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Volumn 111, Issue 10, 2006, Pages

PM2.5 chemical composition and spatiotemporal variability during the Californian Regional PM10/PM2.5 Air Quality Study (CRPAQS)

Author keywords

[No Author keywords available]

Indexed keywords

AIR POLLUTION; AIR QUALITY; ATMOSPHERIC AEROSOLS; ATMOSPHERIC CHEMISTRY; ATMOSPHERIC COMPOSITION; TRANSPORT PROPERTIES;

EID: 33745919511     PISSN: 01480227     EISSN: None     Source Type: Journal    
DOI: 10.1029/2005JD006457     Document Type: Article
Times cited : (147)

References (67)
  • 1
    • 0034189317 scopus 로고    scopus 로고
    • Concentration and composition of atmospheric aerosols from the 1995 SEAVS experiment and a review of the closure between chemical and gravimetric measurements
    • Andrews, E., P. Saxena, S. Musarra, L. M. Hildemann, P. Koutrakis, P. H. McMurry, I. Olmez, and W. H. White (2000), Concentration and composition of atmospheric aerosols from the 1995 SEAVS experiment and a review of the closure between chemical and gravimetric measurements, J. Air Waste Manage. Assoc., 50(5), 648-664.
    • (2000) J. Air Waste Manage. Assoc. , vol.50 , Issue.5 , pp. 648-664
    • Andrews, E.1    Saxena, P.2    Musarra, S.3    Hildemann, L.M.4    Koutrakis, P.5    McMurry, P.H.6    Olmez, I.7    White, W.H.8
  • 2
    • 27944488375 scopus 로고    scopus 로고
    • Efficiency of IMPROVE network denuders for removing nitric acid
    • paper presented at Regional and Global Perspectives on Haze: Causes, Consequences and Controversies - Visibility Specialty Conference, Air and Waste Manage. Assoc., Asheville, N. C., 25-29 Oct
    • Ashbaugh, L. L., C. E. McDade, W. H. White, P. Wakabayashi, J. L. Collett, and Y. Xiao-Ying (2004), Efficiency of IMPROVE network denuders for removing nitric acid, paper presented at Regional and Global Perspectives on Haze: Causes, Consequences and Controversies - Visibility Specialty Conference, Air and Waste Manage. Assoc., Asheville, N. C., 25-29 Oct.
    • (2004)
    • Ashbaugh, L.L.1    McDade, C.E.2    White, W.H.3    Wakabayashi, P.4    Collett, J.L.5    Xiao-Ying, Y.6
  • 4
    • 0034756209 scopus 로고    scopus 로고
    • Performance evaluation of the portable MiniVol particulate matter sampler
    • Baldauf, R. W., D. D. Lane, G. A. Marotz, and R. W. Wiener (2001), Performance evaluation of the portable MiniVol particulate matter sampler, Atmos. Environ., 35, 6087-6091.
    • (2001) Atmos. Environ. , vol.35 , pp. 6087-6091
    • Baldauf, R.W.1    Lane, D.D.2    Marotz, G.A.3    Wiener, R.W.4
  • 6
    • 33745930594 scopus 로고    scopus 로고
    • Climate change emissions inventory, draft report
    • California Air Resources Board Calif. Environ. Prot. Agency Air Resour. Board, Sacramento, Calif
    • California Air Resources Board (2004), Climate change emissions inventory, draft report, Calif. Environ. Prot. Agency Air Resour. Board, Sacramento, Calif.
    • (2004)
  • 8
    • 0036745748 scopus 로고    scopus 로고
    • Origins of fine aerosol mass in the Baltimore-Washington corridor: Implications from observation, factor analysis, and ensemble air parcel back trajectories
    • Chen, L.-W. A., B. G. Doddridge, R. R. Dickerson, J. C. Chow, and R. C. Henry (2002), Origins of fine aerosol mass in the Baltimore-Washington corridor: Implications from observation, factor analysis, and ensemble air parcel back trajectories, Atmos. Environ., 36(28), 4541-4554.
