25 results on '"Paredes-Miranda, G."'
Search Results
2. Optical properties of atmospheric particles over an urban site in Mexico City and a peri-urban site in Queretaro
- Author
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Liñán-Abanto, Rafael N., Peralta, O., Salcedo, D., Ruiz-Suárez, L. G., Arnott, P., Paredes-Miranda, G., Alvarez-Ospina, H., and Castro, T.
- Published
- 2019
- Full Text
- View/download PDF
3. BLACK CARBON AEROSOL CONCENTRATION IN FIVE CITIES AND ITS SCALING WITH CITY POPULATION
- Author
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Paredes-Miranda, G., Arnott, W. P., Moosmüller, H., Green, M. C., and Gyawali, M.
- Published
- 2013
4. Mexico City Aerosol Analysis During Milagro Using High Resolution Aerosol Mass Spectrometry at the Urban Supersite (T0) - Part 1: Fine Particle Composition and Organic Source Apportionment
- Author
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Aiken, A. C., Foy, B. de, Wiedinmyer, C., Ulbrich, I. M., Wehrli, M. N., Szidat, S., Prevot, A. S. H., Noda, J., Wacker, L., Volkamer, R., Fortner, E. C., Wang, J., Laskin, A., Shutthanandan, V., Zheng, J., Zhang, R., Paredes-Miranda, G., Arnott, W. P., Molina, Luisa Tan, Sosa, G., Querol, X., Jimenez, J. L., DeCarlo, P. F., Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, and Molina, Luisa Tan
- Abstract
Submicron aerosol was analyzed during the MILAGRO field campaign in March 2006 at the T0 urban supersite in Mexico City with a High-Resolution Aerosol Mass Spectrometer (AMS) and complementary instrumentation. Positive Matrix Factorization (PMF) of high resolution AMS spectra identified a biomass burning organic aerosol (BBOA) component, which includes several large plumes that appear to be from forest fires within the region. Here, we show that the AMS BBOA concentration at T0 correlates with fire counts in the vicinity of Mexico City and that most of the BBOA variability is captured when the FLEXPART model is used for the dispersion of fire emissions as estimated from satellite fire counts. The resulting FLEXPART fire impact factor (FIF) correlates well with the observed BBOA, acetonitrile (CH3CN) [(CH subscript 3 CN)], levoglucosan, and potassium, indicating that wildfires in the region surrounding Mexico City are the dominant source of BBOA at T0 during MILAGRO. The impact of distant BB sources such as the Yucatan is small during this period. All fire tracers are correlated, with BBOA and levoglucosan showing little background, acetonitrile having a well-known tropospheric background of ~100–150 pptv, and PM2.5 [PM subscript 2.5] potassium having a background of ~160 ng m−3 [m superscript -3] (two-thirds of its average concentration), which does not appear to be related to BB sources. We define two high fire periods based on satellite fire counts and FLEXPART-predicted FIFs. We then compare these periods with a low fire period when the impact of regional fires is about a factor of 5 smaller. Fire tracers are very elevated in the high fire periods whereas tracers of urban pollution do not change between these periods. Dust is also elevated during the high BB period but this appears to be coincidental due to the drier conditions and not driven by direct dust emission from the fires. The AMS oxygenated organic aerosol (OA) factor (OOA, mostly secondary OA or SOA) does not show an increase during the fire periods or a correlation with fire counts, FLEXPART-predicted FIFs or fire tracers, indicating that it is dominated by urban and/or regional sources and not by the fires near the MCMA. A new 14C [superscript 14 C] aerosol dataset is presented. Both this new and a previously published dataset of 14C [superscript 14 C] analysis suggest a similar BBOA contribution as the AMS and chemical mass balance (CMB), resulting in 13% higher non-fossil carbon during the high vs. low regional fire periods. The new dataset has ~15% more fossil carbon on average than the previously published one, and possible reasons for this discrepancy are discussed. During the low regional fire period, 38% of organic carbon (OC) and 28% total carbon (TC) are from non-fossil sources, suggesting the importance of urban and regional non-fossil carbon sources other than the fires, such as food cooking and regional biogenic SOA. The ambient BBOA/ΔCH3CN ratio is much higher in the afternoon when the wildfires are most intense than during the rest of the day. Also, there are large differences in the contributions of the different OA components to the surface concentrations vs. the integrated column amounts. Both facts may explain some apparent disagreements between BB impacts estimated from afternoon aircraft flights vs. those from 24-h ground measurements. We show that by properly accounting for the non-BB sources of K, all of the BB PM estimates from MILAGRO can be reconciled. Overall, the fires from the region near the MCMA are estimated to contribute 15–23% of the OA and 7–9% of the fine PM at T0 during MILAGRO, and 