TITLE: Ronald H. Brown ship Aerosol in-situ extinction, scattering and absorption, coarse/fine, dry/60% RH, during NEAQS 2004 AUTHORS: Berko Sierau* (bsierau@atmos.washington.edu ph: 206-543-6674) David S. Covert (dcovert@u.washington.edu ph: 206-685 7461) Dept. of Atmospheric Science University of Washington Box 351640 Seattle, WA 98195 USA fax: 206-543-0308 * contact for questions about the data Patricia Quinn (patricia.k.quinn@noaa.gov) NOAA Pacific Marine Environmental Laboratory 7600 Sand Point Way NE Seattle, WA, USA 1.0 DATA SET OVERVIEW: Introduction: This README file contains a description of in-situ aerosol optical data acquired on board of the research vessel Ronald H. Brown during the intensive field phase of the NEAQS-2004 field project. These data are contained in files named "Inst.name_property_(t)sec_allday_v(#).txt", where: t = averaging time of data, in seconds v(#) = version of program used to generate data file (# = version number 1,2...) *NOTES: **All data files have been compressed using "zip", as indicated by the suffix ".zip" in the filenames. Time period covered: DoY 187(186) - DoY 225 of 2005 Physical location: Research Vessel Ronal H. Brown, Aero-Van 2.0 INSTRUMENT DESCRIPTION: A suite of instruments was used to measure light scattering and absorption. Two TSI, Inc. integrating nephelometers (Model 3563) measured integrated total scatter and hemispheric backscatter at 450, 550, and 700nm wavelengths (Anderson et al, 1996; Anderson and Ogren, 1998). One nephelometer ("SupermicronScattering/Neph10") always measured aerosols of aerodynamic diameter D<10micron; the second nephelometer ("SubmicronScattering/Neph1") measured only aerosol of aerodynamic diameter D<1micron. Both nephs measured at approximately 60% RH. The 10 and 1micron cut-off was accomplished by using standard berner impactors. One Radiance Research Particle Soot Absorption Photometer ('SubmicronAbsorption/PSAP1') was used to measure light absorption by aerosols at 467, 530, and 660nm (Bond et al., 1999; Virkkula et al.,2005) under 'dry' (<25% RH) conditions. Additionally, a 'dry' system measured total scatter ('OECneph', extinction ('OEC'), and absorption ('PSAP2') at RH<25%. The system includes a TSI, Inc. integrating nephelometer measuring scattering only at 550nm, a three-wavelength (467, 530, 660nm) optical extinction cell (Virkkula, 2005), and a three-wavelength Radiance Research Particle Soot Absorption Photometer (again 467, 530, and 660nm). A Condensation Particle Counter (TSI, Inc. 3010) measured total particle counts, as sampled from the nephelometers, for quality-control only. 3.0 DATA COLLECTION AND PROCESSING Data of the 'wet' system were collected at between 1 and 5 sec resolution, depending on the instrument (1 sec for PSAP, 5 sec for Neph). However, while reported at 1-5 Hz, light absorption and scattering measurements represent 60-second averages which is also the time resolution the data will be provided. Data from each instrument are corrected and adjusted as described below, allowing for derivation of extensive parameters (light scattering and absorption) and intensive parameters (single scatter albedo, Angstrom exponent). For the 60-second data files light scattering values are smoothed over a window 40-seconds wide before calculating the Angstrom exponents. Similarly, light absorption is instrument-internally smoothed over a window 10-seconds wide. The smoothed neph data are used *only* to calculate the intensive parameters; in all cases, the reported extensive parameter light scattering is un-smoothed. The Angstrom exponent is smoothed over a 40-seconds window before averaging. Data of the 'dry' system were also collected between 1 and 5 sec resolution but are reported at a 1080 sec resolution. This is due to the determination of the light extinction which is based on a 1080 sec average time. For all parameters, the bad value code is "NaN". If no data was aquired by the data aquisition system, time lacks exist in the data files. Intensive parameters are set to NaN when the extensive properties used in their calculation fell below the measurement noise threshold (v2 noise thresholds are based on former campaigns). Both extensive and intensive properties are set to NaN during certain events, such as during filter changes, instrument calibration, obvious instrument failure etc. Negative values of absorption might occur during periods of absorption signals near or in the range of the instrument noise, and are partly shifted into the negative range due to scattering correction. STP values to be adjusted to are p_STP=1013.2 hPa, T_STP=273.2 K. DERIVATION OF MEAN VALUES: EXTENSIVE PARAMETERS Data from the TSI integrating nephelometers Neph10 and Neph1, and OECneph are processed as follows: 1) Span gas (air and CO2) calibrations were made before the field campaign. However, due to problems of the Neph1 calibration shutter during the cruise several additional calibrations had to be made during the cruise to determine TSI nephelometer gain and offset calibration coefficients. This calibration correction was applied for the Neph1 scattering data in the data processing code. 2) The TSI nephelometers measure integrated light scattering into 7-170 degrees. To derive total scatter (0-180degrees) and hemispheric backscatter (90-180degrees) angular truncation correction factors were applied as recommended by Anderson and Ogren (1998). 