Project/Cruise: VOCALS 2008

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Ship's Position (Latitude and Longitude)

In the one minute files the position is treated somewhat differently then all the other data.  The position given is the ship's position at the start of the one minute 'averaging' period.  (All other data are a true average).  The PMEL GPS was the primary source, the Ship's GPS was used when there were missing data in the ship's record. 

Ship's Speed, Course and Gyro:

The ship's GPS speed in knots (Speed Over Ground) and  GPS Course in compass degrees (Course Over Ground) are the one minute averages from the GPS (the PMEL GPS as the primary source, the Ship's GPS was the secondary source).  To make the one minute averages the 1-second recorded motion vector was separated into east and north components that were averaged into one minute bins.  The one minute components were then combined into the ship Velocity Vector. 

The GyroCompass in compass degrees is the one minute average heading.  The 1-second data was separated into an east and north component before averaging and then recombining.  NOTE:  The GPS-Course is the direction the ship is moving.  The GyroCompass is direction the ships bow is pointing.  When the ship is moving at 6 or more knots they generally are almost the same.  Due to water currents, at slow speeds there can be quite a difference between the two.  When the ship is stationary, the two are totally unrelated.

Relative Wind

The primary source for the relative wind data was the PMEL "Skyvane" anemometer that was located at the top of the aerosol sampling mast. For periods of missing data from the PMEL data source the ships IMET SCS wind sensor was used.  We assume that the relative wind information is primarily used to determine periods of ship contamination, thus we are using the anemometer that is closest to the sample inlet. This anemometer also was used as an input to the algorithm that turned off the sample pumps during periods of ship contamination.)

The one second relative wind speed and direction data were separated into orthogonal components of "keel" and "beam". These components were averaged into 1 minute averages, and then recombined to relative wind vectors. Wind speed is reported meters per second and wind direction is in degrees with -90 being wind approaching the ship on the port beam, 0 degrees being wind approaching the ship directly on the bow, and +90 degrees being wind approaching the ship on the starboard beam.

Wind Components/ True Wind Speed/ True Wind Direction:

True wind speed and direction were calculated from measurements obtained with the Ships IMET wind sensor. This sensor was mounted 14 meters above the sea surface on the ship's meteorological sampling mast at the bow and should be less affected by bending of streamlines as the air moves over the ship. (The PMEL “Skyvane” was on the top of the Aero-Van and in the ‘perturbed airflow’.)  The true North and East components of the wind vector from the 10 second SCS data were calculated and then averaged into 1 minute intervals in m/s. The true wind vector was calculated from these components and is given as wind speed in m/s and wind direction in compass degrees.  The WindU and WindV are the east and north components of the wind vector (in m/s).

Atmospheric Temperature

One minute averages in degrees C. There were three possible sources, the 2 PMEL rotronics sensors (T1 and T2) and the ship's SCS IMET sensor.  The ship's IMET sensor was located on the IMET mast at the bow of the ship, the PMEL sensors were located at the top of the Aero-phys van.  The IMET sensor being located at the bow had less warming from the daytime heating of the ship deck, (and the data record did show that IMET was cooler than T1 and T2 during the afternoon, when deck heating was a max).    Therefore, the SCS IMET sensor was used as the primary source and for the few times that data were missing from SCS, the PMEL-T1 sensor was used.

Relative humidity:

There were two PMEL rotronics sensors (RH1, and RH2) and one Ship IMET sensor (on the IMET Bow mast).   Due to the daytime deck heating (see air temperatue above) the PMEL sensors showed a "dip" in RH during the afternoon, while the Ship IMET sensor did not.  Thus, the Ship IMET sensor was used as the primary sensor and the PMEL RH1 sensor was used as the secondary sensor

Barometric Pressure:

One minute averages in units of mb.  There were two sources of raw data, the PMEL Vaisala sensor and the SCS digital sensor.  They both agreed within 0.5 mb.  There were less data gaps in the ship SCS sensor it was used as the primary sensor with a few periods filled in with the PMEL sensor. 

Insolation:

One minute averages in units of watts per square meter. Total solar radiation was measured with an Epply Black and White Pyranometer (horizontal surface receiver -180, model 8-48, serial number 12946) and an Epply precision pyranometer (horizontal surface receiver -180, twin hemispheres, model PSP, serial number 133035F3) that were mounted on the top of AERO van. Both instruments were calibrated by The Epply Laboratory on October 11, 1994. There were times when the sampling mast shaded one or both sensors. There were also times when the ship's mast/bridge shaded the sensors. The shaded data have not been edited out of the 1 minute data record. The data reported here are from the model 8-48, serial number 12946 radiometer and are in watts per square meter and are the average value over the 1 minute sampling period.

