Atmospheric Environment 39 (2005) 7433–7446 Measurements of CO 2 fluxes from the Mexico City urban landscape Erik Velasco, Shelley Pressley, Eugene Allwine, Hal Westberg, Brian Lamb à Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman, WA 99164-2910, USA Received 28 February 2005; received in revised form 25 August 2005; accepted 25 August 2005 Abstract In a densely populated section of Mexico City, an eddy covariance (EC) flux system was deployed on a tall urban tower to obtain direct measurements of CO 2 emissions from an urban neighborhood located in a subtropical megacity. The measured fluxes and boundary layer conditions satisfy EC assumptions of stationarity, and cospectral analyses of the turbulence measurements exhibit the required boundary layer patterns for acceptable flux measurements. Results from a field experiment conducted during April 2003 show that the urban surface is a net source of CO 2 . The CO 2 flux measurements showed a clear diurnal pattern, with the highest emissions during the morning (up to 1.60mg m 2 s 1 ), and the lowest emissions during nighttime. The measured fluxes were closely correlated to traffic patterns in the area. The mean daily flux was 0.41mgm 2 s 1 , which is similar to that observed in European and US cities. r 2005 Elsevier Ltd. All rights reserved. Keywords: Carbon dioxide fluxes; Eddy covariance; Mexico; Megacity 1. Introduction Urban landscapes are suspected to be major sources of anthropogenic CO 2 ; however, there are few direct measurements of CO 2 emissions in urban areas. Micrometeorological techniques have only recently been applied to urban landscapes, while they have been widely used to measure fluxes of CO 2 , water vapor, volatile organic compounds (VOCs) and other trace gases above vegetation (Baldocchi et al., 2001; Schmid et al., 2000; Westberg et al., 2001). Recent urban studies have focused on cities from developed countries in mid- latitudes, such as Edinburgh (Nemitz et al., 2002), Chicago (Grimmond et al., 2002), Copenhagen (Soegaard and Møller-Jensen, 2003), Basel (Vogt et al., 2003), Tokyo (Moriwaki and Kanda, 2004), Vancouver (Walsh et al., 2004), and Marseille (Grimmond et al., 2004). Despite the fact that three-quarters of the world’s 3 billion urban residents live in developing countries, there have been few, if any, flux measurements in urban areas in developing countries. Mexico City is a good example of an urban area in a less developed country. It is the second largest city in the world, and it is characterized by rapid population growth with a wide range of both direct and indirect CO 2 sources, such as mobile emissions and land use changes due to urbanization. ARTICLE IN PRESS www.elsevier.com/locate/atmosenv 1352-2310/$-see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2005.08.038 à Corresponding author. Tel.: +15093355702; fax: +15093357632. E-mail address: blamb@wsu.edu (B. Lamb).