A24A-01
Overview of the Megacity Aerosol Experiment: Mexico City (MAX-Mex)
Tropospheric aerosols can play an important role the radiative balance of the globe. This is due to their ability to scatter and absorb solar radiation. The sign of this forcing will depend on their chemical composition and size, their lifetimes, and position in the atmosphere. Major sources of aerosols are now coming from megacities: Cities with more than 10 million population. As part of the MILAGRO campaign, the Megacity Aerosol Experiment: Mexico City was conducted by the Atmospheric Science Program of the Climate Change Research Division of the Department of Energy in collaboration with the scientists supported by NSF, NASA, and Mexican agencies. The preliminary results of the study will be overviewed and highlights of the efforts from both ground based and airborne measurements presented. Data from the study confirm that the megacity plumes are significant sources of both primary and secondary aerosols into the regional scale, and black carbon and secondary aerosols are contributing to single scattering albedos in the Valley of Mexico and downwind that are substantially reduced when compared to other areas (such as the eastern United States). The potential of biomass burning as well as megacity plumes contributing to a decrease in the aerosol single scattering albedos (aerosol direct effects) on regional scales will be discussed. This work was performed as part of the Department of Energy's Megacity Aerosol Experiment - Mexico City under the support of the Atmospheric Science Program. "This researchwas supported by the Office of Science (BER), U. S. Department of Energy, Grant No. DE-FG02-07ER64328.
A24A-02
An overview of J-31 aircraft measurements in the Megacity Initiative Local and Global Research Observations (MILAGRO) experiment
In March 2006 the J-31 flew a suite of instruments to measure solar energy in the atmosphere and how it is affected by aerosols, water vapor, clouds, and Earth surfaces. The goal was to better understand the impacts of these constituents and surfaces on climate and to advance spaceborne and airborne measurement science. The J-31 carried meteorological and navigational instruments, plus four core science instruments: Ames Airborne Tracking Sunphotometer (AATS-14), Solar Spectral Flux Radiometer (SSFR), Research Scanning Polarimeter (RSP), and Cloud Absorption Radiometer (CAR). Specific objectives were to: (1) Characterize aerosols and water vapor flowing from Mexico City and biomass fires toward and over the Gulf of Mexico, (2) Quantify the ability of satellites and airborne lidar to retrieve aerosol, cloud, and water vapor properties, (3) Characterize surface spectral albedo and bidirectional reflectance to help constrain satellite retrievals, (4) Quantify relationships between the above and aerosol amount and type. The J-31 made 13 flights (4 over Mexico City, 9 over the Gulf of Mexico) coordinated with the satellites Aura, Aqua, Terra, and Parasol. Several flights coordinated with the NASA Langley King Air B-200, which carried a High Spectral Resolution Lidar (HSRL) and two passive remote sensors. One flight coordinated with the DC-8 over Mexico City and one with both the C-130 and the B-200 over the Gulf of Mexico. We summarize goals, methods and sample results to provide context for other J-31 presentations at this conference.
A24A-03
Intercontinental Transport of Aerosols: Implication for Regional Air Quality
Aerosol particles, also known as PM2.5 (particle diameter less than 2.5 μm) and PM10 (particle diameter less than 10 μm), is one of the key atmospheric components that determine ambient air quality. Current US air quality standards for PM10 and PM2.5 are 50 μg/m3 and 15 μg/m3, respectively. While local and regional emission sources are the main cause of air pollution problems, aerosols can be transported on a hemispheric or global scale. In this study, we use the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model to quantify contributions of long-range transport vs. local/regional pollution sources and from natural vs. anthropogenic sources to PM concentrations different regions. In particular, we estimate the hemispheric impact of anthropogenic sulfate aerosols and dust from major source areas on other regions in the world. The GOCART model results are compared with satellite remote sensing and ground-based network measurements of aerosol optical depth and concentrations.
A24A-04 INVITED
Regional and Global Perspective of Megacity Air Pollution
Megacities are leading drivers of economic and environmental change. Fueled by high population growth and vibrant economies, energy consumption in megacities are large and growing. In Asia megacities are projected to account for ~40% of their country's GNP (gross national product) by 2030. Because fossil fuels will provide much of this energy, emissions of greenhouse gases and air pollutants such as sulfur and nitrogen oxides and particulates could dramatically increase. Without strong intervention the situation will inevitably worsen. The motorization of urban environments all around the world has produced local smog in hundreds of cities. In aggregate, pollution from megacities and surrounding areas can grow to create regional and global problems. The current interest in transboundary and hemispheric transport of pollutants reflect this. The pressing environmental problems of urban pollution and climate change are closely linked megacity problems sharing common causes and solutions. The fact that air pollution problems and greenhouse gas emissions arise largely from fossil fuel combustion and the important role of aerosols in both air pollution and climate change are illustrative examples. Globally many megacities represent atmospheric brown cloud hotspots; regions with large aerosol radiative forcing of the atmosphere and surface (dimming), with annual mean surface dimming in most tropical mega cities exceeding 20 Wm-2, equivalent to reducing solar irradiance at the top of the atmosphere by more than 10%. The increase in solar energy absorbed by aerosols over the atmosphere of some of these mega cities is comparable to the heat input by energy consumption. Thus in addition to contributing to regional and global climate change, the atmospheric forcing may also contribute to the urban heat island effect. In this paper the impacts of megacities on regional and global pollution are discussed, drawing upon finding from current international activities including MILAGRO, ABC, and GURME.
A24A-05 INVITED
Policy Implications of Air Quality Research and Co-benefit to Climate Change
In recent decades air pollution has become one of the most important problems of megacities and large urban centers. Photochemical smog induced from motorization, industrial activities, power generation, and solvents, has now become the main source of concern for air quality. Air pollution has serious impacts on public health and ecosystems, causes urban and regional haze, and has the potential to contribute significantly to climate change. While an integrated approach is required to address air pollution problems to achieve and sustain improvements, policy strategies must be based on a solid understanding of the pollutant emissions and atmospheric processes that lead to unacceptable levels of air quality. This talk will address the air pollution problems in the Mexico City Metropolitan Area and other large urban centers in Mexico, and the strategies undertaken by the Mexican authorities to improve air quality and reduce greenhouse gas emissions.