ACE-1 H-TDMA data on aerosol particle hygroscopic growth ------------------------------------------------------------------------------- PI: Dr. Erik Swietlicki Operators: M.Sc. Olle Berg (Leg-2), M.Sc. Radovan Krejci (Leg-1) Affiliation: Dept. of Nuclear Physics, Lund University, Lund, Sweden Operation platform: NOAA R/V Discoverer (Aerosol container) Instrumentation: Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) Size range: 20-165 nm dry (<10%RH) particle diameter Primary parameters measured: 1) Diameter growth factor (from <10% to 90 % RH) of individual particles 2) Diameter growth dispersion factor 3) Relative fraction of particles in each hygroscopic mode ------------------------------------------------------------------------------- >Description of instrument Measurements of aerosol particle hygroscopic growth were performed with a Hygroscopic Tandem Differential Mobility Analyser (H-TDMA). This instrument determines, in situ, the hygroscopic diameter growth of individual aerosol particles when taken from a dry (<10% relative humidity; RH) to a controlled humidified state. The TDMA consists mainly of three parts; (1) a Differential Mobility Analyser (DMA) which selects a narrow particle size range, a quasi-monodisperse aerosol, of the sampled submicrometer atmospheric aerosol, (2) humidifiers which condition the air to a well-defined RH (during ACE-1 to 50 or 90% RH) and (3) a second DMA which determines the change in diameter caused by the humidification. >Humidification The sheath air and the aerosol entering DMA2 were humidified separately. During normal operation, the sheath air humidification was set to control at 90% RH while the aerosol was controlled at 85% RH. This ensured that no accidental deliquescence occurred in the aerosol line before entering DMA2. The RH of the excess air exiting DMA2 was continuously measured with a dew point hygrometer. This is the RH value given in the data compilation. >Mode of operation Every 6 hours, one hour was spent measuring hygroscopic growth at 50% RH. The purpose of the measurements at 50% RH is to calculate dry mass size distributions from the impactor data. The impactors were operated at 50% RH to reduce bounce-off problems. During the 50% RH measurements, the sheath air humidification was set to control at 50% RH while the aerosol was controlled at 90% RH. This ensured that the aerosol particles entering DMA2 had experienced a high RH before measuring the growth factor from a dry state to 50% RH, thus mimicking the RH history of the particles as they flow down the heated aerosol inlet and into the impactors. Particles showing RH hysteresis behaviour (such as e.g. pure NaCl) will therefore be measured in the metastable condition where the solution is supersaturated with respect to the salt in question. >Calibration The DMAs were calibrated in the DMA calibration workshop at Ift, Leipzig, Germany in June 1995. The CPCs were calibrated in the CPC calibration workshop in Seattle in August 1995. The RH sensors were calibrated against the dew point hygrometer. >Use of primary data The primary data (diameter growth factor, diameter growth dispersion factor, relative fraction of particles in each hygroscopic mode) can be used to estimate other secondary parameters such as the volume fraction of soluble/insoluble material in individual particles. The aerosol particle size at ambient RH can be calculated by combining H-TDMA data with dry aerosol size distribution (DMPS) data and size- resolved (cascade impactor) data on aerosol ionic composition. H-TDMA data can also be used to extrapolate the ambient size distribution to water vapour supersaturation and thus calculate CCN spectra. >Data files: All the *.csv files are SEMICOLON delimited and can be imported into Excel as such. Make sure you set your list separator to semicolon before importing. (e.g. in Windows95: Control Panel/Regional Settings/List Separator: choose semicolon) The files covers both leg 1 and 2 of R/V Discoverer's cruise. Route: Seattle (USA) - Hobart (Australia) - Hobart (Australia) Dates: 15 Oct. 1995 - 13 Dec. 1995 The files are: L1_35NM.CSV L1_50NM.CSV L1_75NM.CSV L1_165NM.CSV L1_50RH.CSV L2_35NM.CSV L2_50NM.CSV L2_150NM.CSV L2_50RH.CSV The files L1_35NM.CSV, L1_50NM.CSV, L1_75NM.CSV and L1_165NM.CSV contain the H-TDMA measurements performed at 90% RH during Leg-1 for the dry sizes 35, 50, 75 and 165 nm respectively. The file L1_50RH.CSV contains the H-TDMA measurements performed at 50% RH during Leg-1. The files L2_35NM.CSV, L2_50NM.CSV, and L2_150NM.CSV contain the H-TDMA measurements performed at 90% RH during Leg-2 for the dry sizes 35, 50, and 150 nm respectively. The file L2_50RH.CSV contains the H-TDMA measurements performed at 50% RH during Leg-2 for the dry sizes 50 and 150 nm. The columns of these data files are arranged in the following order (there are some small differences between leg-1 and leg-2): Date (year-month-day), Time (Julian date.fraction, UTC), DMA2 RH (actual relative humidity at which growth factors were observed), Julian date, Run no. (can be used as a data reference), Dry size (quasi-monodisperse dry aerosol mean diameter exiting DMA 1), 1st hygroscopic peak parameters Growth factor (mean ratio of humidified diameter to dry diameter), Aerosol fraction (fraction of particles with the measured growth factor), Beta factor (ratio of measured to expected mobility distribution width), Growth dispersion factor (variation in growth factor) The same parameters are included for 2nd or 3rd peaks, if they were observed. Finally, latitude and longitude is given for every scan during Leg-1. The growth factors are assumed to be normally distributed with an arithmetic mean given by the growth factor value and the standard deviation given by the growth factor value multiplied with the value of the growth dispersion factor. >Quality control All data presented was quality assured and fulfilled a number of criteria based mainly on temperature and relative humidity stability in DMA2 and influence from ship's pollution. >Use of data All researchers within the ACE-1 community are welcome and even encouraged to use this data. Please inform the Lund PI (address below) before the data is used. The Lund group requests to be (at least) acknowledged in any publication, report or presentation using these data. For additional information contact: ========================================================================= Dr. Erik Swietlicki Tel: +46 (46) 222 96 80 Department of Nuclear Physics Fax: +46 (46) 222 47 09 LTH, Box 118 Fax (on PC): +46 (46) 222 76 29 S-221 00 Lund Sweden e-mail:ERIK.SWIETLICKI@PIXE.LTH.SE (MIME) WWW-page: http://www.fysik.lu.se/~eriksw/ =========================================================================