An International Megacity Study
U. S. and Mexico plan to study the chemical and physical characteristics of primary and secondary aerosols emitted from Mexico City. Data gathered during the March 2006 Mexico City experiment referred to as the Megacity Initiative: Local And Global Research Observations (MILAGRO) will be used to develop better parameterizations for aerosols in global climate models. Scientists funded by the Office of Sciences Atmospheric Science Program are joining scientists from the National Science Foundation, National Aeronautics and Space Administration, and various Mexican agencies and universities, to study the chemical and physical characteristics of primary and secondary aerosols emitted from Mexico City. Primary aerosols are emitted directly into the atmosphere whereas secondary aerosols are formed in the atmosphere as a result of interactions between numerous gases, such as sulfur dioxide. With a population >10 million, Mexico City is a major source of primary and secondary aerosols that could be affecting weather and climate downwind of the city. Their effect on climate could be to either heat or cool the atmosphere, depending on the magnitude of their direct and indirect effects which have been identified as key uncertainties in climate models. DOE’s Atmospheric Science Program (ASP) [http://www.asp.bnl.gov/MAX-Mex.html] is focused on reducing these uncertainties.