Aerosol Characterization and Radiative Forcing Assessment Using Satellite Data and Models
M. Chin/L. Remer
October 26, 2012 15:26:07
Description of Problem
Aerosols affect the Earth’s energy budget directly by scattering and absorbing radiation and indirectly by acting as cloud condensation nuclei and, thereby, affecting cloud properties. Aerosols can be transported thousands of miles downwind, thereby having important implications for climate change and air quality on a wide range of scales. Enhanced new satellite passive sensors introduced in the last decade, the emerging measurements of aerosol vertical distributions from space-borne lidars provided the opportunity to attempt measurement-based characterization of aerosol and assessment of aerosol radiative forcing. Such satellite-based methods can play a role in extending temporal and spatial scale of field campaigns and evaluating and constraining model simulations. On the other hand, model simulations and measurements from field campaigns can provide essential parameters that satellites don’t observe. The overall goal of this research is to characterize aerosol distributions and assess the aerosol radiative forcing through an integration of multiple satellite observations and model simulations.
Scientific Objectives and Approach
We address the scientific problems by integrating surface and satellite remote sensing measurements and model simulations. During the past year, we conducted three major tasks: (1) examining daytime variations of aerosols over Americas using AERONET measurements in supporting GEO-CAPE science definition; (2) exploring the estimate of above-cloud aerosol by integrating complementary measurements from multiple A-Train sensors; and (3) assessing climate impacts of anthropogenic aerosol intercontinental transport using source-receptor relationship simulations from multiple chemical transport models.
1. Daytime variations of aerosols in the Americas. We analyze the daytime variation of aerosol with seasonal distinction by using multiyear measurements from 54 of AERONET sites over the Americas. The analysis shows a wide range of daily variability of aerosol optical depth (AOD) and Ångström exponent depending on location and season (Zhang et al., 2012). Possible reasons for daytime variations are given. The largest AOD daytime variation range at 440 nm, up to 75%, occurs in Mexico City, with maximum AOD in the afternoon. Large AOD daily variations are also observed in the polluted mid-Atlantic United States and West Coast with maximum AOD occurring in the afternoon in the mid-Atlantic United States, but in the morning in the West Coast. In South American sites during the biomass burning season, maximum AOD generally occurs in the afternoon. But the daytime variation becomes smaller when sites are influenced more by long-range transported smoke than by local burning. The diverse patterns of aerosol daytime variation suggest that geostationary satellite measurements would be invaluable for characterizing aerosol temporal variations on regional and continental scales. In particular, simultaneous measurements of aerosols and aerosol precursors from a geostationary satellite would greatly aid in understanding the evolution of aerosol as determined by emissions, chemical transformations, and transport processes.
2. Estimate of above-cloud aerosol from an integration of A-Train measurements. We conduct an integrated analysis of aerosols above clouds by using multi-sensor A-Train measurements, including CALIOP, OMI, and MODIS (Yu et al., 2012). The analysis of Saharan dust outflow and Southwest African smoke outflow regions shows that the CALIOP above-cloud AOD correlates positively with OMI aerosol index (AI) (a qualitative measure of aerosol loading) in an approximately linear manner, and that the AOD/AI ratio decreases with increasing cloud optical depth (COD). The COD-dependence of AOD/AI ratio doesn’t depend on aerosol type when potential biases in the CALIOP AOD measurements are empirically accounted for. Our results may suggest the potential of combining OMI AI and MODIS cloud measurements to empirically derive above-cloud AOD with a spatial coverage much more extensive than CALIOP measurements, which needs to be further explored in the future.
3. Climate impacts of anthropogenic aerosol intercontinental transport. We assess changes of AOD and direct radiative forcing (DRF) in response to the reduction of anthropogenic emissions in four major pollution regions in the northern hemisphere by using results from 9 global chemical transport models. The impacts of the regional emission reductions on AOD and DRF are extended well beyond the source regions because of the aerosol intercontinental transport. On annual basis, the relative contribution of aerosol import by intercontinental transport accounts for 10-30% of the overall impacts by both the domestic emissions and intercontinental transport, depending on regions and species. While South Asia is most influenced by import of sulfate aerosol from Europe, North America is most influenced by import of black carbon from East Asia. It is found that the model simulations show large spread, highlighting a need of improving aerosol processes in models and evaluating and constraining models with observations. Some of the analysis has contributed to the HTAP 2010 Assessment report (West et al., 2011) and a more complete analysis will soon be submitted to a scientific journal.