Sea Surface Temperature and Salinity:

Sea Surface Temperature (SST) in degrees C  and Salinity in PSU were measured with the Ship's Thermosalinograph.   The sample seawater for scientific uses was pump in through an intake that was 5.6 meters below the water line.  There were some obvious spikes in the Raw 2 second Salinity data and these were removed before averaging to 1 minute.

PMEL Ozone:

Air was sampled from 18 m above sea level down the 20 cm ID powder-coated aluminum aerosol sampling mast (6 m) at approximately 1 m3min-1. At the base of the sampling mast a 1 Lmin-1 flow was pulled through a 0.32 cm ID, 2m long Teflon tube into a Thermo Environmental Instruments Model 49c ozone analyzer.   The data are reported as one minute averages in units of ppb

PMEL SO2

Inlet and Instrument

Air was pulled from 18 m above sea level down the 20 cm ID powder-coated aluminum aerosol sampling mast (6 m) at approximately 1 m3min-1. At the base of the sampling mast a 2.8 Lmin-1 flow was pulled through a 0.32 cm ID, 1m long Teflon tube, a Millipore Fluoropore filter (1.0-um pore size) housed in a Teflon filter holder, a Perma Pure Inc. Nafion Drier (MD-070, stainless steel, 61 cm long) and then through 2 m of Telfon tubing to the Thermo Environmental Instruments Model 43C Trace Level Pulsed Fluorescence Analyzer. The initial 1 m of tubing, filter and drier we located in the humidity controlled (25%) chamber at the base of the mast. Dry zero air (scrubbed with a charcoal trap) was run through the outside of the Nafion Drier at 2 Lmin-1. Data were recorded in 10 second averages. The data have not been filtered for periods when Ron Brown ship exhaust entered the mast.

Standardization:

Zero air was introduced into the sample line upstream of the Fluoropore filter for 10 minutes every 6 hours to establish a zero baseline. An SO2 standard was generated with a permeation tube held at 40ºC. The flow over the permeation tube, diluted to 4.6 ppb, was introduced into the sample line upstream of the Fluoropore filter for 10 minutes every 24 hours. The limit of detection for 1 min averaged data, defined as 2 times the standard deviation of the signal during the zero periods, was 150 ppt. Data below detection limit are listed as 0 in the ACF and IGOR .itx files and -8888 in the ICARTT format file.  Missing data are listed as -9999.  Uncertainties in the concentrations based on the permeation tube weight and dilution flows are <5%. 

Seawater DMS

Seawater entered the ship at the bow, 3.7 m below the ship waterline, and was pumped to the ship laboratory.  Every 30 minutes a 5 ml water sample was valved from the ship water line directly into a Teflon gas stripper.  The sample was purged with hydrogen at 80 ml/min for 5 min. DMS and other sulfur gases in the hydrogen purge gas were collected on a Tenax filled trap, held at -5 deg C.  During the sample trapping period, 6.2 pmoles of methylethyl sulfide (MES) were valved into the hydrogen stream as an internal standard.  At the end of the sampling/purge period the trap was rapidly heated to +120 deg C and the sulfur gases were desorbed from the trap, separated on a DB-1 megabore fused silica column held at 70 deg C, and quantified with a sulfur chemiluminesence detector.  Between each water sample the system analyzed either a DMS standard or a system blank.  The system was calibrated using gravimetrically calibrated DMS and MES permeation tubes.  The precision of the analysis has been shown to be ± 2% based on replicate analysis of a single water sample at 3.6 nM DMS. The automated DMS system is described in greater detail in Bates et al. (J. Geophys. Res., 103, 16369-16383, 1998; Tellus, 52B, 258-272, 2000).  The major improvements since these papers are a new automation-data system and a more reliable cold trap consisting of an electrically heated stainless steel tube embedded in an aluminum block that is cooled to -5 deg C with a thermoelectric cooling chip

