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Volume 11, issue 7
Atmos. Chem. Phys., 11, 3173–3194, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface...

Atmos. Chem. Phys., 11, 3173–3194, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 04 Apr 2011

Research article | 04 Apr 2011

Multi-scale modeling study of the source contributions to near-surface ozone and sulfur oxides levels over California during the ARCTAS-CARB period

M. Huang1, G. R. Carmichael1, S. N. Spak1, B. Adhikary1,2, S. Kulkarni1, Y. Cheng1, C. Wei1, Y. Tang3, A. D'Allura4, P. O. Wennberg5, G. L. Huey6, J. E. Dibb7, J. L. Jimenez8, M. J. Cubison8, A. J. Weinheimer9, A. Kaduwela10, C. Cai10, M. Wong11, R. Bradley Pierce12, J. A. Al-Saadi13, D. G. Streets14, and Q. Zhang14 M. Huang et al.
  • 1Center for Global and Regional Environmental Research, University of Iowa, Iowa City, IA, USA
  • 2School of Engineering, Kathmandu University, Dhulikhel, Nepal
  • 3Meso-scale modeling, NOAA/NCEP/EMC, W/NP2, NOAA, Camp Springs, MD, USA
  • 4ARIANET Srl, Milano, Italy
  • 5Department of Environmental Science and Engineering and Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
  • 6School of Earth & Atmospheric Sciences, Geogia Institute of Technology, Atlanta, GA, USA
  • 7Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA
  • 8Department of Chemistry, University of Colorado, Boulder, CO, USA
  • 9NCAR, Boulder, CO, USA
  • 10California Air Resource Board, Sacramento, CA, USA
  • 11Department of Geography, The University of Maryland, College Park, MD, USA
  • 12NOAA/NESDIS, Madison, WI, USA
  • 13NASA Langley Research Center, Hampton, VA, USA
  • 14Argonne National Laboratory, Argonne, IL, USA

Abstract. Chronic high surface ozone (O3) levels and the increasing sulfur oxides (SOx = SO2+SO4) ambient concentrations over South Coast (SC) and other areas of California (CA) are affected by both local emissions and long-range transport. In this paper, multi-scale tracer, full-chemistry and adjoint simulations using the STEM atmospheric chemistry model are conducted to assess the contribution of local emission sourcesto SC O3 and to evaluate the impacts of transported sulfur and local emissions on the SC sulfur budgetduring the ARCTAS-CARB experiment period in 2008. Sensitivity simulations quantify contributions of biogenic and fire emissions to SC O3 levels. California biogenic and fire emissions contribute 3–4 ppb to near-surface O3 over SC, with larger contributions to other regions in CA. During a long-range transport event from Asia starting from 22 June, high SOx levels (up to ~0.7 ppb of SO2 and ~1.3 ppb of SO4) is observed above ~6 km, but they did not affect CA surface air quality. The elevated SOx observed at 1–4 km is estimated to enhance surface SOx over SC by ~0.25 ppb (upper limit) on ~24 June. The near-surface SOx levels over SC during the flight week are attributed mostly to local emissions. Two anthropogenic SOx emission inventories (EIs) from the California Air Resources Board (CARB) and the US Environmental Protection Agency (EPA) are compared and applied in 60 km and 12 km chemical transport simulations, and the results are compared withobservations. The CARB EI shows improvements over the National Emission Inventory (NEI) by EPA, but generally underestimates surface SC SOx by about a factor of two. Adjoint sensitivity analysis indicated that SO2 levels at 00:00 UTC (17:00 local time) at six SC surface sites were influenced by previous day maritime emissions over the ocean, the terrestrial emissions over nearby urban areas, and by transported SO2 from the north through both terrestrial and maritime areas. Overall maritime emissions contribute 10–70% of SO2 and 20–60% fine SO4 on-shore and over the most terrestrial areas, with contributions decreasing with in-land distance from the coast. Maritime emissions also modify the photochemical environment, shifting O3 production over coastal SC to more VOC-limited conditions. These suggest an important role for shipping emission controls in reducing fine particle and O3 concentrations in SC.

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