    • (2002) Atmos. Environ. , vol.36 , Issue.28 , pp. 4541-4554
    • Chen, L.-W.A.1    Doddridge, B.G.2    Dickerson, R.R.3    Chow, J.C.4    Henry, R.C.5
  • 9
    • 2442687123 scopus 로고    scopus 로고
    • Modeling reflectance and transmittance of quartz-fiber filter samples containing elemental carbon particles: Implications for thermal/optical analysis
    • doi:10.1016/j.jaerosci.2003.12.005
    • Chen, L.-W. A., J. C. Chow, J. G. Watson, H. Moosmüller, and W P. Arnott (2004), Modeling reflectance and transmittance of quartz-fiber filter samples containing elemental carbon particles: Implications for thermal/optical analysis, J. Aerosol Sci., 35(6), 765-780, doi:10.1016/ j.jaerosci.2003.12.005.
    • (2004) J. Aerosol Sci. , vol.35 , Issue.6 , pp. 765-780
    • Chen, L.-W.A.1    Chow, J.C.2    Watson, J.G.3    Moosmüller, H.4    Arnott, W.P.5
  • 10
    • 0003165912 scopus 로고    scopus 로고
    • Ion chromatography in elemental analysis of airborne particles
    • edited by S. Landsberger and M. Creatchman, Gordon and Breach, New York
    • Chow, J. C., and J. G. Watson (1999), Ion chromatography in elemental analysis of airborne particles, in Elemental Analysis of Airborne Particles, vol. 1, edited by S. Landsberger and M. Creatchman, pp. 97-137, Gordon and Breach, New York.
    • (1999) Elemental Analysis of Airborne Particles , vol.1 , pp. 97-137
    • Chow, J.C.1    Watson, J.G.2
  • 11
    • 4244129470 scopus 로고    scopus 로고
    • 2.5 carbonate concentrations at regionally representative Interagency Monitoring of Protected Visual Environment sites
    • doi:10.1029/2001JD000574
    • 2.5 carbonate concentrations at regionally representative Interagency Monitoring of Protected Visual Environment sites, J. Geophys. Res., 107(D21), 8344, doi:10.1029/2001JD000574.
    • (2002) J. Geophys. Res. , vol.107 , Issue.D21 , pp. 8344
    • Chow, J.C.1    Watson, J.G.2
  • 15
    • 0027609438 scopus 로고
    • The DRI thermal/optical reflectance carbon analysis system: Description, evaluation and applications in U.S. air quality studies
    • Chow, J. C., J. G. Watson, L. C. Pritchett, W. R. Pierson, C. A. Frazier, and R. G. Purcell (1993c), The DRI thermal/optical reflectance carbon analysis system: Description, evaluation and applications in U.S. air quality studies, Atmos. Environ., Part A, 27(8), 1185-1201.
    • (1993) Atmos. Environ., Part A , vol.27 , Issue.8 , pp. 1185-1201
    • Chow, J.C.1    Watson, J.G.2    Pritchett, L.C.3    Pierson, W.R.4    Frazier, C.A.5    Purcell, R.G.6
  • 21
    • 2442717690 scopus 로고    scopus 로고
    • Equivalence of elemental carbon by thermal/optical reflectance and transmittance with different temperature protocols
    • Chow, J. C., J. G. Watson, L.-W. A. Chen, W. P. Arnott, H. Moosmüller, and K. K. Fung (2004), Equivalence of elemental carbon by thermal/optical reflectance and transmittance with different temperature protocols, Environ. Sci. Technol., 38(16), 4414-4422.
    • (2004) Environ. Sci. Technol. , vol.38 , Issue.16 , pp. 4414-4422
    • Chow, J.C.1    Watson, J.G.2    Chen, L.-W.A.3    Arnott, W.P.4    Moosmüller, H.5    Fung, K.K.6
  • 25
    • 28544443792 scopus 로고    scopus 로고
    • Particulate carbon measurements in California's San Joaquin Valley
    • Chow, J. C., J. G. Watson, D. H. Lowenthal, L.-W. A. Chen, and K. Magliano (2006b), Particulate carbon measurements in California's San Joaquin Valley, Chemosphere, 62(3), 337-348.
    • (2006) Chemosphere , vol.62 , Issue.3 , pp. 337-348
    • Chow, J.C.1    Watson, J.G.2    Lowenthal, D.H.3    Chen, L.-W.A.4    Magliano, K.5
  • 27
    • 20444414135 scopus 로고    scopus 로고
    • Determination of the organic aerosol mass to organic carbon ratio in IMPROVE samples
    • El-Zanan, H. S., D. H. Lowenthal, B. Zielinska, J. C. Chow, and N. Kumar (2005), Determination of the organic aerosol mass to organic carbon ratio in IMPROVE samples, Chemosphere, 60(4), 485-496.
