Atmos. Chem. Phys., 7, 2447–2473, 2007 www.atmos-chem-phys.net/7/2447/2007/ Atmospheric © Author(s) 2007. This work is licensed Chemistry under a Creative Commons License. and Physics Air quality in North America’s most populous city – overview of the MCMA-2003 campaign L. T. Molina1,2, C. E. Kolb3, B. de Foy1,2,4, B. K. Lamb5, W. H. Brune6, J. L. Jimenez7,8, R. Ramos-Villegas9, J. Sarmiento9, V. H. Paramo-Figueroa9, B. Cardenas10, V. Gutierrez-Avedoy10, and M. J. Molina1,11 1Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA, USA 2Molina Center for Energy and Environment, La Jolla, CA, USA 3Aerodyne Research, Inc., Billerica, MA, USA 4Saint Louis University, St. Louis, MO, USA 5Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman, WA, USA 6Department of Meteorology, Pennsylvania State University, University Park, PA, USA 7Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO, USA 8Cooperative Institute for Research in the Environmental Sciences (CIRES), Univ. of Colorado at Boulder, Boulder, CO, USA 9Secretary of Environment, Government of the Federal District, Mexico, DF, Mexico 10National Center for Environmental Research and Training, National Institute of Ecology, Mexico, DF, Mexico 11Department of Chemistry and Biochemistry, University of California at San Diego, San Diego, CA, USA Received: 22 February 2007 – Published in Atmos. Chem. Phys. Discuss.: 27 February 2007 Revised: 10 May 2007 – Accepted: 10 May 2007 – Published: 14 May 2007 Abstract. Exploratory field measurements in the Mexico 1 Introduction City Metropolitan Area (MCMA) in February 2002 set the stage for a major air quality field measurement campaign in 1.1 Air pollution in megacities the spring of 2003 (MCMA-2003). Involving over 100 sci- entists from more than 30 institutions in Mexico, the United Degraded air quality in an increasingly urbanized world di- States and Europe, MCMA-2003 revealed important new rectly threatens the health of a large fraction of the world’s insights into the meteorology, primary pollutant emissions, population, impacts the viability of important natural and ambient secondary pollutant precursor concentrations, pho- agricultural ecosystems in regions surrounding highly ur- tochemical oxidant production and secondary aerosol parti- banized areas, and contributes significantly to regional and cle formation in North America’s most populated and pol- global climate change. This challenge is particularly acute in luted megacity. A description of meteorological and atmo- the developing world where the rapid growth of megacities spheric chemistry and aerosol microphysics measurements is producing atmospheric pollution of unprecedented sever- performed during MCMA-2003 is presented. More than 40 ity and extent. There is growing recognition that airborne published or submitted MCMA-2003 research papers are re- emissions from major urban and industrial areas influence viewed and key discoveries pertinent to understanding and both air quality and climate change on scales ranging from improving air quality in Mexico City and similar megacities regional up to continental and global (Decker et al., 2000; in the developing world are summarized. Mayer et al., 2000; Molina and Molina, 2004; Molina et al., 2004). Urban/industrial emissions from the developed world, and increasingly from the megacities (urban centers with popu- lation over 10 millions) of the developing world, change the chemical content of the downwind troposphere in a number Correspondence to: L. T. Molina of fundamental ways (Molina et al., 2004). Emissions of ni- ([email protected]) trogen oxides (NOx), CO and volatile organic compounds Published by Copernicus Publications on behalf of the European Geosciences Union. 2448 L. T. Molina et al.: Overview of the MCMA-2003 campaign ordinated and interdisciplinary manner. The Mexico City Project included active collaboration with Mexican govern- ment officials and decision makers. Although the initial fo- cus of the Integrated Program was on the MCMA, its goal was to develop methods of integrated assessment applicable to other large urban centers throughout the world (Molina and Molina, 2002). 