메뉴 건너뛰기




Volumn 113, Issue 12, 2008, Pages

Chemically segregated optical and microphysical properties of ambient aerosols measured in a single-particle mass spectrometer

Author keywords

[No Author keywords available]

Indexed keywords

ATMOSPHERIC AEROSOLS; ATMOSPHERIC CHEMISTRY; ATMOSPHERIC DENSITY; ATMOSPHERIC HUMIDITY; ATMOSPHERIC OPTICS; REFRACTIVE INDEX;

EID: 50049116034     PISSN: 01480227     EISSN: None     Source Type: Journal    
DOI: 10.1029/2007JD009393     Document Type: Article
Times cited : (50)

References (44)
  • 1
    • 0034640239 scopus 로고    scopus 로고
    • Reduction of tropical cloudiness by soot
    • doi:10.1126/ science.288.5468.1042
    • Ackerman, A. S., O. B. Toon, D. E. Stevens, A. J. Heymsfield, V. Ramanathan, and E. J. Welton (2000), Reduction of tropical cloudiness by soot, Science, 288(5468), 1042-1047, doi:10.1126/ science.288.5468.1042.
    • (2000) Science , vol.288 , Issue.5468 , pp. 1042-1047
    • Ackerman, A.S.1    Toon, O.B.2    Stevens, D.E.3    Heymsfield, A.J.4    Ramanathan, V.5    Welton, E.J.6
  • 3
    • 33947613050 scopus 로고    scopus 로고
    • Chemical and microphysical characterization of ambient aerosols with the aerodyne aerosol mass spectrometer
    • doi:10.1002/ mas.20115
    • Canagaratna, M. R., et al. (2007), Chemical and microphysical characterization of ambient aerosols with the aerodyne aerosol mass spectrometer, Mass Spectrom. Rev., 26(2), 185-222, doi:10.1002/ mas.20115.
    • (2007) Mass Spectrom. Rev , vol.26 , Issue.2 , pp. 185-222
    • Canagaratna, M.R.1
  • 5
    • 0000039392 scopus 로고    scopus 로고
    • Thermodynamic model of the system H+-NH4+- Na+-SO42-- NO3 --Cl-- H2O at 298.15 K
    • doi:10.1021/jp973043j
    • Clegg, S. L., P. Brimblecombe, and A. S. Wexler (1998), Thermodynamic model of the system H+-NH4+- Na+-SO42-- NO3 --Cl-- H2O at 298.15 K, J. Phys. Chem. A, 102(12), 2155-2171, doi:10.1021/jp973043j.
    • (1998) J. Phys. Chem. A , vol.102 , Issue.12 , pp. 2155-2171
    • Clegg, S.L.1    Brimblecombe, P.2    Wexler, A.S.3
  • 6
    • 33847769006 scopus 로고    scopus 로고
    • Laboratory and ambient particle density determinations using light scattering in conjunction with aerosol mass spectrometry
    • doi:10.1080/02786820701199736
    • Cross, E. S., J. G. Slowik, P. Davidovits, J. D. Allan, D. R. Worsnop, J. T. Jayne, D. K. Lewis, M. Canagaratna, and T. B. Onasch (2007), Laboratory and ambient particle density determinations using light scattering in conjunction with aerosol mass spectrometry, Aerosol Sci. Technol., 41, 343-359, doi:10.1080/02786820701199736.
    • (2007) Aerosol Sci. Technol , vol.41 , pp. 343-359
    • Cross, E.S.1    Slowik, J.G.2    Davidovits, P.3    Allan, J.D.4    Worsnop, D.R.5    Jayne, J.T.6    Lewis, D.K.7    Canagaratna, M.8    Onasch, T.B.9
  • 7
    • 0028406759 scopus 로고
    • Discrete-dipole approximation for scattering calculations
    • Draine, B. T., and P. J. Flatau (1994), Discrete-dipole approximation for scattering calculations, J. Opt. Soc. Am. A, 11(4), 1491-1499.
