Autores:

Fernando Millán-Vázquez, Rodolfo Sosa-Echevería*, Ana Luisa Alarcón-Jiménez*,
José de Jesús Figueroa-Lara, Miguel Torres-Rodríguez, Brenda Liz Valle-Hernández
y Violeta Mugica-Álvarez

* Ciencias Ambientales | Contaminación Ambiental

Abstract

his study presents the characterization and source apportionment of water-soluble inor-
ganic ions (WSII), contained in particulate matter with an aerodynamic diameter equal to or less than
2.5 µm (PM2.5 ), performed using the positive matrix factorization model (PMF). PM2.5 were collected
in Mexico City from two sites: at Merced (MER), which is a residential location with commercial activ-
ities, and at Metropolitan Autonomous University (UAM), which is located in an industrial area. The
monitoring campaign was carried out across three seasons named Hot Dry (HD) (March–June), Rain
(RA) (July–October), and Cold Dry (CD) (November-February). PM2.5 concentration behavior in both
sites was similar, following the order: CD > HD > RA. The UAM site exhibited higher concentrations
of PM2.5 , of the five cations (Na+ , Mg2+ , Ca2+ , K+ and NH4 + ), and of the four anions (Cl− , SO4 2− ,
NO3 − and PO4 3− ) than MER, since the UAM site is surrounded by several industrial zones. PM2.5
average concentrations for UAM and MER were 28.4 ± 11.2 and 20.7 ± 8.4 µg m−3 , respectively.
The ratio of cation equivalent to anion equivalent (CE/AC) showed that aerosol pH is acidic, which
was confirmed by direct pH measurements. The sulfur oxidation rate (SOR) was 20 times larger
than the nitrogen oxidation rate (NOR). Additionally, SO4 2− was the most abundant ion during the
whole year, especially during the CD season with 5.13 ± 2.5 µg m−3 and 4.9 ± 3.6 µg m−3 for UAM
and MER, respectively, when solar radiation displayed a high intensity. On the opposite side, the
conversion of NO2 to NO3 − , respectively, was low. The air mass backward trajectories were modeled
using the National Oceanic and Atmospheric Administration (NOAA-HYSPLIT), which allowed us
to know that differences in the mass trajectories during the days with higher concentrations were due
to an effect of air recirculation, which favored PM2.5 accumulation and resuspension. On the other
hand, on the days with less PM2.5 , good air dispersion was observed. The main sources identified
with the PMF model were secondary aerosol, vehicular, industrial crustal, and biomass burning for
UAM, while for MER they were vehicular, secondary aerosol, and crustal.

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