-
Raul Quintana,
Jesús Serrano,
Virginia Gómez,
Benjamin de Foy,
Javier Miranda,
Claudia Garcia-Cuellar,
Elizabeth Vega,
Inés Vázquez-López, Luisa T Molina,
Natalia Manzano-León,
Irma Rosas,
Alvaro R Osornio-Vargas
[show abstract]
[hide abstract]
ABSTRACT: As part of a field campaign that studied the impact of Mexico City pollution plume at the local, sub-regional and regional levels, we studied transport-related changes in PM(10) composition, oxidative potential and in vitro toxicological patterns (hemolysis, DNA degradation). We collected PM(10) in Mexico City (T(0)) and at a suburban-receptor site (T(1)), pooled according to two observed ventilation patterns (T(0) → T(1) influence and non-influence). T(0) samples contained more Cu, Zn, and carbon whereas; T(1) samples contained more of Al, Si, P, S, and K (p < 0.05). Only SO(4)(-2) increased in T(1) during the influence periods. Oxidative potential correlated with Cu/Zn content (r = 0.74; p < 0.05) but not with biological effects. T(1) PM(10) induced greater hemolysis and T(0) PM(10) induced greater DNA degradation. Influence/non-influence did not affect oxidative potential nor biological effects. Results indicate that ventilation patterns had little effect on intrinsic PM(10) composition and toxicological potential, which suggests a significant involvement of local sources.
Environmental pollution (Barking, Essex: 1987) 09/2011; 159(12):3446-54. · 3.43 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The MILAGRO campaign was a large international field experiments
conduced in Mexico City and Central Mexico during March 2006. We present
an overview of the main findings related to particulate matter and
aerosol radiative properties. PM levels inside Mexico City were similar
or higher than those in the most polluted North American cities, but ~5
times lower than levels in the most polluted Asian megacities During the
study, PM10 and PM2.5 concentrations in the urban area of were about
double the concentrations in the rural areas surrounding Mexico City.
PM2.5 made up about half of the PM10 concentrations, with small amounts
of mass in the PM2.5-PM1.0 range. Mineral matter made up approximately
25% of the PM10 and on average 15% and 28% of the PM2.5 in the urban and
rural areas, respectively. Approximately 25% of the PM2.5 was secondary
inorganic ions with the remaining PM2.5 mass being comprised of largely
carbonaceous aerosol. Except for surface measurements at the central
sampling sites in Mexico city, the elemental carbon mass absorption
efficiency was relatively constant for aircraft and surface measurements
throughout the study, contrary to expectations. Although different
organic aerosol (OA) source apportionment methods had some differences,
there was agreement that the dominant sources of carbonaceous aerosol
were secondary OA (SOA), biomass burning, and mobile sources. The impact
of biomass burning to the aerosol outflow from the region was much
larger than to the surface concentrations inside the city. SOA formation
from primary semivolatile and intermediate volatility precursors has the
potential to close the gap in predicted vs. measured SOA, while
formation from glyoxal also makes an important contribution, especially
to organic oxygen. Biogenic SOA advected from the coastal mountain
ranges contributes about 1 μg m-3 to concentrations in the MCMA.
Primary OA from anthropogenic and biomass burning sources was found to
be semivolatile, while secondary OA was less volatile than POA and aged
SOA was essentially non-volatile, in contradiction with current models.
Growth rates of new particle formation in Mexico City was very large and
found to be impacted by nitrogen containing organic compounds, organic
acids, and hydroxyl organic acids, with only a smaller fraction of
sulfate aerosol. Some open research questions include the following:
additional work is needed to fully quantify the sources of substantial
(30-45%) modern carbon in organic aerosols during low biomass burning
periods. Discrepancies between the two modern carbon datasets deserve
further study. The impact of regional dust vs. road resuspension, as
well as heterogeneous reactions of HNO3 with dust need to be quantified.
The impact of some POA sources such as food cooking, biofuel use, and
open trash burning may be important, but remains poorly characterized.