2–3% of the fine PM as an annual average. The 2006 MCMA emissions inventory contains a substantially lower impact of the forest fire emissions, although a fraction of these emissions occur just outside of the MCMA inventory are, United States. National Aeronautics and Space Administration (Fellowship NNG04GR06H), United States. National Aeronautics and Space Administration (Fellowship NNG05GQ50H), National Science Foundation (U.S.) (Grant ATM-0528634), National Science Foundation (U.S.) (Grant ATM- 0449815), National Science Foundation (U.S.) (Grant ATM-0810950), National Science Foundation (U.S.) (Grant ATM-0511803), National Science Foundation (U.S.) (Grant ATM-0511769), National Science Foundation (U.S.) (Grant ATM-0528227), United States. Dept. of Energy. Office of Biological and Environmental Research. Atmospheric Science Program (Grant DE-FG02-05ER63981), United States. Dept. of Energy. Office of Biological and Environmental Research. Atmospheric Science Program (Grant DE-FG02-05ER64008), United States. Environmental Protection Agency. (STAR Fellowship RD-83216101-0), Knut and Alice Wallenberg Foundation
- Published
- 2010
5. Mexico City Aerosol Analysis During Milagro Using High Resolution Aerosol Mass Spectrometry at the Urban Supersite (T0) - Part 1: Fine Particle Composition and Organic Source Apportionment.
- Author
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Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Molina, Luisa Tan, Aiken, A. C., Foy, B. de, Wiedinmyer, C., Ulbrich, I. M., Wehrli, M. N., Szidat, S., Prevot, A. S. H., Noda, J., Wacker, L., Volkamer, R., Fortner, E. C., Wang, J., Laskin, A., Shutthanandan, V., Zheng, J., Zhang, R., Paredes-Miranda, G., Arnott, W. P., Sosa, G., Querol, X., Jimenez, J. L., DeCarlo, P. F., Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Molina, Luisa Tan, Aiken, A. C., Foy, B. de, Wiedinmyer, C., Ulbrich, I. M., Wehrli, M. N., Szidat, S., Prevot, A. S. H., Noda, J., Wacker, L., Volkamer, R., Fortner, E. C., Wang, J., Laskin, A., Shutthanandan, V., Zheng, J., Zhang, R., Paredes-Miranda, G., Arnott, W. P., Sosa, G., Querol, X., Jimenez, J. L., and DeCarlo, P. F.
- Abstract
Submicron aerosol was analyzed during the MILAGRO field campaign in March 2006 at the T0 urban supersite in Mexico City with a High-Resolution Aerosol Mass Spectrometer (AMS) and complementary instrumentation. Positive Matrix Factorization (PMF) of high resolution AMS spectra identified a biomass burning organic aerosol (BBOA) component, which includes several large plumes that appear to be from forest fires within the region. Here, we show that the AMS BBOA concentration at T0 correlates with fire counts in the vicinity of Mexico City and that most of the BBOA variability is captured when the FLEXPART model is used for the dispersion of fire emissions as estimated from satellite fire counts. The resulting FLEXPART fire impact factor (FIF) correlates well with the observed BBOA, acetonitrile (CH3CN) [(CH subscript 3 CN)], levoglucosan, and potassium, indicating that wildfires in the region surrounding Mexico City are the dominant source of BBOA at T0 during MILAGRO. The impact of distant BB sources such as the Yucatan is small during this period. All fire tracers are correlated, with BBOA and levoglucosan showing little background, acetonitrile having a well-known tropospheric background of ~100–150 pptv, and PM2.5 [PM subscript 2.5] potassium having a background of ~160 ng m−3 [m superscript -3] (two-thirds of its average concentration), which does not appear to be related to BB sources. We define two high fire periods based on satellite fire counts and FLEXPART-predicted FIFs. We then compare these periods with a low fire period when the impact of regional fires is about a factor of 5 smaller. Fire tracers are very elevated in the high fire periods whereas tracers of urban pollution do not change between these periods. Dust is also elevated during the high BB period but this appears to be coincidental due to the drier conditions and not driven by direct dust emission from the fires. The AMS oxygenated organic aerosol (OA) factor (OOA, mostly secondary OA or SOA) d, United States. National Aeronautics and Space Administration (Fellowship NNG04GR06H), United States. National Aeronautics and Space Administration (Fellowship NNG05GQ50H), National Science Foundation (U.S.) (Grant ATM-0528634), National Science Foundation (U.S.) (Grant ATM- 0449815), National Science Foundation (U.S.) (Grant ATM-0810950), National Science Foundation (U.S.) (Grant ATM-0511803), National Science Foundation (U.S.) (Grant ATM-0511769), National Science Foundation (U.S.) (Grant ATM-0528227), United States. Dept. of Energy. Office of Biological and Environmental Research. Atmospheric Science Program (Grant DE-FG02-05ER63981), United States. Dept. of Energy. Office of Biological and Environmental Research. Atmospheric Science Program (Grant DE-FG02-05ER64008), United States. Environmental Protection Agency. (STAR Fellowship RD-83216101-0), Knut and Alice Wallenberg Foundation