PEML Radon:
The PMEL radon instrument is a "dual flow loop, two filtered radon detector". The general features of the instrument are described in Whittlestone and Zahorowski, Baseline radon detectors for shipboard use: Development and deployment in the First Aerosol Characterization Experiment (ACE1), J. Geophys. Res., 103, 16,743-16,751, 1998. The instrument response is due to radon gas, not radon daughters (all of the existing radon daughters are filtered out before entering the decay/counting tank). The instrument registers the total number of decay counts per 30 minute interval on a filter (wire screen) arising from the decay of radon in the tank.  The volume of the decay/counting tank was 905 l and the sample flow rate into and out of the tank was typically 70 l/min.   The response time of the radon instrument is limited to about 30 minutes by the radiological decay time constants of the radon daughters on the wire screen filter. Thus, the start time given in the data file is 15 minutes prior to midpoint of the counting interval.  The insrument was calibrated with a know radon source in Seattle before the instrument was shipped to Charleston.  In Charleston and in Arica the background counts were measured by turning off all flows.  It was found that the background had increased greatly during the inport in Arica, and a much larger background was subtracted from the signal for the second leg, resulting in higher noise for leg 2.

PMEL Aerosol Optical Depth Data

Contact person: Trish Quinn, patricia.k.quinn@noaa.gov

Two handheld Microtops sunphotometer (Solar Light Co.) were used with wavelengths of 380, 440, 500, 675, and 870 nm). The full angular field of view for the Microtops is 2.5 deg. The instruments have built in pressure and temperature sensors and were operated with a GPS connection to obtain position and time of the measurements. Raw signal voltages were converted to aerosol optical depths by correcting for Rayleigh scattering [Penndorf, 1957], ozone optical depth, and an air mass that accounts for the Earth's curvature [Kasten and Young, 1989]. For the Ozone correction the table from Burrows et al (1999) was used.

Units 3803 and 4080 were calibrated by NASA GSFC on 6/20/2008 and again on 3/24/2009 . Calibrations were done using a Langley plot approach [Shaw, 1983]. These data were reduced as part of NASA's Maritime Aerosol Network. The data for MAN can be found at http://aeronet.gsfc.nasa.gov/new_web/man_data.html. The MAN contact is Alexander Smirnov (Alexander.Smirnov-1@nasa.gov). The calibration coefficient for the 500 nm channel of 4080 changed by +1.7% between 6/20 and 3/20.

Measurements on the ship followed the protocol of Knobelspiesse et al. [2003]. The scan length was set to 20 so that 20 measurements are obtained during each "shot". The largest voltage of the 20 measurements is recorded which corresponds to the lowest AOD. This approach helps to eliminate erroneous measurements that result from pointing errors on a moving ship. After the experiment, a post processing algorithm was applied. This algoritm calculates a coefficient of variation for each measurement equal to the sample standard deviation divided by the sample mean. If the CoV > than 0.05, the highest AOD is removed and CoV is recalculated. This procedure is repeated until all points "pass".

3803 data are Level 2.0 cloud screened data as defined by the MAN data quality format. 4080 are level 1.0.

Burrows, J. P., Richter, A., Dehn, A., Deters, B., Himmelmann, S., Voigt, S. and Orphal J., Atmospheric remote -sensing-reference data from GOME: 2. Temperature-dependent absorption cross sections of O3 in the 231-794 nm range, JQSRT, 61, 509-517, 1999.
Kasten, F. and A. T. Young, Revised optical air mass tables and approximation formula, Applied Optics, 28, 4735 - 4738, 1989.
Knobelspiesse, K.D. et al., Sun-pointing-error correction for sea deployment of the Microptops II handheld sun photometer, J. Atmos. Ocean. Tech., 20, 767, 2003.
Penndorf, R. , Tables of refractive index for standard air and the Rayleigh scattering coefficient for the spectral region between 0.2 and 20 um and their application to atmospheric optics, J. Opt. Soc. America, 47, 176 - 182, 1957.
Shaw, G. E., Sun Photometry, Bull. Am. Met. Soc., 64, 4-9, 1983.

Aerosol Mass Spectrometer, AMS

Concentrations of submicrometer NH4+, SO4=, NO3-, and POM were measured with a Quadrupole Aerosol Mass Spectrometer (Q-AMS) (Aerodyne Research Inc., Billerica, MA, USA) [Jayne et al., 2000; Allan et al., 2003]. The species measured by the AMS are referred to as non-refractory (NR) and are defined as all chemical components that vaporize at the vaporizer temperature of 600°C. This includes most organic carbon species and inorganic species such as ammonium nitrate and ammonium sulfate salts but not mineral dust, elemental carbon, or sea salt. The ionization efficiency of the AMS was calibrated every few days with dry monodisperse NH4NO3 particles using the procedure described by Jimenez et al. [2003]. The instrument operated on a 5 min cycle with the standard AMS aerodynamic lens.

