal O3

Characteristics of sitesCharacteristics of sites

Supersite: 1100 ft, midtown PhoenixSupersite: 1100 ft, midtown Phoenix Salt R: 1150 ft, east fringe of metro areaSalt R: 1150 ft, east fringe of metro area Florence: 1505 ft, desert small town, 8,000Florence: 1505 ft, desert small town, 8,000 Rye: hamlet, 3200 ft, narrow valleyRye: hamlet, 3200 ft, narrow valley Palo Verde: 880 ft, desert, isolatedPalo Verde: 880 ft, desert, isolated Hillside: 4,200 ft, mountain, isolatedHillside: 4,200 ft, mountain, isolated Mt. Ord: 7128 ft, mountain, isolated Mt. Ord: 7128 ft, mountain, isolated Yuma: 138 ft, valley, town of 50,000Yuma: 138 ft, valley, town of 50,000

Hillside, AZ Ozone SiteHillside, AZ Ozone Site

Diurnal patterns in 1-hr ozoneDiurnal patterns in 1-hr ozoneJuly 1998 averagesJuly 1998 averages

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hour

pp

m

Palo

Hill

Super

Salt R

Rye

Florence

Mt Ord

Yuma

diff = 0.016

urban PHX

eastern fringe of PHX

valley, town of 50,000

valley, 8,000

hamlet, 3200 ft, valley

remote desertremote mountain, 4200 ft

remote mountain, 7200 f t

Diurnal patterns in 8-hr ozoneDiurnal patterns in 8-hr ozoneJuly 1998 averagesJuly 1998 averages

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0.010

0.020

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0.040

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1 3 5 7 9 11 13 15 17 19 21 23

beginning hour

pp

m

Palo

Hill

Super

Salt R

Rye

Florence

Mt Ord

Yuma

Salt River max of 77Palo Verde max of 66

The Origins of Rural OzoneThe Origins of Rural Ozone

– Without transport from urban areasWithout transport from urban areas ¼ is from the stratosphere¼ is from the stratosphere ¾ is from natural tropospheric chemistry¾ is from natural tropospheric chemistry

– Chemistry involvesChemistry involvesmethane & biogenic VOC emissionsmethane & biogenic VOC emissionsNO & NO2NO & NO2formaldehydeformaldehydecarbon monoxidecarbon monoxidehydroxy radicalhydroxy radicalacetic and formic acidsacetic and formic acids

Background concentrations of ozone Background concentrations of ozone precursorsprecursors

VOC: about 25 ppbC, compared with 175 – VOC: about 25 ppbC, compared with 175 – 250 in Phoenix250 in Phoenix

Carbonyls: large sample-to-sample Carbonyls: large sample-to-sample variation at remote background site variation at remote background site (Hillside)(Hillside)

HC (2 to 12 C): much lower than urban, but HC (2 to 12 C): much lower than urban, but not zeronot zero

Rural VOCs are 1/10 of urban, but Rural VOCs are 1/10 of urban, but still 25 ppbCstill 25 ppbC

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ppbC

Super98Super97

Scot96Bank96

Super96JR-96

SR-98UM-98

PV-97PV-98

Average VOC: urban vs rural

urban suburban rural

Oxy compounds have variable Oxy compounds have variable concentrations & are above zeroconcentrations & are above zero

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ppbC

11/16/94 01/21/95 04/15/95 06/14/95 08/13/95 10/12/95 12/05/95

acetal acetoneformald mek

Background NO & NO2 Levels are Background NO & NO2 Levels are Low, but not zeroLow, but not zero

Palo Verde NO & NO2: July-August 1998: average

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0.0010

0.0020

0.0030

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0.0060

0.0070

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pp

m NO

NO2average of 0.0030 ppm for NO2

average of 0.0030 ppm for NO2

average of 0.0008 ppmfor NO

Rural vs Urban NOxRural vs Urban NOx

Diurnal NO & NO2: July-Aug 1998 -- urban vs rural

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NO urban

NO2-urban

NO-PV

NO2-PV

Importance of rural ozoneImportance of rural ozone

Can serve as background for urban O3, but Can serve as background for urban O3, but caution is necessarycaution is necessary

Measurements of rural ozone necessary, perhaps Measurements of rural ozone necessary, perhaps at more than one site.at more than one site.

Understanding of geographical setting is importantUnderstanding of geographical setting is important

Background value determines degree of control Background value determines degree of control necessary to meet standardsnecessary to meet standards

Meeting the standard when Meeting the standard when considering background valuesconsidering background values

The percentage reduction to meet an air The percentage reduction to meet an air quality standard depends on three quality standard depends on three variables:variables:

1.1. The measured maximum (or design value) The measured maximum (or design value) concentrationconcentration

2.2. The value of the standardThe value of the standard

3.3. The value of the background that will be The value of the background that will be unaffected by any emission reductionsunaffected by any emission reductions

Meeting the standard, continuedMeeting the standard, continued

%R = %R = ([O3]max – [O3]std) * 100%([O3]max – [O3]std) * 100% ([O3]max – [O3]bk) ([O3]max – [O3]bk)

WhereWhere [O3]max = maximum or design value[O3]max = maximum or design value [O3]std = 8-hr ozone standard = 84 ppb[O3]std = 8-hr ozone standard = 84 ppb [O3]bk = background ozone value (40 – 80 ppb)[O3]bk = background ozone value (40 – 80 ppb)

Meeting the standard, continuedMeeting the standard, continued

[O3]bk in ppb[O3]bk in ppb

%R: % reduction to meet %R: % reduction to meet the 8-hr O3 standard with the 8-hr O3 standard with [O3]max = 100 ppb[O3]max = 100 ppb

00 16%16%

5050 32%32%

8080 80%80%

ConclusionsConclusions

Elevated concentrations of rural ozone are Elevated concentrations of rural ozone are not well synchronized with elevated urban not well synchronized with elevated urban ozone.ozone.

Rural ozone is strongly influenced by Rural ozone is strongly influenced by mountain-top geography.mountain-top geography.

Rural ozone appears nearly independent of Rural ozone appears nearly independent of the degree of nearby population the degree of nearby population (emissions). (emissions).

Conclusions, continuedConclusions, continued

At the remotest background locations, VOC At the remotest background locations, VOC and NOx are non-zero and measurable.and NOx are non-zero and measurable.

The best background location for The best background location for forecasting, modeling, or understanding forecasting, modeling, or understanding urban ozone would be upwind of the city urban ozone would be upwind of the city and would have a similar diurnal profile as and would have a similar diurnal profile as the urban. the urban.