Investigate possible causes Intercontinental Transport and Chemical Transformation (ITCT) An International Global Atmospheric Chemistry (IGAC) Program Ozone Trends along U.S. West Coast David Parrish - NOAA Aeronomy Laboratory Goal: Investigate impact of continental emissions on downwind ocean and continents Demonstrate that ozone on U.S. West Coast has increased over last 20 years Today: Discuss some implications

Not a uniquely important region in terms of impact Several studies in North Pacific region over last 2 decades Why focus on Asian Emissions, North Pacific and US West Coast? Asian emissions increased significantly over period of studies - Look for parallel change in ambient levels

Trinidad Head 2002 Cheeka Peak Pt. Arena 1985 Pt. Reyes National Seashore Springtime O 3 Trends Redwood National Park Lassen Volcanic National Park Very few “background” data Caveats: Relatively short records Strongest Asian outflow Focus on Spring Season: Strongest trans-Pacific transport Most studies 2 aircraft studies: NASA CITE 1C in 1984 NOAA ITCT 2K2 in ground sites

(Data selected to avoid North American influence) Conclusion: Along the U.S. west coast, springtime O 3 has increased by ≈ 0.5 ppbv/yr, i.e. ≈10 ppbv in 20 years or ≈1-1.5 %/yr Increasing background ozone during spring on the west coast of North America, Jaffe et al., Geophys. Res. Letters, 30, 2003 Springtime mean O 3 levels have increased

(Select marine air only) Two springtime aircraft studies Same dates, same region Altitude dependence of springtime O 3 increase

(Select marine air only) Conclusion: Increase in O 3 is seen at all altitudes. One indication that it is not strictly local effect. Two springtime aircraft studies Same dates, same region Altitude dependence of springtime O 3 increase

Ozone observations from N.P.S. site at Lassen N.P. (Analysis by Dan Jaffe, University of Washington, Bothell) Seasonal dependence of O 3 increase Conclusion: O 3 increase may be present in all seasons.

Do changes in background O 3 matter? Change in background O 3 Small changes in background O 3 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 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 Local pollution combined with LRT pushed this site over the air quality standard! (Analysis by Dan Jaffe, University of Washington, Bothell)

Atmospheric Photochemistry Primer CH 4 VOC’s CO CO 2 + H 2 O Emission Oxidation of reduced C species 2O 2 O3O3 Absence of NO x destroys O 3 HO 2 OH Radical chain chemistry performs oxidation Production of hydroxyl radical O3O3 O( 1 D) + O 2 O( 1 D) + H 2 O2OH h Presence of NO x catalyzes O 3 production NO 2 NO O3O3 O2O2 h Production of PAN VOC’s + OH …. …. + NO 2 PAN Transports NO x H3CH3C C O O ONO 2

Conclusion: Along the U.S. west coast, springtime PAN has increased by ≈ 3-4 %/yr. Consistent with increasing Asian emissions. Mean Springtime PAN levels have increased Caveat: PAN levels are highly variable and available data are extremely limited (ITCT 2K2 Aircraft data limited to marine boundary layer)

Hydrocarbons and O 3 vary together. Photochemical aging of Asian emissions largely responsible for variations. High northwest winds select for marine boundary layer air. Conclusions from Pt. Arena Study: (Parrish et al., JGR, 97, 15,883, 1992) Pt. Arena Trinidad Head Similar HC variations, but O 3 not nearly as affected.

O 3 levels below 20 to 30 ppbv are much less likely now than in the mid- 1980’s O 3 increase greater at the lower levels

Atmospheric Photochemistry Primer CH 4 VOC’s CO CO 2 + H 2 O Emission Oxidation of reduced C species Production of hydroxyl radical O3O3 O( 1 D) + O 2 O( 1 D) + H 2 O2OH h Photochemical Clock ethane + OH…. propane + OH….  ≈  40 days  ≈  10 days As fresh emissions age, propane/ethane ratio decreases Ratio insensitive to dilution

O 3 dependence on VOC aging In 2002 O 3 was destroyed only slowly as VOC’s aged O 3 (ppbv) In 1985 O 3 was destroyed efficiently as VOC’s aged Conclusion: As Asian NO x emissions have increased, Pacific photochemistry has become less efficient at destroying O 3 (Select marine air only)

Summary: In springtime Impact of Asian Emissions on the Photochemistry of the North Pacific Troposphere Asian emissions have increased by ≈ 5% / year over last 20 years O 3 levels in Eastern Pacific have increased by ≈ % / year PAN levels in Eastern Pacific have increased by ≈ 3-4 % / year Pacific photochemistry has become less efficient sink for O 3 Caveat: Based on very few “background” data of short time span Pt. Arena data are only early PAN and VOC measurements collected over 10 day period

Air Quality Control is beginning to have an international dimension Implication Acknowledgements Ozone Measurements: National Park Service Air Resources Division NASA GTE Data Archive PHOBEA - Jaffe et al. PAN Measurements: NCAR - Ridley et al.; Flocke et al. SRI - Singh et al. PHOBEA - Kotchenruther et al. NOAA - Roberts et al. Hydrocarbon Measurements: NCAR - Atlas et al. SRI - Singh et al.

Propane concentration can substitute. In the past 18 years, O 3 decreases much less strongly with HC aging in spring in the Pacific MBL. Hydrocarbon ratios provide a photo- chemical clock.

Can we find any other data similar to Pt. Arena?ITCT 2002 Aircraft data: ITCT HC MBL samples (< 1 km) Select marine air only Similar to Trinidad Head data

TRACE-P HC DC-8 and P-3 MBL > 25 N aged TRACE-P data: 2000 Further south but also less O 3 dependence

PEM West B HC DC-8 MBL < 25 N aged PEM West B data: 1994 Similar to Pt. Arena, but largely tropical