Version 0 data have a "Collection Efficiency" (CE) of 1 applied to the four “standard” AMS measurements of sulfate, nitrate, ammonium, and organic mass, based on simultaneous collection of filters for ion chromatography as reference standards (AMS SO4= vs. IC SO4= has slope of 1.09 with
r=0.94; AMS NH4+ vs. IC NH4+ has slope of 0.85, with r=0.90).  The detection limits from individual species were determined by analyzing periods in which ambient filtered air was sampled and are calculated as three times the standard deviation of the reported mass concentration during those periods. The detection limits during VOCALS were 0.02, 0.15, 0.02, and 0.16 ug/m3 for sulfate, ammonium, nitrate, and POM, respectively. Samples below these detection limits are listed as 0 in the ACF file and -8888 in the ICARTT format file.  Missing data are listed as -9999.  

The chopper on the AMS failed on 17 November 2008.  The instrument was operated without the chopper in the "open" position from 11/24/2008-12/1/2008.  Some SO4= data were recovered, although with a much higher uncertainty.  This data set can be obtained from Lelia Hawkins (lnhawkins@ucds.edu).

Jayne, J.T., D.C. Leard, X. Zhang, P. Davidovits, K.A. Smith, C.E. Kolb, and D.R. Worsnop, Development of an aerosol mass spectrometer for size and composition analysis of submicron particles, Aersol Sci. Technol., 33, 49-70, 2000.

Allan, J.D., J.L. Jimenez, P.I. Williams, M.R. Alfarra, K.N. Bower, J.T. Jayne, H. Coe, and D.R. Worsnop, Quantitative sampling using an Aerodyne aerosol mass spectrometer. Part 1: Techniques of data interpretation and error analysis, J. Geophys. Res., 108(D3), 4090, doi:10.1029/2002JD002358, 2003.

Aerosol OC/EC

Contact person: Tim Bates, tim.bates@noaa.gov

1. Inlet

Aerosol particles were sampled 18m above the sea surface through a heated mast that extended 5 m above the aerosol measurement container. The mast was capped with a cone-shaped inlet nozzle that was rotated into the relative wind to maintain nominally isokinetic flow and minimize the loss of supermicrometer particles. Air was drawn through the 5 cm diameter inlet nozzle at 1 m3 min-1 and down the 20 cm diameter mast. The lower 1.5 m of the mast were heated to dry the aerosol to a relative humidity (RH) of <60%. This allowed for constant instrumental size cuts through variations in ambient RH. Twenty three 1.9 cm diameter electrically conductive polyethylene or stainless-steel tubes extend into this heated zone to direct the air stream at flows of 30 l min-1 to the various aerosol sizing/counting instruments and impactors. The efficiency of the mast inlet is discussed in Bates et al. (JGR 2002).

2. Sample collection

Stainless-steel tubes extending from the base of the sampling mast supplied air at 30 l min-1 to each of the impactors used for organic aerosol sampling. Two-stage and one-stage multi-jet cascade impactors (Berner et al., 1979) sampling air at <60% RH were used to determine the submicrometer and sub 10 micrometer concentrations of organic carbon (OC) and elemental carbon (EC). The 50% aerodynamic cutoff diameters, D50,aero, were 1.1 and 10 mm. For the data reported here, submicrometer refers to particles with Daero < 1.1 mm at <60% RH and supermicrometer, the difference between the concentrations measured with the two impactors, refers to particles with 1.1 mm < Daero < 10 mm at <60% RH. A 47mm quartz filter (Pall Gelman Sciences, #7202, 9.62 cm2 effective sample area) was used as the stage 1 filter in these impactors. An additional quartz filter was used as the backup filter to assess sampling artifacts.

A third submicrometer impactor with two quartz filters was deployed downstream of a 32 cm long diffusion denuder that contained 16 parallel strips (30 faces) of 20.3 cm x 3 cm carbon-impregnated glass fiber (CIG) filters (Whatman-10320163) separated by ~1.6 mm. The denuder cross-sectional area was 7.45 cm2.

The quartz filters were cleaned on board ship by baking at 550C for 12 hours. The cleaned filters were stored in Al foil lined (press-fitted) petri dishes, sealed with Teflon tape, in a freezer dedicated solely to these filters. After sample collection the filters and substrates were returned to their petri dishes and stored in the freezer until analysis. All samples were analyzed on board ship.