1.2 Air quality in the Mexico City Metropolitan Area Mexico City exhibits the types of environmental problems experienced by megacities around the world and faces the common obstacles to solving them. Air pollution in megaci- ties is strongly influenced by many factors, including topog- Figures Captions raphy, meteorology, industrial growth, transportation needs, and expanding populations. The Mexico City Metropolitan ◦ 0 ◦ 0 Area (19 25 N Latitude and 99 10 W Longitude) lies in an Figures Captions Figures Captions Figure 1. Topographical mapelevated of the basin MCMA at an altitude showing of 2240 the m monitoring above mean seasites level. during MCMA 2 Fig. 1. Topographical map of the MCMA2002/2003 showing campaign: theFigure monitoring 1. Topographical 36 RAMAThe nearlymap stations of the flat MCMA floor (() showing of), theSMA the basin monitoring EHCA covers sites stations about during 5000 MCMA ( km ), CCA-UNAMof Figure 1. TopographicalFigureFigure 1.Figure 1. Topographical Topographicalmap 1. Topographicalof theFigure MCMA map1. map mapTopographical showing ofsitesof of thethe the during MCMAthe monitoringmap MCMA showing of showingshowing the MCMA 2002/2003sites the themonitoring theduring monitoringshowing monitoring campaign:MCMA sites the during monitoringsites sites 36 duringMCMA RAMA during sites MCMA during stations2002/2003MCMA MCMA ( ◦ ),campaign: the 36 Mexican RAMA stations Plateau (() ), andSMA isEHCA confined stations on( ), three CCA-UNAM sides (east, 2002/2003 2002/2003campaign:2002/20032002/2003 36 campaign: RAMAcampaign: campaign: stations2002/2003 36 36 RAMA36 RAMA(() RAMA campaign: ),SMA SMA stationsstations stations EHCAEHCA 36 RAMA(() (()(() stations ), ),SMA), SMA stationsSMA ( (EHCA ),EHCA ), EHCA (() CCA-UNAMCCA-UNAM stations ), SMA stations stations ( networkEHCA ), CCA-UNAM network( ( stations ), CCA-UNAM ), (CCA-UNAM ( (), ), boundary ),boundary CCA-UNAMnetwork sites ( ), boundarysitessouth ( sites ), and (SODAR ), west) SODAR by ( mountain ), ),pilot pilo balloont ridges balloon locations but ( withlocations ), tethered a broad ( open- ), tethered balloon ( ), network (network ), boundarynetworknetwork ( (sites ), ),boundary (boundary( ), ), boundary SODARnetwork sites sites sites( ( ),( ), (boundary pilo ), ), ), SODARSODAR SODARt SODAR balloon sites ( ((locations ( ), ),), pilo), pilot SODAR pilotpilott balloon ( balloon balloonballoon ), (tethered locations ), pilotlocations locations locations balloon balloon( ), tethered ( (( locations ( ), ), tethered ), balloon tethered ( ),( balloontetheredballoon ), ( ( ), ), CENICAing to( the) (Figure north by and M. Zavala.) a narrower gap to the south-southeast. A CENICA ( ) (Figure by M.CENICA Zavala.) ( ) (Fig. by M. Zavala.). CENICA ( ) (Figure by M. Zavala.) CENICA (balloon )balloon (Figure ( (by ), M.), CENICA CENICAZavala.)balloon ( ( ( ) ) ),(Figure(Figure CENICA by ( M.M. ) Zavala.)(FigureZavala.) by M. Zavala.) topographical map of the MCMA is shown in Fig. 1. Figure 2. CirculationFigure Model 2. forCirculation the Mexico Model City for basin the Mexico for O3-S Cityouth, basin O3-North for O3-S outh,and ColdO3-North Surge and Cold Surge During the twentieth century the MCMA experienced episode types. Arrows colored by time of day: early morning (0-5) in blue,Figure morning 2. (6-11) Circulation in Model for the Mexico City basin for O3-South, O3-North and Cold Surge episode types. Arrows colored by time of day: early morning (0-5) in blue, morning (6-11) in huge increases in population and urbanized area as it at- red, afternoon (12-17) in brown(VOCs) and evening drive (18-23) the formationin yellow. Plateau of photochemical winds on O3-South smog days and its red, afternoon (12-17)combine in brown with and vigorous evening mixing (18-23)associated to transport in yellow. the oxidants, Plateauurban plume winds degrading southwards on O3-Southepisode air of the quality days mountains. types. and A low threateningArrows coloredtracted by migrantstime of from day: other early parts morning of the country (0-5) andin blue, industri- morning (6-11) in combine with vigorouslevel mixing jet forms to transportin the Chalco the passageurban plume causing southwards a convergence of the line mountains. in the red,sout hA of afternoonlow the city. Strong (12-17) in brownalization and stimulated evening economic (18-23) growth.in yellow. The populationPlateau winds grew on O3-South days level jet forms in the Chalco passage causing a bothconvergence human line and in the ecosystem south of the health. city. Strong On a larger scale, these westerly flow on O3-North days first enters the basin from the northwest but then comes over the from fewer than 3 million in 1950 to over 18 million in 2000. westerly flow on O3-Northsouth and days west first rims enters of the the basinsame basin during from emissions the the day. northwest The drive combination but the then production with comes combinethe overlow oflevelthe ozone jetwith forms (avigorous a powerful mixing to transport the urban plume southwards of the mountains. A low south and west rims north-southof the basin convergence during the day.zonegreenhouse Theand exhaustcombination of gas) the basinwith in the theto the low free northeast. level troposphere,