- Published
- 2011
6. Mexico city aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0)-Part 2: Analysis of the biomass burning contribution and the non-fossil carbon fraction
- Author
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National Aeronautics and Space Administration (US), Environmental Protection Agency (US), National Science Foundation (US), Aiken, A.C., De Foy, B., Wiedinmyer, C., Decarlo, P.F., Ulbrich, I.M., Wehrli, M.N., Szidat, S., Prévôt, André S. H., Noda, J., Wacker, L., Volkamer, R., Fortner, E., Wang, J., Laskin, A., Shutthanandan, V., Zheng, J., Zhang, R., Paredes-Miranda, G., Arnott, W.P., Molina, L.T., Sosa, G., Querol, Xavier, Jimenez, J.L., National Aeronautics and Space Administration (US), Environmental Protection Agency (US), National Science Foundation (US), Aiken, A.C., De Foy, B., Wiedinmyer, C., Decarlo, P.F., Ulbrich, I.M., Wehrli, M.N., Szidat, S., Prévôt, André S. H., Noda, J., Wacker, L., Volkamer, R., Fortner, E., Wang, J., Laskin, A., Shutthanandan, V., Zheng, J., Zhang, R., Paredes-Miranda, G., Arnott, W.P., Molina, L.T., Sosa, G., Querol, Xavier, and Jimenez, J.L.
- Abstract
Submicron aerosol was analyzed during the MILAGRO field campaign in March 2006 at the T0 urban supersite in Mexico City with a High-Resolution Aerosol Mass Spectrometer (AMS) and complementary instrumentation. Positive Matrix Factorization (PMF) of high resolution AMS spectra identified a biomass burning organic aerosol (BBOA) component, which includes several large plumes that appear to be from forest fires within the region. Here, we show that the AMS BBOA concentration at T0 correlates with fire counts in the vicinity of Mexico City and that most of the BBOA variability is captured when the FLEXPART model is used for the dispersion of fire emissions as estimated from satellite fire counts. The resulting FLEXPART fire impact factor (FIF) correlates well with the observed BBOA, acetonitrile (CH3CN), levoglucosan, and potassium, indicating that wildfires in the region surrounding Mexico City are the dominant source of BBOA at T0 during MILAGRO. The impact of distant BB sources such as the Yucatan is small during this period. All fire tracers are correlated, with BBOA and levoglucosan showing little background, acetonitrile having a well-known tropospheric background of ∼100-150 pptv, and PM2.5 potassium having a background of ∼160 ng m-3 (two-thirds of its average concentration), which does not appear to be related to BB sources. We define two high fire periods based on satellite fire counts and FLEXPART-predicted FIFs. We then compare these periods with a low fire period when the impact of regional fires is about a factor of 5 smaller. Fire tracers are very elevated in the high fire periods whereas tracers of urban pollution do not change between these periods. Dust is also elevated during the high BB period but this appears to be coincidental due to the drier conditions and not driven by direct dust emission from the fires. The AMS oxygenated organic aerosol (OA) factor (OOA, mostly secondary OA or SOA) does not show an increase during the fire periods or
- Published
- 2010
7. Refining temperature measures in thermal/optical carbon analysis
- Author
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Chow, JC, Watson, JG, Chen, LWA, Paredes-Miranda, G., Chang, MCO, Trimble, D., Fung, KK, Zhang, H., Yu, JZ, Chow, JC, Watson, JG, Chen, LWA, Paredes-Miranda, G., Chang, MCO, Trimble, D., Fung, KK, Zhang, H., and Yu, JZ
- Abstract
Thermal/optical methods have been widely used for quantifying total carbon (TC), organic carbon (OC), and elemental carbon (EC) in ambient and source particulate samples. Thermally defined carbon fractions have been used for source identification. Temperature precision in thermal carbon analysis is critical to the allocation of carbon fractions. The sample temperature is determined by a thermocouple, which is usually located in the oven near the sample. Sample and thermocouple temperature may differ owing to different thermal properties between the sample filter punch and the thermocouple, or inhomogeneities in the heating zone. Quick-drying temperature-indicating liquids (Tempil Inc., South Plainfield, NJ) of different liquefying points are used as temperature calibration standards. These consist of chemicals that change their appearance at specific temperatures and can be optically monitored to determine the sample temperature. Temperature measures were evaluated for three different models of carbon analyzers. Sample temperatures were found to differ from sensor temperatures by 10 to 50 degrees C. Temperature biases of 14 to 22 degrees C during thermal analysis were found to change carbon fraction measurements. The temperature indicators allow calibration curves to be constructed that relate the sample temperature to the temperature measured by a thermocouple.