Other achievements include: (a) contributing a set of aerosol direct forcing calculations to the AeroCom experiments; (b) detecting modifications of cloud properties by aerosols from A-Train satellite measurements (Yuan et al., 2011a; Yuan et al., 2011b); and (c) deriving the optical properties for “pure” dust by analyzing long-term AERONET measurements.
Refereed Journal Publications
Kim, D., M. Chin, H. Yu, T. F. Eck, A. Sinyuk, A. Smirnov, and B. N. Holben, 2011: Dust optical properties over North Africa and Arabian Peninsula derived from the AERONET dataset, Atmospheric Chemistry and Physics, 11, 10733-10741, doi:10.5194/acp-11-10733-2011.
Yu, H., Y. Zhang, M. Chin, Z. Liu, A. Omar, L. A. Remer, Y. Yang, T. Yuan, and J. Zhang, 2012: An integrated analysis of aerosol above clouds from A-Train multi-sensor measurements, Remote Sensing of Environment, 46, doi:10.1016/j.rse.2012.01.011. (in press)
Yuan, T., L. A. Remer, and H. Yu, 2011a: Microphysical, macrophysical and radiative signatures of volcanic aerosols in trade wind cumulus observed by the A-Train, Atmospheric Chemistry and Physics, 11, 7119-7132, doi:10.5194/acp-11-7119-2011.
Yuan, T., L. A. Remer, K. E. Pickering, and H. Yu, 2011b: Observational evidence of aerosol enhancement of lightning activity and convective invigoration, Geophysical Research Letters, 38, L04701, doi:10.1029/2010GL046052.
Zhang, Y., H. Yu, T. F. Eck, A. Smirnov, M. Chin, L. A. Remer, H. Bian, Q. Tan, R. Levy, B. N. Holben, and S. Piazzolla, 2012: Aerosol daytime variations over North and South America derived from multiyear AERONET measurements, Journal of Geophysical Research – Atmospheres, 117, doi:10.1029/2011JD017242. (in press)
Other Publications and Conferences
West, J. J., L. Emberson, E. Ainsworth, S. C., Anenberg, S. Arnold, M. Ashmore, R. Atkinson, N. Bellouin, A. Cohen, B. Collins, P. Delmelle, R. Doherty, N. Farah, J. Fuhrer, K. Hicks, T. Holloway, K. Kobayashi, J. Liu, D. Mauzerall, L. Mercado, G. Mills, M. Sanderson, D. Shindell, S. Sitch, D. Stevenson, J. Tuovinen, R. van Dingenen, J. Wang, H. Yu, and C. Zdanowicz, 2011: Impacts on Health, Ecosystems, and Climate, Chapter 5 in Hemispheric Transport of Air Pollution 2010, Part A: Ozone and Particulate Matter, Air Pollution Studies No. 17, Edited by Frank Dentener, Terry Keating, and Hajime Akimoto, Prepared by the Task Force on Hemispheric Transport of Air Pollution acting within the framework of the Convention on Long-range Transboundary Air Pollution, United Nations, New York and Geneva, 2011.
Yu, H., Assessing Impact of Aerosol Intercontinental Transport on Regional Air Quality and Climate: What satellites can help. INVITED, Goldschmidt Conference, Prague, Czech Republic, August 14-19, 2011.
Yu, H., Y. Zhang, M. Chin, Z. Liu, A. Omar, L.A. Remer, Y. Yang, T. Yuan, and J. Zhang, CALIPSO-AURA-AQUA integrated analysis of aerosols-above-clouds, CALIPSO/CloudSat Science Team Meeting, Montreal, Quebec, Canada, June 15-17, 2011.
Yu, H., M. Chin, S. Kondragunta, and C. Xu, Possibilities for detecting cloud-free pixels and retrieving aerosols on hourly basis – An analysis of NOAA GOES-12 Measurements and implications for GEO-CAPE mission, GEO-CAPE Community Workshop, Boulder, Colorado, May 11-13, 2011.
Zhang, Y., H. Yu, A. Smirnov, T.F. Eck, M. Chin, L.A. Remer, Q. Tan, R. Levy, Aerosol Daytime Variations over North and South Americas as Derived from Multiyear AERONET Measurements, GEO-CAPE Community Workshop, Boulder, Colorado, May 11-13, 2011.