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Rapid Increases in Tropospheric Ozone Levels over China: A View from AURA

This article discusses the trends in tropospheric ozone levels over China using satellite observations from the AURA platform. It explores the sources of ozone trends and the impact of Chinese pollution on the western US.

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Rapid Increases in Tropospheric Ozone Levels over China: A View from AURA

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  1. Rapid increases in tropospheric ozone levels over China: The view from AURA Willem W. Verstraeten1, Jessica L. Neu2, Jason E. Williams1, Kevin W. Bowman2, John R. Worden2, K. Folkert Boersma1,3 1. KNMI, the Netherlands; 2. JPL, USA; 3. Wageningen University, the Netherlands A short story about ozone made in China

  2. Trends in tropospheric ozone • O3 increased at many background locations in the 1990s. It continued mainly over Asia and flattened over Europe during the last decade. Situation in North America is mixed. • Relatively long O3 time series are available, but only for few background measurement locations (possible sampling bias). • Satellite observations can bridge the gap thanks to both the good spatial as well as temporal coverage compared to ozone sondes, ground-based instruments, MOZAIC etc. 1.08%/yr Surface O3 Satellite tropospheric O3 China 0.56%/yr W-US Europe IPCC 2012 Asia and North America

  3. What did we do? • Compiling short-term time series of tropospheric O3 satellite observations for eastern China and western United States. • Derive short-term O3 trends over these regions. • Attributing the sources of the observed O3 trends using TM5 constrained with AURA data. • Changes in tropospheric O3 as observed from AURA-TES(Thermal Emission Spectrometer) might be due to • Changes in anthropogenic emissions such as NOX: => AURA-OMI (Ozone Monitoring Instrument); • Variation in the stratospheric contribution to tropospheric O3 => AURA-MLS (Microwave Limb Sounder); • Transport of O3 and its precursors => TM5 (3x2 lon/lat).

  4. TES tropospheric O3 between 2005 and 2010 3-9 km partial O3 column summer 2005-2006 3-9 km partial O3 column summer 2009-2010 DIFFERENCE

  5. OMI tropospheric NO2 between 2005 and 2010 China: +5.4%/yr NO2 column summer 2005-2006 NO2 column summer 2009-2010 Bb W-US: -2.7%/yr DIFFERENCE

  6. Attribution of anthropogenic emissions to tropospheric O3 trends • Constraining TM5 anthropogenic emission inventory using OMI NO2 (mass balance approach, Lamsal et al, 2011). • => Updated NOX emissions for 2005-2010 in TM5 O3 trend explained by changes in anthropogenic NOX emissions Removal of the STE effect! Only effect on NOX update!

  7. Stratosphere-troposphere exchange contributes to tropospheric O3 trends • Stratospheric O3in TM5 is constrained by 30-year (assimilated) 14-satellite dataset of total O3 (van der A. et al., ACP, 2010) • Net stratosphere-troposphere exchange is governed by ECMWF meteo + MSR constraints • STE can be tracked in TM5 with tagged tracer ‘O3S’

  8. Stratosphere-troposphere exchange contributes to tropospheric O3trends • Computed STE trends may be large compared to observations due to the use of ECMWF data (Škerlak et al. 2014, ACP). • MLS observations in the NH only show a small O3 increase in the lower stratosphere (Neu et al., 2014 NGS). • As a lower limit, TM5 STE is constrained by MLS by forcing the model at 200-250 hPa to MLS data. O3 trend explained by changes in STE

  9. The view from AURA: Overview of the sources explaining O3 trends Verstraeten et al. (2015) Nature Geoscience

  10. Asian transport of O3 and precursors towards western US TM5_update – TM5_update_except_China_ref +0.03 DU yr-1 Difference in TM5 runs April-May 2010 O3 at ~800 hPa (±1.5 km) -0.04 DU yr-1 O3 at ~400 hPa (±6 km) Transport from Asia offsets 43% of the local efforts in W-USA!

  11. What about the ozone levels in the lower troposphere near the surface? China W-USA +0.35±0.16 ppbv yr-1 -0.40±0.18 ppbv yr-1 +0.29±0.14 ppbv yr-1 -0.73±0.27 ppbv yr-1

  12. Effect of ozone pollution from China on the W-USA near the surface from TM5 0.05 -------------- x 100 = 6.8% from China 0.73+0.05 0.05 ppbv on 45 ppbv = 0.1% yr-1

  13. Conclusions 2005-2010 tropospheric O3 (3-9 km partial column) over China increased with 1.08% yr-1. OMI NO2 constrains on TM5 increases the ability to reproduce the TES observed O3 trend over China. 56% of the O3 trend over China is explained by anthropogenic sources, and 44% can be attributed to STE. China offsets 43% of the domestic O3 reductions in the western US for 3-9 km partial column. In the lower troposphere near the surface the offset is lower but substantial.

  14. More info: Verstraeten et al., 2015, Nature Geoscience, 8, 690-695

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