3) Total and hemispheric backscatter were adjusted to STP. Data from the Radiance Research Particle Soot Absorption Photometers, PSAPs 1 and 2, are processed as follows: 1) Reported values of light absorption are corrected for spot size, flow rate, artifact response to scattering, and error in the manufacturer's calibration, all given by Bond et al. (1999). Except the spot size, all corrections were made after data collection, i.e. they are not integrated into the PSAP firmware. However, the PSAP's were flow-calibrated prior to the campaign, and a flow correction was applied based on routine flow checks during the cruise. 2) Light absorption is adjusted to STP Data from the Optical Extinction Cell, OEC, is processed as follows: 1) Reported relative values of light extinction were corrected to absolute extiction values by substracting zero-baseline values derived from filtered air measurements. The standard OEC measurement cylcle was 30 min (2min purge air, 8 min filtered air, 2 min purge air, 18 min sampling air). 2) Light extinction is adjusted to STP. INTENSIVE PARAMETERS The Angstrom exponent for scattering at (450,550,700nm), 'Angstrom_neph1_60sec_allday', A_Blue = -log(Bs/Gs)/log(450/550) A_Green = -log(Bs/Rs)/log(450/700) A_Red = -log(Gs/Rs)/log(550/700) where Bs, Gs and Rs are light scattering values that apply to 450, 550 and 700 nm, respectively and where these values have been smoothed by averaging over a 40-sec wide window. The single scatter albedo of the sub-micron aerosol was calculated as follows: SSA = Neph1_scat / (Neph1_scat + PSAP1_abs) were light absorption values and scattering have been averaged over a 60-sec wide window. SSA is given for 532nm, i.e. the nephelometer- data was wavelength-shifted to match the PSAP wavelength. DERIVATION OF UNCERTAINTIES: The 95% confidence interval uncertainty in the mean values are calculated/given for each extensive and intensive optical parameters. 4.0 DATA FORMAT For some variables, the average, standard deviation (std) and uncertainty of the mean (unc) are given. All values are tab-separated. All concentrations are referenced to ambient pressure and temperature (i.e. air density). All times are the UTC times refering to the starting point of the averaging period. Endpoint is +60 sec for the 'wet' system, +1080 sec for the dry system All varibles are in STP. Column numbers of each variable are given below. The units of each variable are given in square brackets. Note that the unit Mm^-1 is inverse mega-meters (i.e. scattering, absorption or extinction per 1E+6 meters travelled). The suffix .std indicates a standard deviation and .unc indicates an uncertainty: The data are from the following instruments, as indicated: PSAP1, PSAP2: 1: DATE [DoY] 2: light absorption at 467nm [Mm^-1] 3: Abs. error 4: light absorption at 530nm [Mm^-1] 5: Abs. error 6: light absorption at 660nm [Mm^-1] 7: Abs. error Neph1, Neph10 1: DATE [DoY] 2: light scattering at 450nm [Mm^-1] 3: Abs. error 4: light scattering at 550nm [Mm^-1] 5: Abs. error 4: light scattering at 700nm [Mm^-1] 6: Abs. error 7: light backscattering at 450nm [Mm^-1] 8: Abs. error 9: light backscattering at 550nm [Mm^-1] 10: Abs. error 11: light backscattering at 700nm [Mm^-1] 12: Abs. error 13: relative humidity [%] OEcneph 1: DATE [DoY] 2: light scattering at 550nm [Mm^-1] 3: Abs. error 4: relative humidity [%] OEC 1: DATE [DoY] 2: light extinction at 467nm [Mm^-1] 3: Abs. error 4: light extinction at 530nm [Mm^-1] 5: Abs. error 6: light extinction at 660nm [Mm^-1] 7: Abs. error SSA 1: DATE [DoY] 2: SSA at 532nm [] 3: Abs. error 5.0 DATA REMARKS 6.0 REFERENCES Anderson, T.L., D.S. Covert, S.F. Marshall, M. L. Laucks, R.J. Charlson, A.P. Waggoner, J.A. Ogren, R. Caldow, R. Holm, F. Quant, G. Sem, A. Wiedensohler, N.A. Ahlquist, and T.S. Bates, "Performance characteristics of a high- sensitivity, three-wavelength, total scatter/backscatter nephelometer", J. Atmos. Oceanic Technol., 13, 967-986, 1996. Anderson, T.L., and J.A. Ogren, "Determining aerosol radiatve properties using the TSI 3563 integrating nephelometer", Aerosol Sci. Technol., 29, 57-69, 1998. Bond, T.C., T.L. Anderson, and D. Campbell, "Calibration and intercomparison of filter-based measurements of visible light absorption by aerosols", Aerosol Sci. and Tech., 30, 582-600, 1999. A. Virkkula, N. C. Ahquist, D. S. Covert, P. J. Sheridan, W. P. Arnott, J. A Ogren, "A three-wavelength optical extinction cell for measuring aerosol light extinction and its application to determining absorption coefficient", Aero. Sci. and Tech., 39, 52-67, 2005 A. Virkkula, N. C. Ahquist, D. S. Covert, W. P. Arnott, P. J. Sheridan, P. K. Quinn, D. J. Coffman,"Modification, calibration and a field test of an instrument for measuring light absorption by particles", Aero. Sci. and Tech., 39, 68-83, 2005