The IMADA-AVER Boundary Layer Experiment in the Mexico City Area

Abstract

A boundary layer field experiment in the Mexico City basin during the period 24 February-22 March 1997 is described. A total of six sites were instrumented. At four of the sites, 915-MHz radar wind profilers were deployed and radiosondes were released five times per day. Two of these sites also had sodars collocated with the profilers. Radiosondes were released twice per day at a fifth site to the south of the basin, and rawinsondes were flown from another location to the northeast of the city three times per day. Mixed layers grew to depths of 2500-3500 m, with a rapid period of growth beginning shortly before noon and lasting for several hours. Significant differences between the mixedlayer temperatures in the basin and outside the basin were observed. Three thermally and topographically driven flow patterns were observed that are consistent with previously hypothesized topographical and thermal forcing mechanisms. Despite these features, the circulation patterns in the basin important for the transport and diffusion of air pollutants show less day-today regularity than had been anticipated on the basis of Mexico City's tropical location, high altitude and strong insolation, and topographical setting.

Megacities and Atmospheric Pollution

“…170 The relationship between meteorology and O 3 differs for different episodes. [171][172][173] Air quality measurements for criteria pollutants are reported as IMECA units (Indice Metropolitano de Calidad del Aire, or Metropolitan Index of Air Quality), which are the ratio of a measured concentration to the air quality standard for each pollutant. A contingency program is triggered when the IMECA value exceeds a certain threshold, currently 240 IMECA, or ϳ280 ppb of O 3 .…”

Spatial Differences in Outdoor PM10 Mass and Aerosol Composition in Mexico City

“…5 The climate is generally dry and temperate in this elevated Spatial Differences in Outdoor PM 10 Mass and Aerosol Composition in Mexico City air basin, with frequent and intense thunderstorms from June through October. Detailed meteorological characteristics during the study period are reported by Doran et al 3 Ten long-term PM 10 monitoring sites are operated by the Red Automática de Monitoreo Atmosférico (RAMA) to represent population exposure. As shown in Figure 1, six of these RAMA core sites were supplemented with 21 satellite sites and four urban/regional-scale boundary sites to better understand how well the core sites represent the outdoor exposure of their surrounding population.…”

“…The front Teflon-membrane filter was used to measure mass by gravimetry, light absorption (b abs ) by densitometry, and 40 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Br, Rb, Sr, Y, Zr, Mo, Pd, Ag, Cd, In, Sn, Sb, Ba, La, Au, Hg, Tl, Pb, and U) by X-ray fluorescence (XRF), 9 and the backup citric acid-impregnated cellulose-fiber filter was used to measure gaseous NH 3 by automated colorimetry. On a parallel unit, the front quartz-fiber filter was used to measure water-soluble ions (Na + and K + by atomic absorption spectrometry; 10 Cl -, non-volatilized NO 3 -, and SO 4 2-by ion chromatography 11 ) and carbon [organic carbon (OC) and elemental carbon (EC) by the IMPROVE thermal evolution ], and the backup NaCl-impregnated cellulosefiber filter was used to measure volatilized NO 3 -by ion chromatography. All of the sampling sites used the Teflon/ citric acid filter pack configuration, and about half of the sites used both configurations sampling side by side.…”

“…Si is a good indicator for fugitive dust, b abs is an indicator of vehicle exhaust, and S is an indicator of secondary aerosol. NH 3 (which originates from sewers, animals, and wastewater treatment) reacts with H 2 SO 4 and HNO 3 . Coefficients of >0.8 mean fairly strong correlation, those 0.5-0.8 indicate moderate correlations, and those <0.5 are negligible correlations.…”

“…2 To understand the distribution of PM 10 mass and chemical compositions in the Valle de Mexico, a spatially dense monitoring network was operated from February 23 to March 22, 1997, as part of the Investigación sobre Materia Particulada y Deterioro Atmosférico-Aerosol and Visibility Evaluation Research (IMADA-AVER). 3,4 The objectives of this paper are to (1) examine the nature, causes, and variability of elevated PM 10 concentrations; (2) determine the zones of influence of fugitive dust and other emitters on PM 10 concentrations; and (3) evaluate the zones of representation of fixed site measurements for community exposure to PM 10 .…”