    • (1994) J. Opt. Soc. Am. A , vol.11 , Issue.4 , pp. 1491-1499
    • Draine, B.T.1    Flatau, P.J.2
  • 9
    • 0031572710 scopus 로고    scopus 로고
    • Real-time analysis of individual atmospheric aerosol particles: Design and performance of a portable ATOFMS
    • doi:10.1021/ac970540n
    • Gard, E., J. E. Mayer, B. D. Morrical, T. Dienes, D. P. Fergenson, and K. A. Prather (1997), Real-time analysis of individual atmospheric aerosol particles: Design and performance of a portable ATOFMS, Anal. Chem., 69(20), 4083-4091, doi:10.1021/ac970540n.
    • (1997) Anal. Chem , vol.69 , Issue.20 , pp. 4083-4091
    • Gard, E.1    Mayer, J.E.2    Morrical, B.D.3    Dienes, T.4    Fergenson, D.P.5    Prather, K.A.6
  • 10
    • 7144235823 scopus 로고    scopus 로고
    • Direct observation of heterogeneous chemistry in the atmosphere
    • doi:10.1126/science.279.5354.1184
    • Gard, E. E., et al. (1998), Direct observation of heterogeneous chemistry in the atmosphere, Science, 279(5354), 1184-1187, doi:10.1126/science.279.5354.1184.
    • (1998) Science , vol.279 , Issue.5354 , pp. 1184-1187
    • Gard, E.E.1
  • 11
    • 85012471588 scopus 로고    scopus 로고
    • Determination of particle effective density in urban environments with a differential mobility analyzer and aerosol particle mass analyzer
    • doi:10.1080/02786820600803925
    • Geller, M., S. Biswas, and C. Sioutas (2006), Determination of particle effective density in urban environments with a differential mobility analyzer and aerosol particle mass analyzer, Aerosol Sci. Technol., 40(9), 709-723, doi:10.1080/02786820600803925.
    • (2006) Aerosol Sci. Technol , vol.40 , Issue.9 , pp. 709-723
    • Geller, M.1    Biswas, S.2    Sioutas, C.3
  • 12
    • 34250706626 scopus 로고    scopus 로고
    • Aerosol properties and processes: A path from field and laboratory measurements to global climate models
    • doi:10.1175/BAMS-88-7-1059
    • Ghan, S. J., and S. E. Schwartz (2007), Aerosol properties and processes: A path from field and laboratory measurements to global climate models, Bull. Am. Meteorol. Soc., 88(7), 1059-1083, doi:10.1175/BAMS-88-7-1059.
    • (2007) Bull. Am. Meteorol. Soc , vol.88 , Issue.7 , pp. 1059-1083
    • Ghan, S.J.1    Schwartz, S.E.2
  • 13
    • 33751220804 scopus 로고    scopus 로고
    • Physicochemical properties of nitrate aerosols: Implications for the atmosphere
    • doi:10.1021/jp063821k
    • Gibson, E. R., P. K. Hudson, and V. H. Grassian (2006), Physicochemical properties of nitrate aerosols: Implications for the atmosphere, J. Phys. Chem. A, 110(42), 11785-11799, doi:10.1021/jp063821k.
    • (2006) J. Phys. Chem. A , vol.110 , Issue.42 , pp. 11785-11799
    • Gibson, E.R.1    Hudson, P.K.2    Grassian, V.H.3
  • 14
    • 25444465861 scopus 로고    scopus 로고
    • Design, modeling, optimization and experimental tests of a particle beam width probe for the Aerodyne aerosol mass spectrometer
    • doi:10.1080/02786820500423782
    • Huffman, J. A., J. T. Jayne, F. Drewnick, A. C. Aiken, T. Onasch, D. R. Worsnop, and J. L. Jimenez (2005), Design, modeling, optimization and experimental tests of a particle beam width probe for the Aerodyne aerosol mass spectrometer, Aerosol Sci. Technol., 39, 1143-1163, doi:10.1080/02786820500423782.
    • (2005) Aerosol Sci. Technol , vol.39 , pp. 1143-1163
    • Huffman, J.A.1    Jayne, J.T.2    Drewnick, F.3    Aiken, A.C.4    Onasch, T.5    Worsnop, D.R.6    Jimenez, J.L.7
  • 16
    • 0037105693 scopus 로고    scopus 로고
    • Evolution of nitrogen species air pollutants along trajectories crossing the Los Angeles area
    • doi:10.1021/es0110630
    • Hughes, L. S., J. O. Allen, L. G. Salmon, P. R. Mayo, R. J. Johnson, and G. R. Cass (2002), Evolution of nitrogen species air pollutants along trajectories crossing the Los Angeles area, Environ. Sci. Technol., 36(18), 3928-3935, doi:10.1021/es0110630.