- Published
- 2005
8. Technical Note: Evaluation of the WRF-Chem "Aerosol Chemical to Aerosol Optical Properties" Module using data from the MILAGRO campaign
- Author
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Barnard, J. C., primary, Fast, J. D., additional, Paredes-Miranda, G., additional, Arnott, W. P., additional, and Laskin, A., additional
- Published
- 2010
- Full Text
- View/download PDF
9. Mexico city aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) – Part 2: Analysis of the biomass burning contribution and the non-fossil carbon fraction
- Author
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Aiken, A. C., primary, de Foy, B., additional, Wiedinmyer, C., additional, DeCarlo, P. F., additional, Ulbrich, I. M., additional, Wehrli, M. N., additional, Szidat, S., additional, Prevot, A. S. H., additional, Noda, J., additional, Wacker, L., additional, Volkamer, R., additional, Fortner, E., additional, Wang, J., additional, Laskin, A., additional, Shutthanandan, V., additional, Zheng, J., additional, Zhang, R., additional, Paredes-Miranda, G., additional, Arnott, W. P., additional, Molina, L. T., additional, Sosa, G., additional, Querol, X., additional, and Jimenez, J. L., additional
- Published
- 2010
- Full Text
- View/download PDF
10. Technical Note: Evaluation of the WRF-Chem "aerosol chemical to aerosol optical properties" module using data from the MILAGRO campaign
- Author
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Barnard, J. C., primary, Fast, J. D., additional, Paredes-Miranda, G., additional, Arnott, W. P., additional, and Laskin, A., additional
- Published
- 2010
- Full Text
- View/download PDF
11. Supplementary material to "Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) – Part 2: Analysis of the biomass burning contribution and the modern carbon fraction"
- Author
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Aiken, A. C., primary, de Foy, B., additional, Wiedinmyer, C., additional, DeCarlo, P. F., additional, Ulbrich, I. M., additional, Wehrli, M. N., additional, Szidat, S., additional, Prevot, A. S. H., additional, Noda, J., additional, Wacker, L., additional, Volkamer, R., additional, Fortner, E., additional, Wang, J., additional, Laskin, A., additional, Shutthanandan, V., additional, Zheng, J., additional, Zhang, R., additional, Paredes-Miranda, G., additional, Arnott, W. P., additional, Molina, L. T., additional, Sosa, G., additional, Querol, X., additional, and Jimenez, J. L., additional
- Published
- 2009
- Full Text
- View/download PDF
12. Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) – Part 2: Analysis of the biomass burning contribution and the modern carbon fraction
- Author
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Aiken, A. C., primary, de Foy, B., additional, Wiedinmyer, C., additional, DeCarlo, P. F., additional, Ulbrich, I. M., additional, Wehrli, M. N., additional, Szidat, S., additional, Prevot, A. S. H., additional, Noda, J., additional, Wacker, L., additional, Volkamer, R., additional, Fortner, E., additional, Wang, J., additional, Laskin, A., additional, Shutthanandan, V., additional, Zheng, J., additional, Zhang, R., additional, Paredes-Miranda, G., additional, Arnott, W. P., additional, Molina, L. T., additional, Sosa, G., additional, Querol, X., additional, and Jimenez, J. L., additional
- Published
- 2009
- Full Text
- View/download PDF
13. Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) – Part 1: Fine particle composition and organic source apportionment
- Author
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Aiken, A. C., primary, Salcedo, D., additional, Cubison, M. J., additional, Huffman, J. A., additional, DeCarlo, P. F., additional, Ulbrich, I. M., additional, Docherty, K. S., additional, Sueper, D., additional, Kimmel, J. R., additional, Worsnop, D. R., additional, Trimborn, A., additional, Northway, M., additional, Stone, E. A., additional, Schauer, J. J., additional, Volkamer, R. M., additional, Fortner, E., additional, de Foy, B., additional, Wang, J., additional, Laskin, A., additional, Shutthanandan, V., additional, Zheng, J., additional, Zhang, R., additional, Gaffney, J., additional, Marley, N. A., additional, Paredes-Miranda, G., additional, Arnott, W. P., additional, Molina, L. T., additional, Sosa, G., additional, and Jimenez, J. L., additional