    • (2005) Chemosphere , vol.60 , Issue.4 , pp. 485-496
    • El-Zanan, H.S.1    Lowenthal, D.H.2    Zielinska, B.3    Chow, J.C.4    Kumar, N.5
  • 28
    • 33751288169 scopus 로고    scopus 로고
    • Organic compounds in biomass smoke from residential wood combustion: Emissions characterization at a continental scale
    • doi:10.1029/2001JD000661
    • Fine, P. M., G. R. Cass, and B. R. T. Simoneit (2002), Organic compounds in biomass smoke from residential wood combustion: Emissions characterization at a continental scale, J. Geophys. Res., 107(D21), 8349, doi:10.1029/2001JD000661.
    • (2002) J. Geophys. Res. , vol.107 , Issue.D21 , pp. 8349
    • Fine, P.M.1    Cass, G.R.2    Simoneit, B.R.T.3
  • 29
    • 0026490474 scopus 로고
    • The relationship of the extinction coefficient distribution to wind field patterns in southern California
    • Green, M. C., R. G. Flocchini, and L. O. Myrup (1992), The relationship of the extinction coefficient distribution to wind field patterns in southern California, Atmos. Environ., Part A, 26(5), 827-840.
    • (1992) Atmos. Environ., Part A , vol.26 , Issue.5 , pp. 827-840
    • Green, M.C.1    Flocchini, R.G.2    Myrup, L.O.3
  • 30
    • 0016567919 scopus 로고
    • Gas-particle distribution factors for organic and other pollutants in the Los Angeles atmosphere
    • Grosjean, D., and S. K. Friedlander (1975), Gas-particle distribution factors for organic and other pollutants in the Los Angeles atmosphere, J. Air Pollut. Control Assoc., 25(10), 1038-1044.
    • (1975) J. Air Pollut. Control Assoc. , vol.25 , Issue.10 , pp. 1038-1044
    • Grosjean, D.1    Friedlander, S.K.2
  • 31
    • 0033037803 scopus 로고    scopus 로고
    • 2.5 arising from volatilization of particulate nitrate from Teflon filters
    • 2.5 arising from volatilization of particulate nitrate from Teflon filters, J. Air Waste Manage. Assoc., 49(6), 725-733.
    • (1999) J. Air Waste Manage. Assoc. , vol.49 , Issue.6 , pp. 725-733
    • Hering, S.V.1    Cass, G.R.2
  • 32
    • 17644422944 scopus 로고    scopus 로고
    • Water content of ambient aerosol during the Pittsburgh Air Quality Study
    • D07S10 doi:10.1029/2004JD004651
    • Khlystov, A., C. O. Stanier, S. Takahama, and S. N. Pandis (2005), Water content of ambient aerosol during the Pittsburgh Air Quality Study, J. Geophys. Res., 110(D7), D07S10, doi:10.1029/2004JD004651.
    • (2005) J. Geophys. Res. , vol.110 , Issue.D7
    • Khlystov, A.1    Stanier, C.O.2    Takahama, S.3    Pandis, S.N.4
  • 33
    • 84905353707 scopus 로고    scopus 로고
    • 2.5 Air Quality Study (CRPAQS) 1995 integrated monitoring study data analysis: Work element 2.2.2 - Meteorological representativeness and work element 2.2.3 - Fog and low clouds characteristics
    • Santa Rosa, Calif
    • 2.5 Air Quality Study (CRPAQS) 1995 integrated monitoring study data analysis: Work element 2.2.2 - Meteorological representativeness and work element 2.2.3 - Fog and low clouds characteristics, T&B Syst., Santa Rosa, Calif.
    • (1998) T&B Syst.
    • Lehrman, D.E.1    Smith, T.B.2    Knuth, W.R.3
  • 35
    • 0001967843 scopus 로고    scopus 로고
    • Chemical mass balance modeling of the 1995 Integrated Monitoring Study database
    • edited by J. C. Chow and P. Koutrakis, Air and Waste Manage. Assoc., Pittsburgh, Pa
    • 2.5: A Fine Particle Standard, edited by J. C. Chow and P. Koutrakis, pp. 824-838, Air and Waste Manage. Assoc., Pittsburgh, Pa.