Some differences in the apportionment of biomass burning PM between
different approaches were observed and need further research, as these
techniques together represent the state of the art for source
apportionment. Anthropogenic SOA predictions are improving in terms of
magnitude but are poorly constrained by the data. More specific
precursor, intermediate, and tracer measurements are needed in future
campaigns. SOA from biomass burning sources, although not dominant in
the city, remains poorly characterized and appears to be underpredicted
by traditional models.
04/2010; 12:2466.
-
[show abstract]
[hide abstract]
ABSTRACT: The molecular processes leading to formation of nanoparticles of blue haze over forested areas are highly complex and not fully understood. We show that the interaction between biogenic organic acids and sulfuric acid enhances nucleation and initial growth of those nanoparticles. With one cis-pinonic acid and three to five sulfuric acid molecules in the critical nucleus, the hydrophobic organic acid part enhances the stability and growth on the hydrophilic sulfuric acid counterpart. Dimers or heterodimers of biogenic organic acids alone are unfavorable for new particle formation and growth because of their hydrophobicity. Condensation of low-volatility organic acids is hindered on nano-sized particles, whereas ammonia contributes negligibly to particle growth in the size range of 3-30 nm. The results suggest that initial growth from the critical nucleus to the detectable size of 2-3 nm most likely occurs by condensation of sulfuric acid and water, implying that anthropogenic sulfur emissions (mainly from power plants) strongly influence formation of terrestrial biogenic particles and exert larger direct and indirect climate forcing than previously recognized.
Proceedings of the National Academy of Sciences 10/2009; 106(42):17650-4. · 9.68 Impact Factor
-
Ryan C Moffet,
Yury Desyaterik,
Rebecca J Hopkins,
Alexei V Tivanski,
Mary K Gilles,
Y Wang,
V Shutthanandan, Luisa T Molina,
Rodrigo Gonzalez Abraham,
Kirsten S Johnson,
Violeta Mugica,
Mario J Molina,
Alexander Laskin,
Kimberly A Prather
[show abstract]
[hide abstract]
ABSTRACT: Recent ice core measurements show lead concentrations increasing since 1970, suggesting new nonautomobile-related sources of Pb are becoming important worldwide (1). Developing a full understanding of the major sources of Pb and other metals is critical to controlling these emissions. During the March, 2006 MILAGRO campaign, single particle measurements in Mexico City revealed the frequent appearance of particles internally mixed with Zn, Pb, Cl, and P. Pb concentrations were as high as 1.14 microg/m3 in PM10 and 0.76 microg/m3 in PM2.5. Real time measurements were used to select time periods of interest to perform offline analysis to obtain detailed aerosol speciation. Many Zn-rich particles had needle-like structures and were found to be composed of ZnO and/or Zn(NO3)2 x 6H2O. The internally mixed Pb-Zn-Cl particles represented as much as 73% of the fine mode particles (by number) in the morning hours between 2-5 am. The Pb-Zn-Cl particles were primarily in the submicrometer size range and typically mixed with elemental carbon suggesting a combustion source. The unique single particle chemical associations measured in this study closely match signatures indicative of waste incineration. Our findings also show these industrial emissions play an important role in heterogeneous processing of NO(y) species. Primary emissions of metal and sodium chloride particles emitted by the same source underwent heterogeneous transformations into nitrate particles as soon as photochemical production of nitric acid began each day at approximately 7 am.