3. Filter sample analysis

The analysis of the filter samples was done using a Sunset Laboratory thermal/optical analyzer. The instrument heated the sample converting evolved carbon to CO2 and then CH4 for analysis by a FID. The thermal program was the same as that used during ACE-Asia (Schauer et al.2003, Mader et al., 2003). Four temperature steps were used to achieve a final temperature of 870°C in He to drive off OC. After cooling the sample down to 550°C, a He/O2 mixture was introduced and the sample was heated in four temperature steps to 890ËšC to drive off elemental carbon (EC). The instrument measured the transmission of laser light through the filter to enable the separation of EC from OC that charred during the first stages of heating.

No correction has been made for carbonate carbon in these samples so OC includes both organic carbon and carbonate carbon if it was present.

4. Uncertainties

The uncertainties associated with positive and negative artifacts in the sampling of semi-volatile organic species can be substantial [Turpin et al., 1994; Turpin et al., 2000]. An effort was made to minimize and assess positive (adsorption of gas phase species) and negative (volatilization of aerosol organic species which may have resulted from the pressure drop across the impactor and filter) artifacts by using a denuder upstream of the impactor and by comparing undenuded and denuder-filter samplers. Results from these comparisons have shown that after correcting for sampling artifacts, measured OC concentrations can vary by 10% between samplers [Mader et al., 2003]. Other sources of uncertainty in the OC mass include the air volume sampled (5%), the area of the filter (5%), 2 times the standard deviation of the blanks measured over the course of the experiment (0.44 µg/cm2) which was on average 40% of the sample, and the precision of the method (5%) based on the results of Schauer et al. [2003]. The total uncertainty, calculated as the sum of the squares was 13%. Sub-micrometer OC values were always above the detection limit of 0.1 to 0.8 ug/m3 which varied with volume. Missing values are denoted with a -9999. The supermicrometer OC values are the difference between generally similar numbers. Samples where the difference was insignificant (<0.1 ug/m3) are denoted with a -8888.

Sources of uncertainty in the EC mass include the air volume sampled (5%), the area of the filter (5%), and the precision of the method (5%) based on the results of Schauer et al. [2003]. The total uncertainty, calculated as the sum of the squares was 9%. The limit of detection varied from 0.015 to 0.12 ug/m3 based on the volume sampled. Values below the detection limit are denoted with a -8888. Missing values are denoted with a -9999. The supermicrometer EC values were not above detection limit.

 5. Data reported in archive

The following OC/EC data sets are reported in the data archive:

  1. Sub-micrometer OC – data are from the denuder/impactor sampler. The back up quartz filter behind the stage 1 quartz filter was used as the blank.
  2. Sub-micrometer EC – data are the average of the two sub-micrometer impactor samplers (with and without denuders). Missing data were below the limit of detection.
  3. Super-micrometer OC – data are the difference between the sub-10 um impactor and the sub-1 um impactor. Both impactors were run without denuders. Both impactors were corrected for blanks/artifacts using the backup quartz filter behind the stage 1 quartz filter.

Bates, T.S., D.J. Coffman, D.S. Covert, and P.K. Quinn (2002). Regional marine boundary layer aerosol size distributions in the Indian, Atlantic and Pacific Oceans: A comparison of INDOEX measurements with ACE-1, ACE-2, and Aerosols99. J. Geophys. Res., 107(D19), 10.1029/2001JD001174.

Eatough, D.J., B.D. Grover, N.L. Eatough, R.A. Cary, D.F. Smith, P.K. Hopke, and W.E. Wilson, Continuous measurement of PM2.5 semi-volatile and nonvolatile organic material. Presented at the 8th International Conference on Carbonaceous Particles in the Atmosphere, September 14-16, 2004, Vienna, Austria.

Mader, B.T., J.J. Schauer, J.H. Seinfeld, R.C. Flagan, J.Z.Yu, H. Yang, Ho-Jin Lim, B.J. Turpin, J. T. Deminter, G. Heidemann, M. S. Bae, P. Quinn, T. Bates, D.J. Eatough, B.J. Huebert, T. Bertram, and S. Howell (2003). Sampling methods used for the collection of particle-phase organic and elemental carbon during ACE-Asia, Atmos. Environ., in press.