- Published
- 2009
- Full Text
- View/download PDF
14. Primary and secondary contributions to aerosol light scattering and absorption in Mexico City during the MILAGRO 2006 campaign
- Author
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Paredes-Miranda, G., primary, Arnott, W. P., additional, Jimenez, J. L., additional, Aiken, A. C., additional, Gaffney, J. S., additional, and Marley, N. A., additional
- Published
- 2009
- Full Text
- View/download PDF
15. Supplementary material to "Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) – Part 1: Fine particle composition and organic source apportionment"
- Author
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Aiken, A. C., primary, Salcedo, D., additional, Cubison, M. J., additional, Huffman, J. A., additional, DeCarlo, P. F., additional, Ulbrich, I. M., additional, Docherty, K. S., additional, Sueper, D., additional, Kimmel, J. R., additional, Worsnop, D. R., additional, Trimborn, A., additional, Northway, M., additional, Stone, E. A., additional, Schauer, J. J., additional, Volkamer, R., additional, Fortner, E., additional, de Foy, B., additional, Wang, J., additional, Laskin, A., additional, Shutthanandan, V., additional, Zheng, J., additional, Zhang, R., additional, Gaffney, J., additional, Marley, N. A., additional, Paredes-Miranda, G., additional, Arnott, W. P., additional, Molina, L. T., additional, Sosa, G., additional, and Jimenez, J. L., additional
- Published
- 2009
- Full Text
- View/download PDF
16. Closure on the single scattering albedo in the WRF-Chem framework using data from the MILAGRO campaign
- Author
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Barnard, J. C., primary, Fast, J. D., additional, Paredes-Miranda, G., additional, and Arnott, W. P., additional
- Published
- 2009
- Full Text
- View/download PDF
17. Primary and secondary contributions to aerosol light scattering and absorption in Mexico City during the MILAGRO 2006 campaign
- Author
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Paredes-Miranda, G., primary, Arnott, W. P., additional, Jimenez, J. L., additional, Aiken, A. C., additional, Gaffney, J. S., additional, and Marley, N. A., additional
- Published
- 2008
- Full Text
- View/download PDF
18. The T1-T2 study: evolution of aerosol properties downwind of Mexico City
- Author
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Doran, J. C., primary, Barnard, J. C., additional, Arnott, W. P., additional, Cary, R., additional, Coulter, R., additional, Fast, J. D., additional, Kassianov, E. I., additional, Kleinman, L., additional, Laulainen, N. S., additional, Martin, T., additional, Paredes-Miranda, G., additional, Pekour, M. S., additional, Shaw, W. J., additional, Smith, D. F., additional, Springston, S. R., additional, and Yu, X.-Y., additional
- Published
- 2007
- Full Text
- View/download PDF
19. The T1-T2 study: evolution of aerosol properties downwind of Mexico City
- Author
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Doran, J. C., primary, Arnott, W. P., additional, Barnard, J. C., additional, Cary, R., additional, Coulter, R., additional, Fast, J. D., additional, Kassianov, E. I., additional, Kleinman, L., additional, Laulainen, N. S., additional, Martin, T., additional, Paredes-Miranda, G., additional, Pekour, M. S., additional, Shaw, W. J., additional, Smith, D. F., additional, Springston, S. R., additional, and Yu, X.-Y., additional
- Published
- 2006
- Full Text
- View/download PDF
20. Refining temperature measures in thermal/optical carbon analysis
- Author
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Chow, J. C., primary, Watson, J. G., additional, Chen, L.-W. A., additional, Paredes-Miranda, G., additional, Chang, M.-C. O., additional, Trimble, D., additional, Fung, K. K., additional, Zhang, H., additional, and Zhen Yu, J., additional
- Published
- 2005
- Full Text
- View/download PDF
21. Technical Note: Evaluation of the WRF-Chem "Aerosol Chemical to Aerosol Optical Properties" Module using data from the MILAGRO campaign.
