Aerosol Light Scattering and Absorption at 532 nm at IMP in Mexico City, March 2006

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Aerosol Light Scattering and Absorption at 532 nm
at IMP in Mexico City, March 2006
By Guadalupe Paredes-Miranda and W. Patrick
Arnott Department of Physics and Atmospheric
Sciences University of Nevada Reno Reno Nevada USA

• Photoacoustic measurements of aerosol light
  absorption, and scattering measurements within
  the same instrument using the reciprocal
  nephelometer method.
• Strong variation of aerosol single scattering
  albedo, from primary source driven before
  sunrise, to secondary aerosol driven by mid day.
• Up to 60 of the light scattering is due to
  photochemically generated secondary aerosol at
  mid day.
• Fine particle mass correlates very well with
  aerosol light scattering, likely due to the
  internally mixed character of the aerosol.

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Comparison of Aerosol Light Absorption in 2 Major
Cities
Vegas Jan thru Feb Mexico City March
10-30 Sunrise 645 am Sunset 645 pm
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Average Single Scattering Albedo
Scattering/Extinction
Secondary Aerosol formation (UVVOCs)
Morning rush hour. Large amounts of black carbon
aerosol.
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Average Single Scattering Albedo
Scattering/Extinction
Morning rush hour. Large amounts of black carbon
aerosol.
Regional Mixing Increases
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Aerosol Chemistry and Aerosol Light Scattering in
Mexico City
Aerosol Mass Spec. Chemistry from Jose Jimenez
and Allison Aiken, CU Boulder.
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Chemistry and Optics Primary and Secondary
Aerosol Contributions
Example Fraction of light scattering in Mexico
City due to photochemical production of aerosol.
(from Arnott and Paredes, with AMS supporting
chemistry from Jimenez and Aiken).
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Conclusion

• The key finding is that secondary aerosol has a
  huge impact on Mexico City optics and chemistry.
  
• Secondary aerosol is poorly understood, and
  complicates the role of finding out who is
  responsible for the air pollution so that it can
  be legislated and mitigated.
• It demands clever thought.
• Source profiling and the use of linear models
  for vectoring between primary sources and
  resulting air pollution are suspect.