Ozone Trends along U.S. West Coast
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Ozone Trends along U.S. West Coast David Parrish - NOAA Aeronomy Laboratory. Intercontinental Transport and Chemical Transformation (ITCT) An International Global Atmospheric Chemistry (IGAC) Program. Goal: Investigate impact of continental emissions on downwind

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Investigate possible causes

Ozone Trends along U.S. West Coast

David Parrish - NOAA Aeronomy Laboratory

Intercontinental Transport and Chemical Transformation (ITCT)

An International Global Atmospheric Chemistry (IGAC) Program

Goal: Investigate impact of continental emissions on downwind

ocean and continents

Today:

  • Demonstrate that ozone on U.S. West Coast has increased

    over last 20 years

  • Discuss some implications

  • Investigate possible causes


Investigate possible causes

Why focus on Asian Emissions,

North Pacific and US West

Coast?

  • Several studies in North Pacific

    region over last 2 decades

  • Asian emissions increased

    significantly over period of

    studies - Look for parallel

    change in ambient levels

  • Not a uniquely important region

    in terms of impact


Springtime o 3 trends

Caveats:

  • Very few “background” data

  • Relatively short records

Cheeka

Peak

1997-2002

Springtime O3 Trends

Focus on Spring Season:

  • Strongest Asian outflow

Redwood

National Park

Lassen

Volcanic

National Park

  • Strongest trans-Pacific transport

  • Most studies

Trinidad

Head

2002

6 ground sites

2 aircraft studies:

NASA CITE 1C in 1984

NOAA ITCT 2K2 in 2002

Pt. Arena

1985

Pt. Reyes

NationalSeashore


Investigate possible causes

(Data selected to avoid North American influence)

Springtime mean O3 levels have increased

Increasing background ozone during spring on the west coast of North America,

Jaffe et al., Geophys. Res. Letters, 30, 2003

Conclusion: Along the U.S. west coast, springtime O3 has increased by

≈ 0.5 ppbv/yr, i.e. ≈10 ppbv in 20 years or ≈1-1.5 %/yr


Investigate possible causes

Altitude dependence of springtime O3 increase

  • Two springtime aircraft

    studies

  • Same dates, same region

(Select marine air only)


Investigate possible causes

Altitude dependence of springtime O3 increase

  • Two springtime aircraft

    studies

  • Same dates, same region

Conclusion: Increase in O3

is seen at all altitudes.

One indication that it is

not strictly local effect.

(Select marine air only)


Investigate possible causes

Seasonal dependence of O3 increase

Ozone observations 1988-2001 from N.P.S. site at Lassen N.P.

Conclusion: O3 increase

may be present in all

seasons.

(Analysis by Dan Jaffe, University of Washington, Bothell)


Do changes in background o 3 matter

Do changes in background O3 matter?

Change in background O3

Small changes in background O3 make it harder for us to meet our air quality standard !

(Analysis by Dan Jaffe, University of Washington, Bothell)


Summer 2003 record year for siberian forest fires

Summer 2003: Record year for Siberian forest fires

Aircraft profile on June 2, 2003 found layers of enhanced smoke, carbon monoxide and ozone in these air masses.

Is there a connection with climate change?

(Analysis by Dan Jaffe, University of Washington, Bothell)


June 2003 siberian forest fire impacted seattle air quality june 6 at enumclaw washington

June 2003 Siberian forest fire impacted Seattle air quality June 6 at Enumclaw, Washington

Local pollution combined with LRT pushed this site over the air quality standard!

(Analysis by Dan Jaffe, University of Washington, Bothell)


Investigate possible causes

Emission

Oxidation of

reduced C species

CH4

VOC’s

CO

h

O3

O(1D) + O2

O(1D) + H2O

2OH

Production of hydroxyl radical

CO2 + H2O

OH

NO2

O3

O

2O2

C

H3C

h

O

O

NO2

HO2

NO

O2

O3

Production of PAN

Radical chain chemistry

performs oxidation

VOC’s + OH

….

