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

1. GOME SCIAMACHY10 Emissions11-14 AM3 Model NO2 Observed Model PDF (%) Ozone Anomalies Daily average ozone in 0-8am downslope flow Tropospheric Ozone Trends at Mauna Loa Observatory Tied to Decadal Climate Variability Meiyun Lin1,2 (Meiyun.Lin@noaa.gov), Larry W. Horowitz2, Samuel J. Oltmans3, Arlene M. Fiore4, SongmiaoFan2 Published Online 26 January 2014 http://dx.doi.org/10.1038/ngeo2066 1Atmospheric and Oceanic Sciences, Princeton University and 2NOAA Geophysical Fluid Dynamics Lab, Princeton, NJ3CIRES/University of Colorado and NOAA Earth System Research Lab, Boulder, CO4LDEO/Columbia University, Palisades, NY Rising northern midlatitude baseline O3 in spring when Asian pollution transport is greatest Climate variability modulates tropospheric ozone trends 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 O3at 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. MLO Model East Asian COt 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. NOx emissions in Eastern China almost tripled from 1980s to 2000s Observations [Parrish, D. D. et al., 2012] The puzzle: Mauna Loa ozone increases in fall but shows little change during spring Increasing ozone at MLO inFALL tied to a shift in the PNA towards more frequent positive modes since mid-1990s Sensitive to the subtropical jet location that is modulated by ENSO, Pacific Decadal Oscillation (PDO), and the Hadley circulation Observed (3.4 km altitude) % Change in East Asian COt (1996-2011 minus 1980-1995) A climate perspective on seasonal ozone changes at MLO (Model w/ fixed emissions) Deep in the tropics: The pressure dipoles related to the Pacific-North American (PNA) teleconnection pattern influence pollution transport from midlatitudes (Model w/ varying emissions) • 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 The meteorological shiftnear 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) 500 hPa winds Simulated △O3 (1995-2011 minus 1980-1994) at 675 hPa in the absence of emission changes Daily Pacific-North American (PNA) index Weakening airflow from Asia inSPRING tied to recent La-Niña-like decadal cooling in the eastern equatorial Pacific (possibly combined with tropical expansion?) 1976-1977 climate shift15-16 1998-1999 climate shift16-17 More frequent La Niñas Observed Model More frequent El Niños Temporal correlations between September mean MLO O3 and GPH in the domain PDF (%) NCEP △GPH (Geopotential Height) (1995-2011 minus 1980-1994) at 500 hPa Daily average ozone in 0-8am downslope flow East Asian COt Transport pathway Radon-222 (Bq/m3), a tracer of continental influence Ozone anomalies El Niño Enhanced ridges near Hawaii during the positive PNA, accompanied by a deepening of the Aleutian Low, facilitate isentropic subsidence of midlatitude pollution towards Hawaii. Ozone La Niña The shift from a warm to a cold PDO regime manifests as a decrease in ozone-richEurasianairflowreaching MLO 675hPa • Long-term ozone measurements contain signatures of climate variability! • Decadal climate shiftscan 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 sites3-6may 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 controlsto mitigate the impacts of tropospheric ozone on climate, health, and agriculture AMIP Simulations (Mar-Apr) (Driven by varying SSTs and radiative forcing; with constant O3 precursor emissions) A larger influence from ozone-poor tropical air due to the widening of the tropical belt since 1960s18-21 ? During strong El Niño events, the equatorward shift and eastward extension of the subtropical jet enhances transport of Asian pollution to the eastern North Pacific La Nina events have occurred more frequently since the 1998-1999 Pacific climate shift, leading to weakening airflow from Asia ENSO Neutral (AMIP) Changes in 25th % of daily 675hPa O3 (2000-2012 minus 1960-1975) 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) 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) 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) 10www.temis.nl, base onBoersma, 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]) 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) 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) 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)