    • (2002) Environ. Sci. Technol , vol.36 , Issue.18 , pp. 3928-3935
    • Hughes, L.S.1    Allen, J.O.2    Salmon, L.G.3    Mayo, P.R.4    Johnson, R.J.5    Cass, G.R.6
  • 17
    • 34247370602 scopus 로고    scopus 로고
    • Intergovernmental Panel on Climate Change , Cambridge Univ. Press, New York
    • Intergovernmental Panel on Climate Change (2007), Climate Change 2007: The Physical Science Basis, Cambridge Univ. Press, New York.
    • (2007) Climate Change 2007: The Physical Science Basis
  • 18
    • 0035825677 scopus 로고    scopus 로고
    • Strong radiative heating due to the mixing state of black carbon in atmospheric aerosols
    • doi:10.1038/35055518
    • Jacobson, M. Z. (2001), Strong radiative heating due to the mixing state of black carbon in atmospheric aerosols, Nature, 409(6821), 695-697, doi:10.1038/35055518.
    • (2001) Nature , vol.409 , Issue.6821 , pp. 695-697
    • Jacobson, M.Z.1
  • 19
    • 33750025838 scopus 로고    scopus 로고
    • Aerosol composition and source apportionment in the Mexico City Metropolitan Area with PIXE/PESA/ STIM and multivaniate analysis
    • Johnson, K. S., B. de Foy, B. Zuberi, L. T. Molina, M. J. Molina, Y. Xie, A. Laskin, and V. Shutthanandan (2006), Aerosol composition and source apportionment in the Mexico City Metropolitan Area with PIXE/PESA/ STIM and multivaniate analysis, Atmos. Chem. Phys., 6, 4591-4600.
    • (2006) Atmos. Chem. Phys , vol.6 , pp. 4591-4600
    • Johnson, K.S.1    de Foy, B.2    Zuberi, B.3    Molina, L.T.4    Molina, M.J.5    Xie, Y.6    Laskin, A.7    Shutthanandan, V.8
  • 20
    • 0345975881 scopus 로고    scopus 로고
    • Modification of aerosol mass and size distribution due to aqueous-phase SO2 oxidation in clouds: Comparisons of several models
    • doi:10.1029/2002JD002697
    • Kreidenweis,,S. M., C. J. Walcek, G. Feingold, W. Gong, M. Z. Jacobson, C. Kim, X. Liu, J. E. Penner, A. Nenes, and J. H. Seinfeld (2003), Modification of aerosol mass and size distribution due to aqueous-phase SO2 oxidation in clouds: Comparisons of several models, J. Geophys. Res., 108(D7), 4213, doi:10.1029/2002JD002697.
    • (2003) J. Geophys. Res , vol.108 , Issue.D7 , pp. 4213
    • Kreidenweis, S.M.1    Walcek, C.J.2    Feingold, G.3    Gong, W.4    Jacobson, M.Z.5    Kim, C.6    Liu, X.7    Penner, J.E.8    Nenes, A.9    Seinfeld, J.H.10
  • 21
    • 50049094263 scopus 로고    scopus 로고
    • Exploring single-particle heterogeneous chemistry of aerosols using SEM, CCSEM, ESEM and TOF-SIMS analytical techniques
    • edited by G. D. Roy, S. M. Frolov, and A. M. Starik, pp, Torus, Moscow
    • Laskin, A., D. J. Gaspar, M. J. Iedema, and J. P. Cowin (2003), Exploring single-particle heterogeneous chemistry of aerosols using SEM, CCSEM, ESEM and TOF-SIMS analytical techniques, in Combustion and Atmospheric Pollution, edited by G. D. Roy, S. M. Frolov, and A. M. Starik, pp. 565-569, Torus, Moscow.
    • (2003) Combustion and Atmospheric Pollution , pp. 565-569
    • Laskin, A.1    Gaspar, D.J.2    Iedema, M.J.3    Cowin, J.P.4
  • 22
    • 0742270203 scopus 로고    scopus 로고
    • Individual aerosol particles from biomass burning in southern Africa: 2. Compositions and aging of inorganic particles
    • doi:10.1029/2002JD002310
    • Li, J., M. Pósfai, P. V. Hobbs, and P. R. Buseck (2003), Individual aerosol particles from biomass burning in southern Africa: 2. Compositions and aging of inorganic particles, J. Geophys. Res., 108(D13), 8484, doi:10.1029/2002JD002310.