…. +NO2

PAN

Absence of NOx

destroys O3

Presence of NOx

catalyzes O3

production

Transports NOx

Atmospheric Photochemistry Primer


Investigate possible causes

Mean Springtime PAN levels have increased

Conclusion: Along the U.S.

west coast, springtime

PAN has increased by

≈ 3-4 %/yr.

Consistent with increasing

Asian emissions.

Caveat: PAN levels are

highly variable and

available data are

extremely limited

(ITCT 2K2 Aircraft data limited to marine boundary layer)


Investigate possible causes

Conclusions from Pt. Arena Study:

(Parrish et al., JGR, 97, 15,883, 1992)

Trinidad

Head

  • High northwest winds select for

  • marine boundary layer air.

Similar HC variations, but

O3 not nearly as affected.

  • Hydrocarbons and O3 vary together.

  • Photochemical aging of Asian

  • emissions largely responsible

  • for variations.

Pt. Arena


Investigate possible causes

O3 increase greater at the lower levels

O3 levels below 20 to 30

ppbv are much less likely

now than in the mid-

1980’s


Investigate possible causes

Emission

Oxidation of

reduced C species

CH4

VOC’s

CO

h

O3

O(1D) + O2

O(1D) + H2O

2OH

Production of hydroxyl radical

CO2 + H2O

Photochemical Clock

ethane + OH

….

t ≈40 days

propane + OH

….

t ≈10 days

As fresh emissions age,

propane/ethane ratio decreases

Ratio insensitive to dilution

Atmospheric Photochemistry Primer


Investigate possible causes

Conclusion: As Asian NOx

emissions have increased,

Pacific photochemistry has

become less efficient at

destroying O3

O3 dependence on VOC aging

60

50

  • In 1985 O3 was destroyed

  • efficiently as VOC’s

  • aged

40

30

  • In 2002 O3 was destroyed

  • only slowly as VOC’s

  • aged

O3 (ppbv)

20

(Select marine air only)


Investigate possible causes

Impact of Asian Emissions on the

Photochemistry of the North Pacific Troposphere

Summary: In springtime

  • Asian emissions have increased by ≈ 5% / year over last 20 years

  • O3 levels in Eastern Pacific have increased by ≈ 1-1.5 % / year

  • PAN levels in Eastern Pacific have increased by ≈ 3-4 % / year

  • Pacific photochemistry has become less efficient sink for O3

Caveat: Based on very few “background” data of short time span.

1985 Pt. Arena data are only early PAN and VOC measurements

collected over 10 day period


Investigate possible causes

Implication

Air Quality Control is beginning to have an international dimension

Acknowledgements

Ozone Measurements:

National Park Service Air Resources Division

NASA GTE Data Archive

PHOBEA - Jaffe et al.

PAN Measurements:

Hydrocarbon Measurements:

NCAR - Ridley et al.; Flocke et al.

NCAR - Atlas et al.

SRI - Singh et al.

SRI - Singh et al.

PHOBEA - Kotchenruther et al.

NOAA - Roberts et al.


Investigate possible causes

Propane concentration

can substitute.

In the past 18 years, O3

decreases much less

strongly with HC aging

in spring in the Pacific

MBL.

Hydrocarbon ratios

provide a photo-

chemical clock.


Investigate possible causes

ITCT 2002 Aircraft data:

Similar to Trinidad Head data

ITCT HC MBL

samples

(< 1 km)

Select marine air only

Can we find any other data similar to Pt. Arena?


Investigate possible causes

Further south but also less O3 dependence

TRACE-P data:

2000

TRACE-P HC

DC-8 and P-3

MBL > 25 N

aged


Investigate possible causes

Similar to Pt. Arena, but largely tropical

PEM West B data:

1994

PEM West B HC

DC-8

MBL < 25 N

aged


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