D. Salcedo

Universidad Nacional Autónoma de México

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J. L. Jiménez

Cooperative Institute for Research in Environmental Sciences

L. T. Molina

Molina Center for Energy and the Environment

K. Džepina

Paul Scherrer Institute

T. Castro

Universidad Nacional Autónoma de México

T. B. Onasch

Aerodyne Research

Mario J. Molina

Universidad Católica Silva Henríquez

Manjula R. Canagaratna

Aerodyne Research

Douglas R. Worsnop

Aerodyne Research

D. R. Worsnop

Aerodyne Research

HÁ

Harry Álvarez‐Ospina

Universidad Nacional Autónoma de México

Cooperative Institutions

Universidad Nacional Autónoma de México

University of Colorado Boulder

Cooperative Institute for Research in Environmental Sciences

Aerodyne Research

Massachusetts Institute of Technology

NSF National Center for Atmospheric Research

National Oceanic and Atmospheric Administration

University of California, Berkeley

NOAA Earth System Research Laboratory

California Institute of Technology

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Nucleation rates of nitric acid dihydrate in 1∶2 HNO₃/H₂O solutions at stratospheric temperatures

Geophysical Research Letters (2000)

D. Salcedo L. T. Molina Mario J. Molina

Nucleation rates of nitric acid dihydrate (NAD) in 1∶2 HNO 3 /H 2 O solutions between 194 and 183 K were measured by observing the freezing behavior of liquid drops with 7 – 33 µm diameter and with concentration of 64 weight percent HNO 3 using an optical microscopy technique. The nucleation rate increases from 3.1×10 5 cm −3 s −1 at 194 K to 1.3x10 9 cm −3 s −1 at 183 K. These results suggest that NAD might not nucleate homogeneously in binary or quasi‐binary nitric acid stratospheric aerosols in relevant time scales.

Nitric acid

10.1029/1999gl010991

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Citations (22)

Equilibrium phase diagrams and water absorption properties of aqueous mixtures of malonic acid and inorganic salts.

AGUFM (2006)

D. Salcedo G. Salgado-Olea

Malonic acid

Aqueous two-phase system

Source

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Citations (0)

Optical properties of atmospheric particles over an urban site in Mexico City and a peri-urban site in Queretaro

Journal of Atmospheric Chemistry (2019)

Rafael N. Liñán-Abanto Oscar Peralta D. Salcedo L. G. Ruíz-Suárez P. Arnott

Dry season

Wet season

Single-scattering albedo

Albedo (alchemy)

10.1007/s10874-019-09394-1

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Citations (10)

Determination of particulate lead using aerosol mass spectrometry: MILAGRO/MCMA-2006 observations

Atmospheric chemistry and physics (2010)

D. Salcedo T. B. Onasch A. C. Aiken Leah R. Williams B. de Foy

Abstract. We report the first measurements of particulate lead (Pb) from Aerodyne Aerosol Mass Spectrometers, which were deployed in and around Mexico City during the Megacity Initiative: Local and Global Research Observations (MILAGRO)/Mexico City Metropolitan Area 2006 (MCMA-2006) field campaigns. The high resolution mass spectrometer of one of the AMS instruments (HR-AMS) and the measured isotopic ratios unequivocally prove the detection of Pb in ambient particles. A substantial fraction of the lead evaporated slowly from the vaporizer of the instruments, which is indicative of species with low volatility at 600 °C. A model was developed in order to estimate the ambient particulate Pb entering the AMS from the signals in the "open" and the "closed" (or "background") mass spectrum modes of the AMS. The model suggests the presence of at least two lead fractions with ~25% of the Pb signal exhibiting rapid evaporation (1/e decay constant, τ<0.1 s) and ~75% exhibiting slow evaporation (τ~2.4 min) at the T0 urban supersite and a different fraction (70% prompt and 30% slow evaporation) at a site northwest from the metropolitan area (PEMEX site). From laboratory experiments with pure Pb(NO3)2 particles, we estimated that the Pb ionization efficiency relative to nitrate (RIEPb) is 0.5. Comparison of time series of AMS Pb with other measurements carried out at the T0 supersite during MILAGRO (using Proton Induced X-ray Emission (PIXE), Inductively-Coupled Plasma Mass Spectrometry (ICP-MS) and single-particle counts from an Aerosol Time-of-Fight Mass Spectrometer (ATOFMS)) shows similar levels (for PIXE and ICP-MS) and substantial correlation. During part of the campaign, sampling at T0 was alternated every 10 min with an Aerosol Concentrator, which enabled the detection of signals for PbCl+ and PbS+ ions. PbS+ displays the signature of a slowly evaporating species, while PbCl+ appears to arise only from fast evaporation, which is likely due to the higher vapor pressure of the compounds generating PbCl+. This is consistent with the evaporation model results. Levels of particulate Pb measured at T0 were similar to previous studies in Mexico City. Pb shows a diurnal cycle with a maximum in the early morning, which is typical of primary urban pollutants. Pb shows correlation with Zn, consistent with previous studies, while the sources of Pb appear to be at least partially disjoint from those of particulate chloride. Back trajectory analysis of the T0 Pb data suggests the presence of sources inside the urban area SSW and N of T0, with different chemical forms of Pb being associated with different source locations. High signals due to particulate lead were also detected in the PEMEX site; again, no correlation between Pb and chloride plumes was observed, suggesting mostly different sources for both species.