    • (2003) J. Geophys. Res , vol.108 , Issue.D13 , pp. 8484
    • Li, J.1    Pósfai, M.2    Hobbs, P.V.3    Buseck, P.R.4
  • 23
    • 0008413368 scopus 로고    scopus 로고
    • Real-time monitoring of pyrotechnically derived aerosol particles in the troposphere
    • doi:10.1021 /ac9612988
    • Liu, D. Y, D. Rutherford, M. Kinsey, and K. A. Prather (1997), Real-time monitoring of pyrotechnically derived aerosol particles in the troposphere, Anal. Chem., 69(10), 1808-1814, doi:10.1021 /ac9612988.
    • (1997) Anal. Chem , vol.69 , Issue.10 , pp. 1808-1814
    • Liu, D.Y.1    Rutherford, D.2    Kinsey, M.3    Prather, K.A.4
  • 24
    • 0031106494 scopus 로고    scopus 로고
    • Particle growth in high-speed particle beam inlets
    • doi:10.1016/S0021-8502(96)00435-1
    • Mallina, R. V., A. S. Wexler, and M. V. Johnston (1997), Particle growth in high-speed particle beam inlets, J. Aerosol Sci., 28(2), 223-238, doi:10.1016/S0021-8502(96)00435-1.
    • (1997) J. Aerosol Sci , vol.28 , Issue.2 , pp. 223-238
    • Mallina, R.V.1    Wexler, A.S.2    Johnston, M.V.3
  • 25
    • 0030145688 scopus 로고    scopus 로고
    • T-matrix computations of light scattering by nonspherical particles: A review
    • doi:10.1016/0022-4073(96)00002-7
    • Mishchenko, M. I., L. D. Travis, and D. W. Mackowski (1996), T-matrix computations of light scattering by nonspherical particles: A review, J. Quant. Spectrosc. Radiat. Transfer, 55(5), 535-575, doi:10.1016/0022-4073(96)00002-7.
    • (1996) J. Quant. Spectrosc. Radiat. Transfer , vol.55 , Issue.5 , pp. 535-575
    • Mishchenko, M.I.1    Travis, L.D.2    Mackowski, D.W.3
  • 27
    • 27144433157 scopus 로고    scopus 로고
    • Extending ATOFMS measurements to include refractive index and density
    • doi:10.1021/ac0503097
    • Moffet, R. C., and K. A. Prather (2005), Extending ATOFMS measurements to include refractive index and density, Anal. Chem., 77(20), 6535-6541, doi:10.1021/ac0503097.
    • (2005) Anal. Chem , vol.77 , Issue.20 , pp. 6535-6541
    • Moffet, R.C.1    Prather, K.A.2
  • 28
    • 11344277309 scopus 로고    scopus 로고
    • Characterization of an ambient coarse particle concentrator used or human exposure studies: Aerosol size distributions, chemical composition, and concentration enrichment
    • doi:10.1080/027868290890344
    • Moffet, R. C., L. G. Shields, J. Bernsten, R. B. Devlin, and K. A. Prather (2004), Characterization of an ambient coarse particle concentrator used or human exposure studies: Aerosol size distributions, chemical composition, and concentration enrichment, Aerosol Sci. Technol., 38(11), 1123-1137, doi:10.1080/027868290890344.
    • (2004) Aerosol Sci. Technol , vol.38 , Issue.11 , pp. 1123-1137
    • Moffet, R.C.1    Shields, L.G.2    Bernsten, J.3    Devlin, R.B.4    Prather, K.A.5
  • 29
    • 84864498689 scopus 로고    scopus 로고
    • Measurement of ambient aerosols in northern Mexico City by single particle mass spectrometry
    • Moffet, R. C., B. de Foy, L. T. Molina, M. J. Molina, and K. A. Prather (2007), Measurement of ambient aerosols in northern Mexico City by single particle mass spectrometry, Atmos. Chem. Phys. Discuss., 7, 6413-6457.
