Tropospheric Ozone Trends at Mauna Loa Observatory Tied to Decadal Climate Variability

Meiyun LinMeiyun Lin1,2 1,2 (Meiyun.Lin@noaa.govMeiyun.Lin@noaa.gov), Larry W. Horowitz2, Samuel J. Oltmans3, Arlene M. Fiore4, Songmiao Fan2

Rising northern midlatitude baseline O3 in spring when Asian pollution transport is greatest

1Atmospheric and Oceanic Sciences, Princeton University and 2NOAA Geophysical Fluid Dynamics Lab, Princeton, NJ 3CIRES/University of Colorado and NOAA Earth System Research Lab, Boulder, CO 4LDEO/Columbia University, Palisades, NY

The puzzle: Mauna Loa ozone increases in fall but shows little change during spring

The Problem. The response of tropospheric ozone to changing atmospheric circulation is poorly understood but may influence atmospheric composition, climate, health, and agriculture1. Recent studies attribute rising springtime tropospheric O3 at NH remote sites to growth in Asian precursor emissions2-5, but this interpretation conflicts with a Hawaiian ozone record, which increases in fall5-6.

Approach and Key Finding. Analyzing daily to decadal variability in sources of ozone over the subtropical Pacific region using a suite of chemistry-climate model simulations (GFDL AM37-9). Identifying decadal shifts in circulation regimes that modulate ozone-rich airflow from Asia.

So What? Decadal climate shifts must be considered when attributing observed ozone changes to human-induced trends in hemispheric precursor emissions.

Weakening airflow from Asia in SPRINGSPRING tied to recent La-Niña-like decadal cooling in the eastern equatorial Pacific (possibly combined with tropical expansion?)

GOME SCIAMACHY10

Emissions11-14

AM3 Model NO2

Increasing ozone at MLO in FALLFALL tied to a shift in the PNA towards more frequent positive modes since mid-1990s

1Hemispheric Transport of Air Pollution 2010 (UNECE, Geneva, 2010). 2Cooper, O. R. et al., Nature 463, 344-348 (2010)3Parrish, D. D. et al., Atmos. Chem. Phys. 12, 11485-11504 (2012)

7Donner, L. J. et al., J. Clim. 24, 3484-3519 (2011).8Lin, M. et al., J. Geophys. Res.117, D00V07 (2012a)9Lin, M. et al., J. Geophys. Res.117, D00V22 (2012b)

16Meehl, G. A et al., J. Clim. 26, 7298-7310 (2013).17Kosaka, Y. & Xie, S.-P. Nature 501, 403–407 (2013).18Seidel, D. J. et al., Nature Geosci 1, 21-24 (2008)

Temporal correlations between September mean MLO O3 and GPH in the domain

Climate variability modulates tropospheric ozone trends

Long-term ozone measurements contain signatures of climate variability!Long-term ozone measurements contain signatures of climate variability! Decadal climate shifts can offset or augment ozone trends due to changes in global precursor emissions as measured at remote locations. Changes in tropospheric ozone observed at other NH remote sites3-6 may be similarly influenced by climate shifts, though the specific circulation regimes and sources of ozone influencing each location will need to be identified. Identifying the role of climate variability on ozone can help in designing effective emission controls to mitigate the impacts of tropospheric ozone on climate, health, and agriculture

Observed(3.4 km altitude)

(Model w/ varying emissions)

(Model w/ fixed emissions)

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Shifts in atmospheric circulation play a key role in the observed ozone increase in fall and the absence of any change in spring by modulating the Asian pollution reaching MLO.

No change in stratospheric influence

A climate perspective on seasonal ozone

changes at MLO

Sensitive to the subtropical jet location that is modulated by ENSO, Pacific Decadal Oscillation (PDO), and the Hadley circulation

Deep in the tropics:

The pressure dipoles related to the Pacific-North American (PNA) teleconnection pattern influence pollution transport from midlatitudes

500 hPa winds

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Daily average ozone in 0-8am downslope flow

During strong El NiDuring strong El Niñño events, o events, the equatorward shift and the equatorward shift and eastward extension of the eastward extension of the subtropical jet enhances subtropical jet enhances transport of transport of Asian pollutionAsian pollution to the eastern North Pacificto the eastern North Pacific

Ozo

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The meteorological shift near 1995 plays a key role in the observed ozone increase as demonstrated by the model with constant emissions, which captures the abrupt change.

Since the mid-1990s, the daily ozone distribution at MLO shifts towards the high tail (above 50 ppbv)

Daily Pacific-North American (PNA) index

NCEP △GPH (Geopotential Height) (1995-2011 minus 1980-1994) at 500 hPa

Transport pathway

Transport pathway

Enhanced ridges near Hawaii during the positive PNA, accompanied by a deepening of the Aleutian Low, facilitate isentropic subsidence of midlatitude pollution towards Hawaii.

Simulated O△ 3 (1995-2011 minus 1980-1994)at 675 hPa in the absence of emission changes

El Niño

La Niña Ozone

AMIP Simulations (Mar-Apr)(Driven by varying SSTs and radiative forcing; with constant O3 precursor emissions )

ModelObserved

The shift from a warm to a cold PDO regime manifests as a decrease in ozone-rich

Eurasian airflow reaching MLO

More frequent El Niños More frequent La Niñas

1976-1977 climate shift15-16 1998-1999 climate shift16-17

675hPa

Changes in 25th % of daily 675hPa O3 (2000-2012 minus 1960-1975)

ENSO Neutral

(AMIP)

A larger influence from ozone-poor tropical air due to the widening of the tropical belt since 1960s18-21 ?

La Nina events have La Nina events have occurred more frequently occurred more frequently since the 1998-1999 Pacific since the 1998-1999 Pacific climate shiftclimate shift, leading to weakening airflow from Asia

4Logan, J. A. et al., J. Geophys. Res., 117, D09301 (2012)5Oltmans, S. J. et al., Atmos. Environ., 40, 3156-3173 (2006)6Oltmans, S. J. et al, Atmos. Environ. 67, 331-351 (2013)

13van der Werf, G. R. et al., Atmos. Chem. Phys., 10, x (2010)14Schultz, M.G. et al., Global Biogeochemical Cycles, 22, GB2002 (2008)15Chavez, F. P. et al, Science 299, 217-221, doi:10.1126/science.1075880 (2003)

19Lu, J. et al., Geophys. Res. Lett. 36 (2009)20Allen, R. J. et al. Nature 485, 350-354 (2012)21Davis, S. M. & Rosenlof, K. H. J. Clim. 25, 1061-1078 (2012)

10www.temis.nl, base on Boersma, K.F et al., J. Geophys. Res. 109, D04311, 2003

11Lamarque, J.-F., et al., Atmos. Chem. Phys., 10, 7017–7039 (2010)12RCP-8.5 beyond 2005 (Riahi, K. et al., Climatic Change. [2011])

Observations [Parrish, D. D. et al., 2012]

NOx emissions in Eastern China almost tripled from 1980s to 2000s

Model East Asian COt

BUT …BUT …

Ozone at Mauna Loa Observatory (MLO) does not increase in spring despite a spring peak in the Asian pollution influence and tripling emissions from China during the past 30 years.

MLO

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Published Online 26 January 2014 http://dx.doi.org/10.1038/ngeo2066

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Daily average ozone in 0-8am downslope flow