    • (1998) 2.5: A Fine Particle Standard , pp. 824-838
    • Magliano, K.L.1    Ranzieri, A.J.2    Solomon, P.A.3
  • 36
    • 33745097864 scopus 로고    scopus 로고
    • Chemical mass balance modeling of data from the 1995 Integrated Monitoring Study
    • Calif. Air Resour. Board, Sacramento, Calif
    • Magliano, K. L., A. J. Ranzieri, P. A. Solomon, and J. G. Watson (1998b), Chemical mass balance modeling of data from the 1995 Integrated Monitoring Study, Calif. Air Resour. Board, Sacramento, Calif.
    • (1998)
    • Magliano, K.L.1    Ranzieri, A.J.2    Solomon, P.A.3    Watson, J.G.4
  • 38
    • 0028255755 scopus 로고
    • Spatial and seasonal trends in particle concentration and optical extinction in the United States
    • Malm, W. C., J. F. Sisler, D. Huffman, R. A. Eldred, and T. A. Cahill (1994), Spatial and seasonal trends in particle concentration and optical extinction in the United States, J. Geophys. Res., 99(D1), 1347-1370.
    • (1994) J. Geophys. Res. , vol.99 , Issue.D1 , pp. 1347-1370
    • Malm, W.C.1    Sisler, J.F.2    Huffman, D.3    Eldred, R.A.4    Cahill, T.A.5
  • 39
    • 13244261183 scopus 로고    scopus 로고
    • Hygroscopic properties of levoglucosan and related organic compounds characteristic to biomass burning aerosol particles
    • D21202 doi:10.1029/2004JD004962
    • Mochida, M., and K. Kawamura (2004), Hygroscopic properties of levoglucosan and related organic compounds characteristic to biomass burning aerosol particles, J. Geophys. Res., 109, D21202, doi:10.1029/ 2004JD004962.
    • (2004) J. Geophys. Res. , vol.109
    • Mochida, M.1    Kawamura, K.2
  • 40
    • 0035128441 scopus 로고    scopus 로고
    • Partitioning of nitrate and ammonium between the gas and particulate phases during the 1997 IMADA-AVER study in Mexico City
    • Moya, M., A. S. Ansari, and S. N. Pandis (2001), Partitioning of nitrate and ammonium between the gas and particulate phases during the 1997 IMADA-AVER study in Mexico City, Atmos. Environ., 35(10),1791-1804.
    • (2001) Atmos. Environ. , vol.35 , Issue.10 , pp. 1791-1804
    • Moya, M.1    Ansari, A.S.2    Pandis, S.N.3
  • 42
    • 0035878064 scopus 로고    scopus 로고
    • Sensitivity of particulate matter nitrate formation to precursor emissions in the California San Joaquin Valley
    • Pun, B. K., and C. Seigneur (2001), Sensitivity of particulate matter nitrate formation to precursor emissions in the California San Joaquin Valley, Environ. Sci. Technol., 35(14), 2979-2987.
    • (2001) Environ. Sci. Technol. , vol.35 , Issue.14 , pp. 2979-2987
    • Pun, B.K.1    Seigneur, C.2
  • 45
    • 0038110051 scopus 로고    scopus 로고
    • Aerosol organic-mass-to-organic-carbon ratio measurements
    • doi:10.1021/es026123w
    • Russell, L. M. (2003), Aerosol organic-mass-to-organic-carbon ratio measurements, Environ. Sci. Technol., 37(13), 2982-2987, doi:10.1021/ es026123w.
    • (2003) Environ. Sci. Technol. , vol.37 , Issue.13 , pp. 2982-2987
    • Russell, L.M.1
  • 46
    • 0023470157 scopus 로고
    • Biharmonic spline interpolation of GEOS-3 and SEASAT altimeter data
    • Sandwell, D. T. (1987), Biharmonic spline interpolation of GEOS-3 and SEASAT altimeter data, Geophys. Res. Lett., 2, 139-142.