    • (2007) Atmos. Chem. Phys. Discuss , vol.7 , pp. 6413-6457
    • Moffet, R.C.1    de Foy, B.2    Molina, L.T.3    Molina, M.J.4    Prather, K.A.5
  • 30
    • 54649084467 scopus 로고    scopus 로고
    • Characterization of aerosols containing Zn, Pb, and Cl from an industrial region of Mexico City
    • in press
    • Moffet, R. C., et al. (2008), Characterization of aerosols containing Zn, Pb, and Cl from an industrial region of Mexico City, Environ. Sci. Technol., in press.
    • (2008) Environ. Sci. Technol
    • Moffet, R.C.1
  • 31
    • 33947670449 scopus 로고    scopus 로고
    • The design of single particle laser mass spectrometers
    • doi:10.1002/ mas.20113
    • Murphy, D. M. (2007), The design of single particle laser mass spectrometers, Mass Spectrom. Rev., 26(2), 150-165, doi:10.1002/ mas.20113.
    • (2007) Mass Spectrom. Rev , vol.26 , Issue.2 , pp. 150-165
    • Murphy, D.M.1
  • 33
    • 0344393533 scopus 로고    scopus 로고
    • Particle density inferred from simultaneous optical and aerodynamic diameters sorted by composition
    • doi:10.1016/S0021-8502(03)00386-0
    • Murphy, D. M., D. J. Cziczo, P. K. Hudson, M. E. Schein, and D. S. Thomson (2004), Particle density inferred from simultaneous optical and aerodynamic diameters sorted by composition, J. Aerosol Sci., 35(1), 135-139, doi:10.1016/S0021-8502(03)00386-0.
    • (2004) J. Aerosol Sci , vol.35 , Issue.1 , pp. 135-139
    • Murphy, D.M.1    Cziczo, D.J.2    Hudson, P.K.3    Schein, M.E.4    Thomson, D.S.5
  • 34
    • 33748510167 scopus 로고    scopus 로고
    • Comparison of two methods for obtaining quantitative mass concentrations from aerosol time-of-flight mass spectrometry measurements
    • doi:10.1021/ac060395q
    • Qin, X. Y., P. V. Bhave, and K. A. Prather (2006), Comparison of two methods for obtaining quantitative mass concentrations from aerosol time-of-flight mass spectrometry measurements, Anal. Chem., 78(17), 6169-6178, doi:10.1021/ac060395q.
    • (2006) Anal. Chem , vol.78 , Issue.17 , pp. 6169-6178
    • Qin, X.Y.1    Bhave, P.V.2    Prather, K.A.3
  • 35
    • 0035824399 scopus 로고    scopus 로고
    • Atmosphere - Aerosols, climate, and the hydrological cycle
    • doi:10.1126/science.1064034
    • Ramanathan, V., P. J. Crutzen, J. T. Kiehl, and D. Rosenfeld (2001), Atmosphere - Aerosols, climate, and the hydrological cycle, Science, 294(5549), 2119-2124, doi:10.1126/science.1064034.
    • (2001) Science , vol.294 , Issue.5549 , pp. 2119-2124
    • Ramanathan, V.1    Crutzen, P.J.2    Kiehl, J.T.3    Rosenfeld, D.4
  • 36
    • 30344447951 scopus 로고    scopus 로고
    • Seasonal and spatial variability of the size-resolved chemical composition of particulate matter (PM10) in the Los Angeles Basin
    • doi:10.1029/2004JD004627
    • Sardar, S. B., P. M. Fine, and C. Sioutas (2005), Seasonal and spatial variability of the size-resolved chemical composition of particulate matter (PM10) in the Los Angeles Basin, J. Geophys. Res., 110, D07S08, doi:10.1029/2004JD004627.
    • (2005) J. Geophys. Res , vol.110
    • Sardar, S.B.1    Fine, P.M.2    Sioutas, C.3
  • 37
    • 0033558244 scopus 로고    scopus 로고
    • Classification of single particles analyzed by ATOFMS using an artificial neural network, ART-2A
    • doi:10.1021/ac9809682
    • Song, X. H., P. K. Hopke, D. P. Fergenson, and K. A. Prather (1999), Classification of single particles analyzed by ATOFMS using an artificial neural network, ART-2A, Anal. Chem., 71(4), 860-865, doi:10.1021/ac9809682.