- Author
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Barnard, J. C., Fast, J. D., Paredes-Miranda, G., Arnott, W. P., and Laskin, A.
- Subjects
ATMOSPHERIC chemistry ,PHOTOACOUSTIC spectroscopy ,AEROSOLS ,OPTICAL properties - Abstract
A comparison between observed aerosol optical properties from the MILAGRO field campaign, which took place in the Mexico City Metropolitan Area (MCMA) during March 2006, and values simulated by the Weather Research and Forecasting (WRF-Chem) model, reveals large differences. To help identify the source of the discrepancies, data from the MILAGRO campaign are used to evaluate the "aerosol chemical to aerosol optical properties" module implemented in the full chemistry version of the WRF-Chem model. The evaluation uses measurements of aerosol size distributions and chemical properties obtained at the MILAGRO T1 site. These observations are fed to the module, which makes predictions of various aerosol optical properties, including the scattering coefficient, B
scat ; the absorption coefficient, Babs ; and the single-scattering albedo, ω0 ; all as a function of time. Values simulated by the module are compared with independent measurements obtained from a photoacoustic spectrometer (PAS) at a wavelength of 870 nm. Because of line losses and other factors, only "fine mode" aerosols with aerodynamic diameters less than 2.5 μm are considered here. Over a 10-day period, the simulations of hour-by-hour variations of Bscat are not satisfactory, but simulations of Babs and ω0 are considerably better. When averaged over the 10-day period, the computed and observed optical properties agree within the uncertainty limits of the measurements and simulations. Specifically, the observed and calculated values are, respectively: (1) Bscat , 34.1±5.1Mm-1 versus 30.4±3.4Mm-1 ; (2) Babs , 9.7±1.0Mm-1 versus 11.7±1.2Mm-1 ; and (3) ω0 , 0.78±0.05 and 0.74±0.03. The discrepancies in values of ω0 simulated by the full WRF-Chem model thus cannot be attributed to the "aerosol chemistry to optics" module. The discrepancy is more likely due, in part, to poor characterization of emissions near the T1 site, particularly black carbon emissions. [ABSTRACT FROM AUTHOR]- Published
- 2010
- Full Text
- View/download PDF
22. Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) - Part 2: Analysis of the biomass burning contribution and the modern carbon fraction.
- Author
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Aiken, A. C., de Foy, B., Wiedinmyer, C., DeCarlo, P. F., Ulbrich, I. M., Wehrli, M. N., Szidat, S., Prevot, A. S. H., Noda, J., Wacker, L., Volkamer, R., Fortner, E., Wang, J., Laskin, A., Shutthanandan, V., Zheng, J., Zhang, R., Paredes-Miranda, G., Arnott, W. P., and Molina, L. T.
- Abstract
Submicron aerosol was analyzed during the MILAGRO field campaign in March 2006 at the T0 urban supersite in Mexico City with a High-Resolution Aerosol Mass Spectrometer (AMS) and complementary instrumentation. Positive Matrix Factorization (PMF) of high resolution AMS spectra identified a biomass burning OA (BBOA) component, which includes several large plumes that appear to be from forest fires within the region. Here, we show that the AMS BBOA concentration at T0 correlates with fire counts in the vicinity of Mexico City and that most of the BBOA variability is captured when the FLEXPART model is used for the dispersion of fire emissions as estimated from satellite fire counts. The resulting FLEXPART fire impact index correlates well with the observed BBOA, CH
3 CN, levoglucosan, and potassium, indicating that wildfires in the region surrounding Mexico City are the dominant source of BBOA at T0 during MILAGRO. The impact of distant BB sources such as the Yucatan is small during this period. All fire tracers are correlated, with BBOA and levoglucosan showing little background, acetonitrile having a well-known tropospheric background of ∼100- 150 ppt, and PM2.5 potassium having a background of ∼160 ngm-3 (two-thirds of its average concentration), which does not appear to be related to BB sources. We define two high fire periods based on satellite fire counts and predicted fire impacts. We then compare these periods with a low fire period when the impact of regional fires is about a factor of 5 smaller. Fire tracers are very elevated in the high fire periods whereas tracers of urban pollution do not change between these periods. Dust is also elevated during the high BB period but this appears to be coincidental due to the drier conditions and not driven by direct dust emission from the fires. The AMS oxygenated OA factor (OOA, mostly secondary OA or SOA) does not show an increase during the fire periods or a correlation with fire counts, FLEXPART-predicted fire impacts or fire tracers, indicating that it is dominated by urban and/or regional sources and not by the fires near