1Instituto de Ciencias de la Tierra "Jaume Almera", CSIC. C/ Lluís Solé i Sabarís s/n, 08028 Barcelona, Spain
2Centro Nacional de Investigación y Capacitación Ambiental, CENICA. Periférico 5000, Col. Insurgentes Cuicuilco, C.P. 04530, Delegación Coyoacán, México D.F., Mexico
3Instituto Mexicano del Petróleo, Eje Central Lázaro Cárdenas 152, Col. San Bartolo Atepehuacan. Delegación Gustavo A. Madero. 07730, México, D.F, Mexico
4CIEMAT, Avda. Complutense 22, 28040 Madrid, Spain
Abstract. Levels of PM10, PM2.5 and PM1 and chemical speciation of PM10 and PM2.5 were measured during the MILAGRO campaign (1 to 31 March 2006, but extended in some cases until 6 April) at four urban, one suburban, two rural, two rural background sites with different degree of industrial influence in the Mexico City Metropolitan Area (MCMA) and adjacent regions. PM10 and PM2.5 daily levels varied between 50–56 μg/m³ and 24–46 μg/m³ at the urban sites, 22–35 μg/m³ and 13–25 μg/m³ at the rural sites, and 75 μg/m³ and 31 $\mu $g/m³ at the industrial hotspot, respectively; lower than those recorded at some Asian mega-cities and similar to those recorded at other South American cities. At the urban sites, hourly PM2.5 and PM1 concentrations showed a marked impact of road traffic emissions (at rush hours), with levels of coarse PM remaining elevated during daytime. At the suburban and rural sites, different PM daily patterns were registered according to the influence of the pollution plume from MCMA and also on local soil resuspension.
The speciation studies showed that mineral matter accounted for 25–27% of bulk PM10 at the urban sites and a higher proportion (up to 43%) at the suburban and rural sites. This pattern is repeated in PM2.5, with 15% at urban and 28% at suburban and rural sites. Carbonaceous compounds accounted for a similar proportion at the urban sites (24–32% in PM10, and up to 37% in PM2.5), markedly reduced at the suburban and rural sites (17% in PM10, and 23–38% in PM2.5). The secondary inorganic aerosols accounted for 10–20% of bulk PM10 at urban, suburban, rural and industrial sites, with a higher proportion (40%) at the industrial background site. A relatively high proportion of nitrate in rural sites was present in the coarse fraction.
Typically anthropogenic elements (As, Cr, Zn, Cu, Pb, Sn, Sb, Ba, among others) showed considerably high levels at the urban sites; however levels of particulate Hg and crustal trace elements (Rb, Ti, La, Sc, Ga) were generally higher at the suburban site.
Principal component analysis identified three common factors: crustal, regional background and road traffic. Moreover, some specific factors were obtained for each site.