10.5194/acp-10-5371-2010

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Citations (56)

Comparative Analysis of Urban Atmospheric Aerosol by Particle-Induced X-ray Emission (PIXE), Proton Elastic Scattering Analysis (PESA), and Aerosol Mass Spectrometry (AMS)

Environmental Science & Technology (2008)

K. S. Johnson Alexander Laskin J. L. Jiménez V. Shutthanandan L. T. Molina

A multifaceted approach to atmospheric aerosol analysis is often desirable in field studies where an understanding of technical comparability among different measurement techniques is essential. Herein, we report quantitative intercomparisons of particle-induced X-ray emission (PIXE) and proton elastic scattering analysis (PESA), performed offline under a vacuum, with analysis by aerosol mass spectrometry (AMS) carried out in real-time during the MCMA-2003 Field Campaign in the Mexico City Metropolitan Area. Good agreement was observed for mass concentrations of PIXE-measured sulfur (assuming it was dominated by SO42−) and AMS-measured sulfate during most of the campaign. PESA-measured hydrogen mass was separated into sulfate H and organic H mass fractions, assuming the only major contributions were (NH4)2SO4 and organic compounds. Comparison of the organic H mass with AMS organic aerosol measurements indicates that about 75% of the mass of these species evaporated under a vacuum. However ∼25% of the organics does remain under a vacuum, which is only possible with low-vapor-pressure compounds, and which supports the presence of high-molecular-weight or highly oxidized organics consistent with atmospheric aging. Approximately 10% of the chloride detected by AMS was measured by PIXE, possibly in the form of metal−chloride complexes, while the majority of Cl was likely present as more volatile species including NH4Cl. This is the first comparison of PIXE/PESA and AMS and, to our knowledge, also the first report of PESA hydrogen measurements for urban organic aerosols.

Mass concentration (chemistry)

Particle (ecology)

10.1021/es800393e

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Citations (44)

Self-association of 1,2-diols Apparent heat capacities of 1,2-diols in n-heptaneand carbon tetrachloride

Journal of the Chemical Society Faraday Transactions (1997)

D. Salcedo Miguel Costas

Apparent molar heat capacities at constant pressure, Cmapp, have been measured for several 1,2-diols in dilute n-heptane and carbon tetrachloride solutions at 25 °C. The systems were: hexane-1,2-diol, octane-1,2-diol and decane-1,2-diol in n-heptane and butane-1,2-diol, pentane-1,2-diol, hexane-1,2-diol, octane-1,2-diol, decane-1,2-diol and dodecane-1,2-diol in carbon tetrachloride; in addition, values of Cmapp for hexan-1-ol and decan-1-ol in carbon tetrachloride were determined. The experimental values of Cmapp show a maximum against diol concentration which is larger and shifted to smaller concentrations than that for the equal carbon number 1-alcohol, indicating that the self-association capability of the 1,2-diols is greater than that of the monoalcohols. The contribution to Cmapp arising from intramolecular H-bonding is small compared to that arising from the intermolecular H-bonds. Diol and monoalcohol self-association is reduced in going from the inert n-heptane to CCl4, which acts as a weak proton acceptor. The data for 1,2-diols when plotted against ψ1, the concentration of hydroxy groups in the mixture, follow a single, corresponding states curve for each of the solvents. To interpret these heat capacity data, an extension of the Treszczanowicz–Kehiaian (TK) model for associated liquids has been undertaken. This extension takes into account the formation of intramolecular H-bonds. The parameters of the model, i.e. equilibrium constants and enthalpies of association, have been fitted to the data. It is concluded that at the dilute 1,2-diol concentrations used here, the heat capacity data can be well explained considering that there is only one predominant species in the solution, viz. pentamers or hexamers.