the MCMA. A new14 C aerosol dataset is presented. Both this new and a previously published dataset of14 C analysis suggest a similar BBOA contribution as the AMS and chemical mass balance (CMB), resulting in 15% higher modern carbon during the high vs. low regional fire periods. The new dataset has ∼15% more fossil carbon on average than the previously published one, and possible reasons for this discrepancy are discussed. During the low regional fire period, 37% of organic carbon (OC) and 30% total carbon (TC) are from modern sources, suggesting the importance of urban and regional modern carbon sources other than the fires, such as food cooking and regional biogenic SOA. Overall, the fires from the region near the MCMA are estimated to contribute 15-23% of the OA and 7-9% of the fine PM at T0 during MILAGRO, and 2-3% of the fine PM as an annual average. The 2006 MCMA emissions inventory contains a substantially lower impact of the forest fire emissions, although a fraction of these emissions occur just outside of the MCMA inventory area. The ambient BBOA/ΔCH3 CN ratio is much higher in the afternoon when the wildfires are most intense than during the rest of the day, which may explain some disagreements between BB impacts from afternoon aircraft flights and those from 24-h ground measurements. Finally, we show that there are large differences in the contributions of the different OA components to the surface concentrations vs. the integrated column amounts. [ABSTRACT FROM AUTHOR]- Published
- 2009
- Full Text
- View/download PDF
23. Closure on the single scattering albedo in the WRF-Chem framework using data from the MILAGRO campaign.
- Author
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Barnard, J. C., Fast, J. D., Paredes-Miranda, G., and Arnott, W. P.
- Abstract
Data from the MILAGRO field campaign, which took place in the Mexico City Metropolitan Area (MCMA) during March 2006, is used to perform a closure experiment between aerosol chemical properties and aerosol optical properties. Measured aerosol chemical properties, obtained from the MILAGRO T1 site, are fed to two different "chemical to optical properties" modules. One module uses a sectional approach and is identical to that used in the WRF-Chem model, while the other is based on a modal approach. This modal code is employed as an independent check on the WRF-Chem module. Both modules compute aerosol optical properties and, in particular, the single-scattering albedo, ω¯
0 , as a function of time. The single-scattering albedos are compared to independent measurements obtained from a photoacoustic spectrometer (PAS). Because chemical measurements of the aerosol coarse mode were not available, and the inlet of the PAS could not ingest aerosols larger than about 2 to 3 μm, we focus here on the fine-mode ω¯0 . At 870 nm, the wavelength of the PAS measurements, the agreement between the computed (modal and WRF-Chem) and observed fine-mode ω¯0 , averaged over the course of the campaign, is reasonably good. The observed ω¯0 value is 0.77, while for both modules, the calculated value was 0.75 resulting in a difference of 0.02 between observations and both computational approaches. This difference is less than the uncertainty of the observed ω¯0 values (6%, or 0.05), and therefore "closure" is achieved, at least for mean values. After adjusting some properties of black carbon absorption and mass concentration within plausible uncertainty limits, the two modules simulate well the diurnal variation of ω¯0 , and the absorption coefficient, Babs , but are less successful in calculating the variation of the scattering coefficient, Bscat . This difficulty is probably caused by the presence of larger particles during the day when windblown dust is ubiquitous; this dust likely increases the proportion of large particles introduced into the PAS. The dust also contributes to a very large aerosol mass loading in the coarse mode, and neglect of the coarse mode may cause significant errors, estimated to be as large as 0.07, in the calculation and measurement of ambient ω¯0 . Finally, the observed ω¯0 is compared to the ω¯0 computed by the full WRF-Chem model, which includes prognostic aerosol chemistry. Unlike the results discussed above, a comparison between observed and simulated ω¯0 values reveals major differences. This large discrepancy is probably due, in part, to poor characterization of emissions near the T1 site, particularly black carbon emissions. [ABSTRACT FROM AUTHOR]- Published
- 2009
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24. Primary and secondary contributions to aerosol light scattering and absorption in Mexico City during the MILAGRO 2006 campaign.
- Author
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Paredes-Miranda, G., Arnott, W. P., Jimenez, J. L., Aiken, A. C., Gaffney, J. S., and Marley, N. A.