    • (1999) Anal. Chem , vol.71 , Issue.4 , pp. 860-865
    • Song, X.H.1    Hopke, P.K.2    Fergenson, D.P.3    Prather, K.A.4
  • 38
    • 33847212162 scopus 로고    scopus 로고
    • Simultaneous measurement of the effective density and chemical composition of ambient aerosol particles
    • doi:10.1021/es061425
    • Spencer, M. T., L. G. Shields, and K. A. Prather (2007), Simultaneous measurement of the effective density and chemical composition of ambient aerosol particles, Environ. Sci. Technol., 41(4), 1303-1309, doi:10.1021/es061425+.
    • (2007) Environ. Sci. Technol , vol.41 , Issue.4 , pp. 1303-1309
    • Spencer, M.T.1    Shields, L.G.2    Prather, K.A.3
  • 39
    • 0025514507 scopus 로고
    • Urban aerosol refractive-index prediction by partial molar refraction approach
    • doi:10.1021/es00081a008
    • Stelson, A. W. (1990), Urban aerosol refractive-index prediction by partial molar refraction approach, Environ. Sci. Technol., 24(11), 1676-1679, doi:10.1021/es00081a008.
    • (1990) Environ. Sci. Technol , vol.24 , Issue.11 , pp. 1676-1679
    • Stelson, A.W.1
  • 40
    • 0020002015 scopus 로고
    • Relative humidity and temperature dependence of the ammonium nitrate dissociation constant
    • doi:10.1016/0004-6981(82)90184-6
    • Stelson, A. W., and J.H. Seinfeld (1982), Relative humidity and temperature dependence of the ammonium nitrate dissociation constant, Atmos. Environ., 16(5), 983-992, doi:10.1016/0004-6981(82)90184-6.
    • (1982) Atmos. Environ , vol.16 , Issue.5 , pp. 983-992
    • Stelson, A.W.1    Seinfeld, J.H.2
  • 41
    • 0029669159 scopus 로고    scopus 로고
    • The influence on climate forcing of mineral aerosols from disturbed soils
    • doi:10.1038/380419a0
    • Tegen, I., A. A. Lacis, and I. Fung (1996), The influence on climate forcing of mineral aerosols from disturbed soils, Nature, 380(6573), 419-422, doi:10.1038/380419a0.
    • (1996) Nature , vol.380 , Issue.6573 , pp. 419-422
    • Tegen, I.1    Lacis, A.A.2    Fung, I.3
  • 42
    • 0016265165 scopus 로고
    • Pollution and planetary albedo
    • doi:10.1016/0004-6981(74)90004-3
    • Twomey, S. (1974), Pollution and planetary albedo, Atmos. Environ., 8(12), 1251-1256, doi:10.1016/0004-6981(74)90004-3.
    • (1974) Atmos. Environ , vol.8 , Issue.12 , pp. 1251-1256
    • Twomey, S.1
  • 43
    • 84876878511 scopus 로고    scopus 로고
    • Atmospheric aerosol models for systems including the ions H+, NH4+, Na+, SO42-, NO3-, Cl-, Br, and H2O
    • doi:10.1029/2001JD000451
    • Wexler, A. S., and S. L. Clegg (2002), Atmospheric aerosol models for systems including the ions H+, NH4+, Na+, SO42-, NO3-, Cl-, Br, and H2O, J. Geophys. Res., 107(D14), 4207 doi:10.1029/2001JD000451.
    • (2002) J. Geophys. Res , vol.107 , Issue.D14 , pp. 4207
    • Wexler, A.S.1    Clegg, S.L.2
  • 44
    • 33749502475 scopus 로고    scopus 로고
    • Evaporation of water from particles in the aerodynamic lens inlet: An experimental study
    • doi:10.1021/ac061184o
    • Zelenyuk, A., D. Imre, and L. A. Cuadra-Rodriguez (2006), Evaporation of water from particles in the aerodynamic lens inlet: An experimental study, Anal. Chem., 78(19), 6942-6947, doi:10.1021/ac061184o.
    • (2006) Anal. Chem , vol.78 , Issue.19 , pp. 6942-6947
    • Zelenyuk, A.1    Imre, D.2    Cuadra-Rodriguez, L.A.3


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.