Environmental Science and Technology 11/2008; 42(19):7091-7. · 5.23 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A large study has been undertaken to assess the exposure to diesel exhaust within diesel trucking terminals. A critical component of this assessment is an analysis of the variation in carbonaceous particulate matter (PM) across trucking terminal locations; consistency in the primary sources can be effectively tracked by analyzing trends in elemental carbon (EC) and organic molecular marker concentrations. Ambient samples were collected at yard, dock and repair shop work stations in 7 terminals in the USA and 1 in Mexico. Concentrations of EC ranged from 0.2 to 12 microg m(-3) among the terminals, which corresponds to the range seen in the concentration of summed hopanes (0.5 to 20.5 ng m(-3)). However, when chemical mass balance (CMB) source apportionment results were presented as percent contribution to organic carbon (OC) concentrations, the contribution of mobile sources to OC are similar among the terminals in different cities. The average mobile source percent contribution to OC was 75.3 +/- 17.1% for truck repair shops, 65.4 +/- 20.4% for the docks and 38.4 +/- 9.5% for the terminal yard samples. A relatively consistent mobile source impact was present at all the terminals only when considering percentage of total OC concentrations, not in terms of absolute concentrations.
Journal of Environmental Monitoring 04/2008; 10(3):305-14. · 1.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Characterization of the interaction of hydrogen chloride (HCl) with polar stratospheric cloud (PSC) ice particles is essential to understanding the processes responsible for ozone depletion. The interaction of HCl with ice was studied using a coated-wall flow tube with chemical ionization mass spectrometry (CIMS) between 5x10(-8) and 10(-4) Torr HCl and between 186 and 223 K, including conditions recently shown to induce quasi-liquid layer (QLL) formation on single crystalline ice samples. Measurements were performed on smooth and rough (vapor-deposited) polycrystalline ice films. A numerical model of the coated-wall flow reactor was used to interpret these results and results of studies on zone-refined ice cylinders with grain sizes on the order of several millimeters (reported elsewhere). We found that HCl adsorption on polycrystalline ice films typically used in laboratory studies under conditions not known to induce surface disordering consists of two modes: one relatively strong mode leading to irreversible adsorption, and one relatively weak binding mode leading to reversible adsorption. We have indirect experimental evidence that these two modes of adsorption correspond to adsorption to sites at crystal faces and those at grain boundaries, but there is not enough information to enable us to conclusively assign each adsorption mode to a type of site. Unlike what was observed in the zone-refined ice study, there was no strong qualitative contrast found between the HCl uptake curves under QLL versus non-QLL conditions for adsorption on smooth and vapor-deposited ices. We also found indirect evidence that HCl hexahydrate formation on ice between 3x10(-7) and 2x10(-6) Torr HCl and between 186 and 190 K is a process involving hydrate nucleation and propagation on the crystal surface, rather than one originating in grain boundaries, as has been suggested for ice formed at lower temperatures. These results underscore the dependence of the HCl-ice interaction on the characteristics of the ice substrate.
The Journal of Physical Chemistry A 08/2007; 111(28):6274-84. · 2.95 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Automobile exhaust catalysts using platinum group elements (PGE) have been mandatory on new cars in the Mexico City Metropolitan Area (MCMA) since 1991. Platinum, Pd, Rh, Ir, and Os concentrations and the isotopic composition of Os were determined in PM10 samples from the MCMA. Samples were prepared by isotope dilution NiS fire assay, and analysis was performed by magnetic sector ICP-MS using a single collector instrument for Pt, Pd, Rh, and Ir analysis and a multicollector instrument for Os analysis. Pt, Pd, and Rh concentrations at a downtown location (Merced) increased from < or =1.7 pg of Pt m(-3), 2.7 (4.0) pg of Pd m(-3), and 1.2+/-0.9 pg of Rh m(-3) in 1991 to 9.6 +/- 1.8 pg of Pt m(-3), 10.2+/-1.8 pg of Pd m(-3), and 2.8 +/-0.6 pg of Rh m(-3) in 2003. Concentrations at five sites in MCMA in 2003 averaged 9.3+/-1.9 pg of Pt m(-3), 11+/-4 pg of Pd m(-3), and 3.2+/- 1.0 pg of Rh m(-3). In contrast, Ir and Os concentrations and Os isotopic composition remained relatively constant and were 0.08+/-0.04 pg of Ir m(-3), 0.030 +/-0.007 pg of Os m(-3), and 0.60+/-0.04, respectively, in the MCMA in 2003. Elevated Pt, Pd, and Rh concentrations in the MCMA are attributed to automobile catalysts. A Pt-Pd-Rh concentration peak in 1993 suggests that early catalysts emitted a larger amount of PGE, possibly due to factors inherent in the technology or the use of inappropriate gasoline. Therefore, this study suggests that the current introduction of automobile catalysts in developing countries may result in elevated PGE concentrations if it is not accompanied by infrastructures and policy measures supporting their efficient use.
