Aerosol composition and hydrocarbon measurements from the DOE G-1 aircraft during the Megacity Aerosol Experiment in Mexico City (Max-Mex)(Alexander's ASP, PNNL Scope #47789)
EMSL Project ID
15893
Abstract
Atmospheric aerosols are now recognized to give rise to a substantial radiative forcing of climate by scattering and absorbing radiation (direct effects) and by modifying the microphysical, optical, and radiative properties of clouds, affecting their reflectivity and persistence (indirect effects). However the magnitudes of these forcings are quite uncertain. In recognition of this the Department of Energy Atmospheric Science Program (ASP) is focusing on developing enhanced understanding and model-based representation of the processes governing aerosol radiative forcing of climate.Megacities are significant sources of aerosols impacting regional and global scales. The Mexico City Metropolitan Area (MCMA), with 18 million people, is the second largest megacity after Tokyo. In addition to being of intrinsic interest as an example of a megacity that exports aerosols to the global environment, the area provides an opportunity to study aspects of aerosol life cycles in a unique environment characterized by very high concentrations of soot, and secondary aerosols and precursors that can be transported from the megacity into the surrounding region, thereby affecting regional radiative balance.
The DOE Atmospheric Science Program will conduct a 4 week field campaign during February or March 2006, using the DOE G-1 aircraft and two instrumented surface sites. The measurement strategies would be designed to examine the life cycles of aerosols over time scales of approximately 1 to 12 hours. It is hypothesized that over this time scale there will be a substantial shift from primary, emitted aerosols to an internal mixture, resulting in a significant modifications to the optical and CCN properties of aerosols as they age and are advected downwind from the urban source. Secondary aerosol formation is also expected to be observed, with rates and yields that may differ from those observed in U.S. cities because of the higher loadings of reactive gases affecting both concentrations of aerosol precursors and rates of secondary photochemical processes.
This proposal is for the use of the EMSL Time of Flight Aerodyne Mass Spectrometer (AMS-TOF) and the EMSL Proton Transfer Reaction ? Mass Spectrometer (PTR-MS) on the DOE G-1 aircraft. These instruments will be used over the course of a 4 week field campaign encompassing approximately 75 flight hours. The AMS-TOF will be used to characterize aerosol chemical composition as a function of location, atmospheric residence time, and chemical conditions. The AMS, and in particular the TOF version, provides a unique capability to measure size-resolved aerosol chemical composition with a response time commensurate with the rapidly changing conditions experienced by an aircraft flying through an inhomogeneous air mass. The PTR-MS will be used to quantify concentrations of reactive hydrocarbons that are responsible for producing secondary organic aerosol. The PTR-MS allows for continuous measurements, in contrast to other techniques that are based on collecting discrete samples. Both the AMS and PTR-MS have been successfully deployed on the DOE G-1 aircraft in previous field campaigns.
The Max-Mex aircraft flights will be conducted in collaboration with researchers from PNNL, including Michael Alexander, Chris Doran, Rahul Zaveri, and Carl Berkowitz. The timing of the DOE campaign would allow close collaboration with a planned international experiment that will include the NSF Megacity Impact on Regional and Global Environments (MIRAGE) program's Mexico City field study as well as NASA, MIT, and Mexican led components.
Project Details
Project type
Exploratory Research
Start Date
2006-02-01
End Date
2007-03-22
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members