Megacities and the effects of urbanization

Whereas in the past, meteorology and climatology were separate fields, be it only because of disparate time (and length scales as well), it appears today that the two fields are strongly coupled, not only as the climate gives the boundaries for investigating the weather, but also because localized events can influence the larger climatological scales. The specific items on which ESSL scientists focused in this year are related to the role of aerosols in climate and weather, to the coupling of eco-systems, biochemistry and climate, to climate change, climate variability and extreme weather such as hurricanes, to interactions of the water cycle with climate and weather, to the impacts of climate and weather on society and ecosystems and finally to megacities and the effects of urbanization; the latter priority is a highlight for NCAR and concerns the international multi-agency field campaign that took place in Mexico city and combined interactive modeling as well. The laboratory highlights are related to the role of aerosols, to the regional carbon cycle, to a numerical simulation of turbulence, to landfall of hurricanes, to the global and regional water cycles and to polar climate.

MIRAGE/MILAGRO [NAR Highlight] - ACD
Texas air quality study - ACD

MIRAGE/MILAGRO

	The NCAR/NSF C-130 aircraft sampling air just east of Mexico City on 19 March 2006. Heavy air pollution is evident below flight altitude. This photograph was taken from the NASA DC-8 aircraft during a wingtip-to-wingtip intercomparison (photo Jim Crawford). High resolution figure

I. Historical background

The export of pollutants from urban to regional and global environments is a major concern because of wide-ranging potential consequences for human health and cultivated and natural ecosystems in terms of visibility degradation, weather modification, changes in radiative forcing, and tropospheric oxidation (self-cleaning) capacity.   Megacities in developing countries are of particular concern because of their rapid growth, limited urban planning, and lags in technological approaches aimed at reducing emissions. ACD scientists have targeted Mexico City for intensive study of pollution export because of its large size, excellent collaborations with local researchers, adequate infrastructure, and the availability of urban air quality monitoring networks and emissions inventories needed to specify the initial state of the exported air.

II. Relationship to NCAR Strategic Plan

The need for a better scientific understanding of the origin and fate of atmospheric contaminants is one of the pillars upon which the 2006 NCAR Strategic Plan is erected ( Strategic Goal #1: Improve understanding of the atmosphere, the Earth system, and the Sun ), and the role of megacities is specifically identified therein ( p. 18 ).

III. Description

MIRAGE-Mex (Megacities Impacts on Regional And Global Environments – Mexico City case study) is a project consisting of an intensive observational period (IOP) of coordinated aircraft and ground-based measurements supported by extensive modeling and satellite observations.   The overall scientific objectives of MIRAGE-Mex are:

- Characterization of the extent, persistence, and potential impacts of the Mexico City plume in the surrounding regions.

- Increased understanding of the evolution of gas-phase reactivity over the urban-to-regional-to-global scale transition.

- Increased understanding of the physical and chemical evolution of aerosols and their radiative properties over the urban-to-regional-to-global transition.

- Increased understanding of the gas-aerosol interactions over the urban-to-regional-to-global transition.

IV. Timeframe

In 2002, the MIRAGE-Mex project was formally started through an open workshop held at NCAR, in which the atmospheric science community worked with ACD scientists to identify the major scientific uncertainties to be addressed in a field campaign. This was followed by intensive coordination and organizational activities to ensure opportunities for full participation by scientists from academia, government agencies, and other institutions.   Partnerships were established between MIRAGE-Mex and projects from other agencies, particularly DOE (MAX-Mex), NASA (INTEX-B), and the Mexican government (MCMA-2006), thus leveraging resources toward comprehensive, simultaneous, coordinated observations spanning urban, regional, and larger scales.   The IOP took place 1-30 March 2006.    Analysis andinterpretation of this unique and rich data set is ongoing and expected to continue over the next several years.  

In the longer time frame, it is prudent to assume that burgeoning urbanization will increasingly contaminate the regional and global atmosphere.   The 2006 MIRAGE-Mex project will provide important scientific knowledge of the transport and transformations of pollutants.   However, additional studies in different seasons (e.g. wet and dry) and different megacities will be required.   Thus, MIRAGE is intended to be a long-term program, in accordance with NCARs commitment to its Strategic Plan.

V. Accomplishments overview from FY 2006

A. Tasks completed.

1.  In October 2005, ACD scientists hosted and led a meeting of the scientists participating in MIRAGE-Mex and the related field campaigns, in which they finalized the coordination of the many observations, modeling and forecasting activities, and logistic support.

2. ACD scientists improved instruments and installed them on the NSF C-130 aircraft, in preparation for the IOP.   This was particularly challenging since the division was relocated only two months before the IOP.   Scientists from ACD, MMM, DOE, NASA, and several universities collaborated on the development of chemistry-transport models for forecasting and flight planning. The NCAR MOZART and NCAR/NOAA WRF-Chem models were used prominently during the IOP.

3. The IOP was carried out successfully during 1-30 March.   Approximately 100 Mexican and 320 non-Mexican scientists participated in the MIRAGE-Mex IOP and coordinated projects.