Environmental Science and Technology 01/2007; 40(24):7554-60. · 5.23 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 1] We present a theoretical estimate of the reaction probability g for the chlorine nitrate (ClONO 2) hydrolysis on type II (water-ice) polar stratospheric cloud material. This estimate is based on high-level ab initio calculations in a supermolecule containing four molecules of water and one molecule of chlorine nitrate. To the best of our knowledge, this is the first estimate of g that makes no a priori use of experimental data at all. Instead, the rate constants for association, surface reaction, and surface desorption as calculated by variational transition state theory enter the model. At 180 K we estimate g % 0.10 À0.06 +0.20 , which is within the error bars of the agreeing recommendations of Jet Propulsion Laboratory and International Union of Pure and Applied Chemistry of 0.3 À0.1 +0.7 . The temperature dependence between 75 and 150 K agrees with results obtained from laser-induced thermal desorption. In particular, the temperature of 105 K above which g becomes less than unity is reproduced well. A negative temperature dependence between 180 and 210 K is found, which has not yet been confirmed in the laboratory for ClONO 2 hydrolysis but only for BrONO 2 on ice. This qualitative agreement of a gas-phase cluster calculation with experiments on hexagonal ice surfaces implies that a highly mobile and oxygen disordered ice surface rather than an ordered, immobile crystalline ice surface is experienced by chlorine nitrate molecules under polar stratospheric conditions.
J. Geophys. Res. 01/2006; 111.
-
[show abstract]
[hide abstract]
ABSTRACT: Based on data from the 1997 Investigación sobre Materia Particulada y Deterioro Atmosférico-Aerosol and Visibility Evaluation Research (IMADA-EVER) campaign and the inorganic aerosol model ISORROPIA, the response of inorganic aerosols to changes in precursor concentrations was calculated. The aerosol behavior is dominated by the abundance of ammonia and thus, changes in ammonia concentration are expected to have a small effect on particle concentrations. Changes in sulfate and nitrate are expected to lead to proportional reductions in inorganic fine particulate matter (PM2.5). Comparing the predictions of ISORROPIA with the observations, the lowest bias and error are achieved when the aerosols are assumed to be in the efflorescence branch. Including crustal species reduces the bias and error for nitrate but does not improve overall model performance. The estimated response of inorganic PM2.5 to changes in precursor concentrations is affected by the inclusion of crustal species in some cases, although average responses are comparable with and without crustal species. Observed concentrations of particle chloride suggest that gas phase concentrations of hydrogen chloride may not be negligible, and future measurement campaigns should include observations to test this hypothesis. Our ability to model aerosol behavior in Mexico City and, thus, design control strategies, is constrained primarily by a lack of observations of gas phase precursors. Future campaigns should focus in particular on better understanding the temporal and spatial distribution of ammonia concentrations. In addition, gas phase observations of nitric acid are needed, and a measure of particle water content will allow stable versus metastable aerosol behavior to be distinguished.
Journal of the Air & Waste Management Association (1995) 07/2005; 55(6):803-15. · 1.52 Impact Factor
-
Journal of the Air & Waste Management Association 10/2004; 54(10):1226-35. · 1.67 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Atmospheric aerosols often contain a substantial fraction of organic matter, but the role of organic compounds in new nanometer-sized particle formation is highly uncertain. Laboratory experiments show that nucleation of sulfuric acid is considerably enhanced in the presence of aromatic acids. Theoretical calculations identify the formation of an unusually stable aromatic acid-sulfuric acid complex, which likely leads to a reduced nucleation barrier. The results imply that the interaction between organic and sulfuric acids promotes efficient formation of organic and sulfate aerosols in the polluted atmosphere because of emissions from burning of fossil fuels, which strongly affect human health and global climate.