- Abstract
A photoacoustic spectrometer, a nephelometer, an aetholemeter, and an aerosol mass spectrometer were used to measure at ground level real-time aerosol light absorption, scattering, and chemistry at an urban site located in north east Mexico City (Instituto Mexicano del Petroleo, Mexican Petroleum Institute, denoted by IMP), as part of the Megacity Impact on Regional and Global Environments field experiment, MILAGRO, in March 2006. Photoacoustic and reciprocal nephelometer measurements at 532nm accomplished with a single instrument compare favorably with conventional measurements made with an aethelometer and a TSI nephelometer. The diurnally averaged single scattering albedo at 532nm was found to vary from 0.60 to 0.85 with the peak value at midday and the minimum value at 7 a.m. local time, indicating that the Mexico City plume is likely to have a net warming effect on local climate. The peak value is associated with strong photochemical generation of secondary aerosol. It is estimated that the same-day photochemical production of secondary aerosol (inorganic and organic) is approximately 40 percent of the aerosol mass concentration and light scattering in association with the peak single scattering albedo. A strong correlation of aerosol scattering at 532nm and total aerosol mass concentration was found, and an average mass scattering efficiency factor of 3.8m
2 /g was determined. Comparisons of photoacoustic and aethalometer light absorption with oxygenated organic aerosol concentration (OOA) indicate a very small systematic bias of the filter based measurement associated with OOA and the peak aerosol single scattering albedo. [ABSTRACT FROM AUTHOR]- Published
- 2008
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25. The T1-T2 study: Evolution of aerosol properties downwind of Mexico City
- Author
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Doran, J. C., Barnard, J. C., Arnott, W. P., Cary, R., Coulter, R., Fast, J. D., Kassianov, E. I., Kleinman, L., Laulainen, N. S., Martin, T., Paredes-Miranda, G., Pekour, M. S., Shaw, W. J., Smith, D. F., Springston, S. R., Xiao-Ying Yu, Pacific Northwest National Laboratory (PNNL), Desert Research Institute, Sunset Laboratory, Inc., Argonne National Laboratory [Lemont] (ANL), Brookhaven National Laboratory [Upton, NY] (BNL), U.S. Department of Energy [Washington] (DOE)-UT-Battelle, LLC-Stony Brook University [SUNY] (SBU), State University of New York (SUNY)-State University of New York (SUNY), and EGU, Publication
- Subjects
lcsh:Chemistry ,[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere ,010504 meteorology & atmospheric sciences ,lcsh:QD1-999 ,13. Climate action ,[SDU.OCEAN] Sciences of the Universe [physics]/Ocean, Atmosphere ,010501 environmental sciences ,01 natural sciences ,lcsh:Physics ,lcsh:QC1-999 ,0105 earth and related environmental sciences - Abstract
International audience; As part of a major atmospheric chemistry and aerosol field program carried out in March of 2006, a study was conducted in the area to the north and northeast of Mexico City to investigate the evolution of aerosols and their associated optical properties in the first few hours after their emission. The focus of the T1-T2 aerosol study was to investigate changes in the specific absorption ?ABS (absorption per unit mass, with unit of m2 g?1) of black carbon as it aged and became coated with compounds such as sulfate and organic carbon, evolving from an external to an internal mixture. Such evolution has been reported in previous studies. The T1 site was located just to the north of the Mexico City metropolitan area; the T2 site was situated approximately 35 km farther to the northeast. Nephelometers, particle soot absorption photometers, photoacoustic absorption photometers, and organic and elemental carbon analyzers were used to measure the optical properties of the aerosols and the carbon concentrations at each of the sites. Radar wind profilers and radiosonde systems helped to characterize the meteorology and to identify periods when transport from Mexico City over T1 and T2 occurred. Organic and elemental carbon concentrations at T1 showed diurnal cycles reflecting the nocturnal and early morning buildup from nearby sources, while concentrations at T2 appeared to be more affected by transport from Mexico City. Specific absorption during transport periods was lower than during other times, consistent with the likelihood of fresher emissions being found when the winds blew from Mexico City over T1 and T2. The specific absorption at T2 was larger than at T1, which is also consistent with the expectation of more aged particles with encapsulated black carbon being found at the more distant location. In situ measurements of single scattering albedo with an aircraft and a ground station showed general agreement with column-averaged values derived from rotating shadowband radiometer data, although some differences were found that may be related to boundary-layer evolution.
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