Articles | Volume 14, issue 7
Atmos. Chem. Phys., 14, 3657–3690, 2014

Special issue: Observations and modeling of aerosol and cloud properties...

Atmos. Chem. Phys., 14, 3657–3690, 2014

Research article 10 Apr 2014

Research article | 10 Apr 2014

Multi-decadal aerosol variations from 1980 to 2009: a perspective from observations and a global model

M. Chin1, T. Diehl1,2,*, Q. Tan1,2, J. M. Prospero3, R. A. Kahn1, L. A. Remer4, H. Yu1,5, A. M. Sayer1,2, H. Bian1,4, I. V. Geogdzhayev6,7, B. N. Holben1, S. G. Howell8, B. J. Huebert8, N. C. Hsu1, D. Kim1,2, T. L. Kucsera1,2, R. C. Levy1, M. I. Mishchenko6, X. Pan1, P. K. Quinn9, G. L. Schuster10, D. G. Streets11, S. A. Strode1,2, O. Torres1, and X.-P. Zhao12 M. Chin et al.
  • 1NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 2Universities Space Research Association, Columbia, MD, USA
  • 3University of Miami, Miami, FL, USA
  • 4University of Maryland, Baltimore County, Baltimore, MD, USA
  • 5University of Maryland, College Park, College Park, MD, USA
  • 6NASA Goddard Institute for Space Studies, New York, NY, USA
  • 7Columbia University, New York, NY, USA
  • 8University of Hawaii, Honolulu, HI, USA
  • 9NOAA Pacific Marine Environmental Laboratory, Seattle, WA, USA
  • 10NASA Langley Research Center, Hampton, VA, USA
  • 11Argonne National Laboratory, Argonne, IL, USA
  • 12NOAA National Climatic Data Center, Asheville, NC, USA
  • *currently at: Joint Research Center, European Commission, Ispra, Italy

Abstract. Aerosol variations and trends over different land and ocean regions from 1980 to 2009 are analyzed with the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model and observations from multiple satellite sensors and available ground-based networks. Excluding time periods with large volcanic influence, aerosol optical depth (AOD) and surface concentration over polluted land regions generally vary with anthropogenic emissions, but the magnitude of this association can be dampened by the presence of natural aerosols, especially dust. Over the 30-year period in this study, the largest reduction in aerosol levels occurs over Europe, where AOD has decreased by 40–60% on average and surface sulfate concentrations have declined by a factor of up to 3–4. In contrast, East Asia and South Asia show AOD increases, but the relatively high level of dust aerosols in Asia reduces the correlation between AOD and pollutant emission trends. Over major dust source regions, model analysis indicates that the change of dust emissions over the Sahara and Sahel has been predominantly driven by the change of near-surface wind speed, but over Central Asia it has been largely influenced by the change of the surface wetness. The decreasing dust trend in the North African dust outflow region of the tropical North Atlantic and the receptor sites of Barbados and Miami is closely associated with an increase of the sea surface temperature in the North Atlantic. This temperature increase may drive the decrease of the wind velocity over North Africa, which reduces the dust emission, and the increase of precipitation over the tropical North Atlantic, which enhances dust removal during transport. Despite significant trends over some major continental source regions, the model-calculated global annual average AOD shows little change over land and ocean in the past three decades, because opposite trends in different land regions cancel each other out in the global average, and changes over large open oceans are negligible. This highlights the necessity for regional-scale assessment of aerosols and their climate impacts, as global-scale average values can obscure important regional changes.

Final-revised paper