Science 07/2004; 304(5676):1487-90. · 31.20 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: About half of the world's population now lives in urban areas because of the opportunity for a better quality of life. Many of these urban centers are expanding rapidly, leading to the growth of megacities, which are defined as metropolitan areas with populations exceeding 10 million inhabitants. These concentrations of people and activity are exerting increasing stress on the natural environment, with impacts at urban, regional and global levels. In recent decades, air pollution has become one of the most important problems of megacities. Initially, the main air pollutants of concern were sulfur compounds, which were generated mostly by burning coal. Today, photochemical smog--induced primarily from traffic, but also from industrial activities, power generation, and solvents--has become the main source of concern for air quality, while sulfur is still a major problem in many cities of the developing world. Air pollution has serious impacts on public health, causes urban and regional haze, and has the potential to contribute significantly to climate change. Yet, with appropriate planning, megacities can efficiently address their air quality problems through measures such as application of new emission control technologies and development of mass transit systems. This review is focused on nine urban centers, chosen as case studies to assess air quality from distinct perspectives: from cities in the industrialized nations to cities in the developing world. While each city--its problems, resources, and outlook--is unique, the need for a holistic approach to the complex environmental problems is the same. There is no single strategy in reducing air pollution in megacities; a mix of policy measures will be needed to improve air quality. Experience shows that strong political will coupled with public dialog is essential to effectively implement the regulations required to address air quality problems.
Journal of the Air & Waste Management Association (1995) 07/2004; 54(6):644-80. · 1.52 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The development and effective implementation of solutions to the air pollution problems in the Mexico City Metropolitan Area is essential to guarantee the health and welfare of its inhabitants. To achieve this, it is essential to have the active and informed participation of the civil society, the academic community, the private sector, and the government, because dealing with pollution requires the use of different strategies in multiple fields of action. The Mexico City case study brings together health, transportation, administration, and many other interdisciplinary approaches to understanding and defeating air pollution. Although focused on the Mexico City area, the work conducted under this case study has significance for developing nations generally. Although policies to reduce air pollution should be based on the best available scientific knowledge, political will and capacity must transform this knowledge into action. This case study has developed a series of recommendations emphasizing the interaction between different disciplines that have provided the foundation for the 10-year air quality management program prepared by the Mexican Metropolitan Environmental Commission.
Annals of the New York Academy of Sciences 07/2004; 1023:142-58. · 3.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Surface properties of aerosols in the Mexico City metropolitan area have been measured in a variety of exposure scenarios related to vehicle emissions in 2002, using continuous, real-time instruments. The objective of these experiments is to describe ambient and occupational particulate polycyclic aromatic hydrocarbon (PAH) concentrations associated with vehicular traffic and facilities using diesel vehicles. Median total particulate PAH concentrations along Mexico City's roadways range from 60 to 910 ng m(-3), averaged over a minimum of 1 h. These levels are approximately 5 times higher than concentrations measured in the United States and among the highest measured ambient values reported in the literature. The ratio of particulate PAH concentration to aerosol active surface area is much higher along roadways and in other areas of fresh vehicle emissions, compared to ratios measured at sites influenced more by aged emissions or noncombustion sources. For particles freshly emitted by vehicles, PAH and elemental carbon (EC) concentrations are correlated because they both originate during the combustion process. Comparison of PAH versus EC and active surface area concentrations at different locations suggests that surface PAH concentrations may diminish with particle aging. These results indicate that exposure to vehicle-related PAH emissions on Mexico City's roadways may present an important public health risk.