    • (1987) Geophys. Res. Lett. , vol.2 , pp. 139-142
    • Sandwell, D.T.1
  • 47
    • 0034192279 scopus 로고    scopus 로고
    • Source apportionment of wintertime gas-phase and particle-phase air pollutants using organic compounds as tracers
    • Schauer, J. J., and G. R. Cass (2000), Source apportionment of wintertime gas-phase and particle-phase air pollutants using organic compounds as tracers, Environ. Sci. Technol., 34(9), 1821-1832.
    • (2000) Environ. Sci. Technol. , vol.34 , Issue.9 , pp. 1821-1832
    • Schauer, J.J.1    Cass, G.R.2
  • 49
    • 0036837435 scopus 로고    scopus 로고
    • Chemical characterization of sub-micron organic aerosols in the tropical trade winds of the Caribbean using gas chromatography-mass spectrometry
    • Simoneit, B. R. T. (2002), Chemical characterization of sub-micron organic aerosols in the tropical trade winds of the Caribbean using gas chromatography-mass spectrometry, Atmos. Environ., 36(33), 5259-5263.
    • (2002) Atmos. Environ. , vol.36 , Issue.33 , pp. 5259-5263
    • Simoneit, B.R.T.1
  • 51
    • 0006796527 scopus 로고
    • Long-range tracer studies in the San Joaquin Valley
    • edited by A. J. Ranzieri and P. A. Solomon, Air and Waste Manage. Assoc., Pittsburgh, Pa
    • Smith, T. B., and D. E. Lehrman (1994), Long-range tracer studies in the San Joaquin Valley, in Proceedings of Regional Photochemical Measurement and Modeling Studies, vol. 1, edited by A. J. Ranzieri and P. A. Solomon, pp. 151-165, Air and Waste Manage. Assoc., Pittsburgh, Pa.
    • (1994) Proceedings of Regional Photochemical Measurement and Modeling Studies , vol.1 , pp. 151-165
    • Smith, T.B.1    Lehrman, D.E.2
  • 52
    • 0034258054 scopus 로고    scopus 로고
    • The ammonium nitrate particle equivalent of NOx emissions for wintertime conditions in central California's San Joaquin Valley
    • Stockwell, W. R., J. G. Watson, N. F. Robinson, W. Steiner, and W. W. Sylte (2000), The ammonium nitrate particle equivalent of NOx emissions for wintertime conditions in central California's San Joaquin Valley, Atmos. Environ., 34(27), 4711-4717.
    • (2000) Atmos. Environ. , vol.34 , Issue.27 , pp. 4711-4717
    • Stockwell, W.R.1    Watson, J.G.2    Robinson, N.F.3    Steiner, W.4    Sylte, W.W.5
  • 53
    • 2442613892 scopus 로고    scopus 로고
    • Positive and negative artifacts in particulate organic carbon measurements with denuded and undenuded sampler configurations
    • Subramanian, R., A. Y. Khlystov, J. C. Cabada, and A. L. Robinson (2004), Positive and negative artifacts in particulate organic carbon measurements with denuded and undenuded sampler configurations, Aerosol Sci. Technol., 38, suppl. 1, 27-48.
    • (2004) Aerosol Sci. Technol. , vol.38 , Issue.SUPPL. 1 , pp. 27-48
    • Subramanian, R.1    Khlystov, A.Y.2    Cabada, J.C.3    Robinson, A.L.4
  • 54
    • 7044239642 scopus 로고    scopus 로고
    • Modeling the diurnal variation of nitrate during the Pittsburgh Air Quality Study
    • D16S06 doi:10.1029/2003JD004149
    • Takahama, S., A. E. Wittig, D. V. Vayenas, C. I. Davidson, and S. N. Pandis (2004), Modeling the diurnal variation of nitrate during the Pittsburgh Air Quality Study, J. Geophys. Res., 109, D16S06, doi:10.1029/ 2003JD004149.
    • (2004) J. Geophys. Res. , vol.109
    • Takahama, S.1    Wittig, A.E.2    Vayenas, D.V.3    Davidson, C.I.4    Pandis, S.N.5
  • 55
    • 0034950902 scopus 로고    scopus 로고
    • 2.5 mass concentrations: Revisiting common assumptions for estimating organic mass
    • 2.5 mass concentrations: Revisiting common assumptions for estimating organic mass, Aerosol Sci. Technol., 35(1), 602-610.