Heptane

Decane

Pentane

10.1039/a703578k

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Citations (14)

Source Apportionment of Aerosol Mass Spectrometer Data in Pittsburgh, Mexico City, and Houston by Positive Matrix Factorization

AGU Fall Meeting Abstracts (2006)

I. M. Ulbrich Q. Zhang D. Salcedo K. Džepina Manjula R. Canagaratna

Apportionment

Matrix (chemical analysis)

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Citations (1)

Mediciones continuas de carbono negro, monóxido de carbono y dióxido de carbono, durante la temporada seca caliente 2016, en un sitio periurbano de Querétaro, México

CIENCIA & DESARROLLO (2020)

Rafael N. Liñán-Abanto D. Salcedo T. Castro Giovanni Carabeli Oscar Peralta

En Juriquilla-Querétaro, se midió la concentración en masa de carbono negro (BC), la relación de mezcla de monóxido de carbono (CO) y el dióxido de carbono (CO2). Las mediciones se realizaron del 01 de marzo al 30 de abril de 2016. En abril, los valores medios del BC (1.23 µg/m3) y CO (0.30 ppm) fueron mayores a sus correspondientes del mes de marzo (1.08 µg/m3 y 0.26 ppm, respetivamente). El CO2 no sufrió variación en estos meses y mantuvo un valor casi constante de alrededor de 406 ppm. Las tendencias diarias del BC, CO y CO2 fueron similares, con un máximo pronunciado por la mañana y un mínimo por la tarde. Estos contaminantes alcanzaron su valor máximo alrededor de las 08:00-09:00 Hora Local (HL). Se presentó una buena correlación en el ajuste lineal de BC-CO, BC-CO2 y CO-CO2, lo que sugiere que estos contaminantes provendrían de las mismas fuentes. Se observó un efecto fin de semana (valores más bajos del BC, CO y CO2 el fin de semana en comparación con los de días laborables), principalmente en las horas de máximo tráfico.Al no existir estudios de mediciones continuas de BC, CO y CO2; desarrollamos esta investigación para determinar las tendencias diarias de estos contaminantes y sus correlaciones mutuas en una zona periurbana, en Querétaro.

10.33326/26176033.2020.26.934

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Citations (2)

Feasibility of the Detection of Trace Elements in Particulate Matter Using Online High-Resolution Aerosol Mass Spectrometry

Aerosol Science and Technology (2012)

D. Salcedo Alexander Laskin V. Shutthanandan J. L. Jiménez

The feasibility of using an online thermal-desorption electron-ionization high-resolution aerosol mass spectrometer (HR-AMS) for the detection of particulate trace elements was investigated by analyzing data from Mexico City obtained during the MILAGRO 2006 field campaign. This potential application is of interest due to the real-time data provided by the AMS, its high sensitivity and time resolution, and the widespread availability and use of this instrument. High-resolution mass spectral analysis, isotopic ratios, and ratios of different ions containing the same elements are used to constrain the chemical identity of the measured ions. The detection of Cu, Zn, As, Se, Sn, and Sb is reported. There was no convincing evidence for the detection of other trace elements commonly reported in ambient particulate matter (PM). The elements detected tend to be those with lower melting and boiling points, as expected given the use of a vaporizer at 600°C in this instrument. The detection limit (DL) is estimated at approximately 0.3 ng m−3 for 5 min of data averaging. Concentration time series obtained from the AMS data were compared to concentration records determined from offline analysis of particle samples from the same times and locations by inductively coupled plasma based techniques (ICP; PM2.5) and proton-induced X-ray emission (PIXE; PM1.1 and PM0.3). The degree of correlation and agreement between the three instruments (AMS, ICP, and PIXE) varied depending on the element. The AMS shows promise for real-time detection of some trace elements, although additional work including laboratory calibrations with different chemical forms of these elements is needed to further develop this technique and to understand the differences with the ambient data from the other techniques. The trace elements peaked in the morning as expected for primary sources, and the many detected plumes suggest the presence of multiple point sources, probably industrial, in Mexico City, which are variable in time and space, in agreement with previous studies. Copyright 2012 American Association for Aerosol Research

Thermal desorption

Trace element

10.1080/02786826.2012.701354

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Citations (29)

Characterization of ambient aerosols in Mexico City during the MCMA-2003 campaign with Aerosol Mass Spectrometry ? Part II: overview of the results at the CENICA supersite and comparison to previous studies

HAL (Le Centre pour la Communication Scientifique Directe) (2005)

D. Salcedo K. Džepina T. B. Onasch Manjula R. Canagaratna J. T. Jayne

Characterization

Source

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Citations (4)