4. Post-mission data analysis was carried out by individual ACD researchers, and submitted to a central data archive on schedule (1 Sept. 2006).

B. Outputs realized to date

Preliminary observational and model data were submitted to a central data archive, on schedule. The preliminary data are available to all participants.

C. Outcomes realized to date

Not yet available, pending complete analysis of this very large data set.

VI. MIRAGE evaluation measures for coming year(s):

A. Planned Inputs

Analysis of data is ongoing.   Approximately 30 ACD scientists will be involved in the analysis, modeling, and publication of the data.   ACD scientists will host the First Science Meeting in October 2006, in which researchers will present their individual results and begin collaborative analysis of multiple data sets.   The Second Science Meeting will take place in Mexico, tentatively in May 2007.

Numerous resultant publications are anticipated over the next two years, and plans are underway for collecting them as a special issue of a major international scientific journal. Special sessions are being planned for the Fall'07 AGU and other international and national meetings.

B. Milestones

1. Targets and objectives

The primary objective of MIRAGE-Mex is to better understand how urban emissions impact regional and global atmospheric composition.   This increased understanding will be reported in scientific publications over the next several years, and used to evaluate and improve predictive models of the atmosphere.

2. Outputs (deliverables)

- On 1 March 2007, the final MIRAGE data will become available to all participants.  

- On 1 March 2008, the data archive will become publicly available.

- The majority of resultant publications are expected to appear over the 2007-2008 time period, and a few beyond. Many presentations at conferences, including special sessions, are planned over this same time period.

- A formal report to the Mexican government is scheduled for delivery in May 2007.

C. Expected outcome of MIRAGE

The MIRAGE-Mex results will provide the Mexican government with the first-ever assessment of the regional pollution problem surrounding Mexico City, and a better understanding of the relative importance of different sources (e.g. urban vs. biomass burning).   

Scientifically, the results will allow evaluation and improvement of predictive models of atmospheric composition.   Because MIRAGE-Mex focuses on understanding processes (e.g. gas-aerosol-radiation interactions), the knowledge gained from MIRAGE-Mex will be, at least in part, applicable to other megacities for which measurements are sparse or non-existent.

VII. Impact of the MIRAGE

MIRAGE-Mex provides a regional “snapshot” of how the global atmosphere may look in the future. By evaluating and improving numerical models of pollutant transport and transformations, it will increase their credibility in predicting future impacts on the environment and climate, and enable studies of atmospheric composition changes under different scenarios of growth, socio-economic status, and technological improvements. This information is central to the formulation of scientifically sound policy options.

VIII. List of the entities that have sponsored MIRAGE. 

Funded by: NSF, DOE, NASA, NOAA, USFS, and various Mexican agencies.

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Texas air quality study

	Figure 1. The left side of the rack contains the PANs instrument on the NOAA P3 during the TexAQS 2006 campaign. High resolution figure

The Texas Air Quality Study (TEXAQS 2006) was a NOAA led field campaign out of Houston, Texas, that focused on providing a more complete understanding of the sources and processes responsible for photochemical pollution (ozone) and regional haze (aerosols) during the summer in Texas.   Ozone and aerosols both play important roles in air quality and climate change as a result of their chemical and radiative properties.   A significant fraction of ozone in the troposphere is produced photochemically from precursors that have both anthropogenic and natural sources.   Major urban centers are a large source of these precursors, which results in elevated levels of ozone on local and regional scales from production and transport.   These elevated levels can be a human health hazard in urban and surrounding areas and can impact ecosystems in both urban and rural areas.   Enhanced aerosol production in urban areas can also impact human health and ecosystems.   Exposure to high levels of aerosols can lead to respiratory problems for humans and can acidify ecosystems as they are removed by rain.  

The study area was Texas and the northwestern Gulf of Mexico. The field campaign was designed to address the following research areas:

• Emissions verification and assessment - How well do current inventories represent actual emissions for: cities, point sources, ships, and vegetation?
• Transport and mixing – What are the relevant amount of pollution imported to Texas and exported from the continental boundary layer to the marine boundary layer and the free troposphere?
• Chemical transformation – How do gaseous and aerosol emissions evolve chemically and physically as they are transported away from the source regions to the remote atmosphere?
• Aerosol properties and radiative effects – What are the chemical, physical, and optical properties of the aerosol in this region and how do these properties affect regional haze and aerosol direct and indirect forcing of climate?
• Forecast models – What is the current skill of air quality forecast models on local, regional and global scales and what improvements can be made to enhance the accuracy and extend the periods of these forecasts?

On the NOAA P3 aircraft, ACD scientists measured PANs and collected whole air samples for analysis of non-methane hydrocarbons, halocarbons, alkyl nitrates, and oxygenated VOCs. Figure 1 shows the PANs instrument on the P3. The campaign was conducted in September-October, 2006.

Plans for FY 2007 include analysis of mixing ratios and distributions of the various compounds and associated photochemistry in chemical and power plant plumes, the Houston ship channel, greater urban areas, rural areas, and over the northwest Gulf of Mexico. This work was funded by NOAA and NSF/NCAR.

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