Environmental Science and Technology 06/2004; 38(9):2584-92. · 5.23 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Theoretical calculations have been performed to investigate mechanistic features of OH-initiated oxidation reactions of toluene. Aromatic peroxy radicals arising from initial OH and subsequent O(2) additions to the toluene ring are shown to cyclize to form bicyclic radicals rather than undergoing reaction with NO under atmospheric conditions. Isomerization of bicyclic radicals to more stable epoxide radicals possesses significantly higher barriers and, hence, has slower rates than O(2) addition to form bicyclic peroxy radicals. At each OH attachment site, only one isomeric pathway via the bicyclic peroxy radical is accessible to lead to ring cleavage. The study provides thermochemical and kinetic data for quantitative assessment of the photochemical production potential of ozone and formation of toxic products and secondary organic aerosol from toluene oxidation.
Journal of the American Chemical Society 11/2003; 125(41):12655-65. · 9.91 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Using density-functional-plane-wave-based and localized-orbital computational methods, we systematically examine the binding of molecular HCl at a variety of surface sites on crystalline nitric acid trihydrate (NAT), a step preceding the chlorine activation reactions that contribute to the depletion of stratospheric ozone at high latitudes. We pay particular attention to the role played by surface dangling (non-hydrogen-bonding) OH groups. After optimizing six low index faces, we find that NAT(001) and (001̄) faces are thermodynamically the most stable. Only one surface site on the (001) face, with one nearby dangling OH group, exhibits a high affinity for HCl. At this binding site, adsorbed HCl forms a strong H···O hydrogen bond with an NO3- ion and a weaker Cl···H hydrogen bond with a nearby H2O molecule. The interaction energy and enthalpy at 190 K corrected for zero-point energies are 23 and 25 kJ/mol, respectively. The presence of one strong binding site per simulation cell, versus at least three previously reported on the (0001) face of ice Ih (Mantz, Y. A.; Geiger, F. M.; Molina, L. T.; Molina, M. J.; Trout, B. L. J. Phys. Chem. A 2000, 105, 7037), leads to a prediction of a lower HCl surface coverage on NAT than on ice, qualitatively consistent with experiments conducted on these surfaces. Additionally, we present kinetic and thermodynamic evidence that molecular HCl, adsorbed near one or two dangling OH groups, does not dissociate on NAT. By contrast, molecularly adsorbed HCl likely dissociates when interacting strongly with two dangling OH group on the ice Ih (0001) face as reported in previously published theoretical studies (Svanberg, M.; Pettersson, J. B. C.; Bolton, K. J. Phys. Chem. A 2000, 104, 5787; Mantz, Y. A.; Geiger, F. M.; Molina, L. T.; Molina, M. J.; Trout, B. L. Chem. Phys. Lett. 2001, 348, 285).
07/2002;
-
[show abstract]
[hide abstract]
ABSTRACT: DFT and ab initio molecular orbital calculations have been performed to investigate the structures and energetics of the Cl−O2−isoprene peroxy radicals arising from the Cl-initiated oxidation of isoprene. Geometry optimizations of the chloroalkenylperoxy radicals were performed using density function theory (B3LYP), and the energies were computed with the single-point calculation using different levels of theory for electron correlation and basis set effects. At the CCSD(T)/6-31G(d) level of theory corrected with zero-point energy (ZPE), the chloroalkenylperoxy radicals are about 39 to 43 kcal mol-1 more stable than the separated reactants (i.e., O2 + Cl + isoprene). We find no evidence for an energetic barrier to O2 addition and have calculated rate constants for the O2 addition step using canonical variational transition state theory (CVTST) based on Morse potentials to describe the reaction coordinate. The results provide the isomeric branching between the six Cl−O2−isoprene peroxy radicals, indicating that the two β-chloroalkenylperoxy radicals with initial Cl addition at C1 and C4 positions and subsequent O2 addition at C2 and C3 positions,respectively, play an important role in determining the reaction pathways and final product distributions of the Cl−isoprene reaction system.
06/2002;
-
04/2002;
-
04/2002;
-
04/2002;