    • (2001) Aerosol Sci. Technol. , vol.35 , Issue.1 , pp. 602-610
    • Turpin, B.J.1    Lim, H.J.2
  • 56
    • 0028534065 scopus 로고
    • Investigation of organic aerosol sampling artifacts in the Los Angeles basin
    • Turpin, B. J., J. J. Huntzicker, and S. V. Hering (1994), Investigation of organic aerosol sampling artifacts in the Los Angeles basin, Atmos. Environ., 28(19), 3061-3071.
    • (1994) Atmos. Environ. , vol.28 , Issue.19 , pp. 3061-3071
    • Turpin, B.J.1    Huntzicker, J.J.2    Hering, S.V.3
  • 57
    • 0001506654 scopus 로고    scopus 로고
    • National ambient air quality standards for particulate matter: Final rule
    • U.S. Environmental Protection Agency
    • U.S. Environmental Protection Agency (1997), National ambient air quality standards for particulate matter: Final rule, Fed. Regist., 62(138), 38,651-38,701.
    • (1997) Fed. Regist. , vol.62 , Issue.138
  • 58
    • 0036006903 scopus 로고    scopus 로고
    • 2.5 episode at the Fresno, CA Supersite
    • 2.5 episode at the Fresno, CA Supersite, Atmos. Environ., 36(3), 465-475.
    • (2002) Atmos. Environ. , vol.36 , Issue.3 , pp. 465-475
    • Watson, J.G.1    Chow, J.C.2
  • 59
    • 33751272481 scopus 로고    scopus 로고
    • Comparison and evaluation of in situ and filter carbon measurements at the Fresno Supersite
    • doi:10.1029/2001JD000573
    • Watson, J. G., and J. C. Chow (2002b), Comparison and evaluation of in situ and filter carbon measurements at the Fresno Supersite, J. Geophys. Res., 107(D21), 8341, doi:10.1029/2001JD000573.
    • (2002) J. Geophys. Res. , vol.107 , Issue.D21 , pp. 8341
    • Watson, J.G.1    Chow, J.C.2
  • 61
    • 0000276089 scopus 로고
    • The measurement process: Precision, accuracy, and validity
    • 8th ed., edited by B. S. Cohen and S. V. Hering, Am. Conf. of Govt. Ind. Hyg., Cincinnati, Ohio
    • Watson, J. G., P. J. Lioy, and P. K. Mueller (1995), The measurement process: Precision, accuracy, and validity, in Air Sampling Instruments for Evaluation of Atmospheric Contaminants, 8th ed., edited by B. S. Cohen and S. V. Hering, pp. 187-194, Am. Conf. of Govt. Ind. Hyg., Cincinnati, Ohio.
    • (1995) Air Sampling Instruments for Evaluation of Atmospheric Contaminants , pp. 187-194
    • Watson, J.G.1    Lioy, P.J.2    Mueller, P.K.3
  • 65
    • 0017611792 scopus 로고
    • On the nature and origins of visibility-reducing aerosols in the Los Angeles air basin
    • White, W. H., and P. T. Roberts (1977), On the nature and origins of visibility-reducing aerosols in the Los Angeles air basin, Atmos. Environ., 11(9), 803-812.
    • (1977) Atmos. Environ. , vol.11 , Issue.9 , pp. 803-812
    • White, W.H.1    Roberts, P.T.2
  • 66
    • 0023172591 scopus 로고
    • Theoretical analysis of evaporative losses from impactor and filter deposits
    • Zhang, X. Q., and P. H. McMurry (1987), Theoretical analysis of evaporative losses from impactor and filter deposits, Atmos. Environ., 21(8), 1779-1789.
    • (1987) Atmos. Environ. , vol.21 , Issue.8 , pp. 1779-1789
    • Zhang, X.Q.1    McMurry, P.H.2
  • 67
    • 0027073279 scopus 로고
    • Evaporative losses of fine particulate nitrates during sampling
    • Zhang, X. Q., and P. H. McMurry (1992), Evaporative losses of fine particulate nitrates during sampling, Atmos. Environ., Part A, 26(18), 3305-3312.
    • (1992) Atmos. Environ. , vol.26 , Issue.18 PART A , pp. 3305-3312
    • Zhang, X.Q.1    McMurry, P.H.2


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