Schauer, J.J., B.T. Mader, J. T. DeMinter, G. Heidemann, M. S. Bae, J.H. Seinfeld, R.C. Flagan, R.A. Cary, D. Smith, B.J. Huebert, T. Bertram, S. Howell, J. T. Kline, P. Quinn, T. Bates, B. Turpin, H. J. Lim, J. Z. Yu, H. Yang, and M. D. Keywood (2003). ACE-Asia intercomparison of a thermal-optical method for the determination of particle-phase organic and elemental carbon, Environ. Sci. Technol., 37, 993-1001, 10.1021/es020622f.

Turpin, B.J., J.J. Huntzicker, and S.V. Hering, Investigation of organic aerosol sampling artifacts in the Los Angeles Base, Atmos. Environ., 28, 23061-3071, 1994.

Turpin, B.J., P. Saxena, and E. Andrews, Measuring and simulating particulate organics in the atmosphere: problems and prospects, Atmos. Environ., 34, 2983-3013, 2000.

Aerosol Ion Chemistry Data

Contact persons: Tim Bates, tim.bates@noaa.gov; Trish Quinn, patricia.k.quinn@noaa.gov

Two-stage multi-jet cascade impactors (Berner et al., 1979) sampling air at <60% RH were used to determine the sub- and supermicrometer concentrations of Cl-, Br-, NO3-, SO4=, methanesulfonate (MSA-), oxalate (Ox-), Na+, NH4+, K+, Mg+2, and Ca+2. Sampling periods ranged from 2 to 23 hours. The RH of the sampled air stream was measured a few inches upstream from the impactor. The 50% aerodynamic cutoff diameters, D50,aero, were 1.1 and 10 um. Submicrometer refers to particles with Daero < 1.1 um at <60% RH and supermicrometer refers to particles with 1.1 um < Daero < 10 um at <60% RH.

The impaction stage at the inlet of the impactor was coated with silicone grease to prevent the bounce of larger particles onto the downstream stages. Tedlar films were used as the collection substrate in the impaction stage and a Millipore Fluoropore filter (1.0-um pore size) was used for the backup filter. Films were cleaned in an ultrasonic bath in 10% H2O2 for 30 min, rinsed in distilled, deionized water, and dried in an NH3- and SO2-free glove box. Filters and films were wetted with 1 mL of spectral grade methanol. An additional 5 mLs of distilled deionized water were added to the solution and the substrates were extracted by sonicating for 30 min. The extracts were analyzed by ion chromatography [Quinn et al., 1998]. All handling of the substrates was done in the glove box. Blank levels were determined by loading an impactor with substrates but not drawing any air through it.

Non-sea salt sulfate concentrations were calculated from Na+ concentrations and the ratio of sulfate to sodium in seawater. Concentrations are reported as ug/m3 at STP (25C and 1 atm).  Values below the detection limit are denoted with a -8888, missing data are denoted with a -9999.

Berner et al., Sci. Total Environ., 13, 245 - 261, 1979.
Quinn et al., J. Geophys. Res., 105, 6785 - 6805, 2000.

Gravimetrically-determined Aerosol Mass

Contact persons: Tim Bates, tim.bates@noaa.gov; Trish Quinn, patricia.k.quinn@noaa.gov

Two-stage multi-jet cascade impactors (Berner et al., 1979) sampling air at <60%  RH were used to determine sub- and supermicrometer aerosol mass concentrations. The RH of the sampled air stream was measured a few inches upstream from the impactor. The 50% aerodynamic cutoff diameters, D50,aero, were 1.1 and 10 um. Submicrometer refers to particles with Daero < 1.1 um at <60% RH and supermicrometer refers to particles with 1.1 um < Daero < 10 um at <60% RH.

The impaction stage at the inlet of the impactor was coated with silicone grease to prevent the bounce of larger particles onto the downstream stages. Millipore Fluoropore films were used as the collection substrate in the impaction stage and a Millipore Fluoropore filter (1.0-um pore size) was used for the backup filter. Films were cleaned in an ultrasonic bath in 10% H2O2 for 30 min, rinsed in distilled, deionized water, and dried in an NH3- and SO2-free glove box.

Films and filters were weighed at PMEL with a Cahn Model 29 and Mettler UMT2 microbalance, respectively. The balances are housed in a glove box kept at a humidity of <60%. The resulting mass concentrations from the gravimetric analysis include the water mass that is associated with the aerosol at <60% RH.

The glove box was continually purged with room air that had passed through a scrubber of activated charcoal, potassium carbonate, and citric acid to remove gas phase organics, acids, and ammonia. Static charging, which can result in balance instabilities, was minimized by coating the walls of the glove box with a static dissipative polymer (Tech Spray, Inc.), placing an anti-static mat on the glove box floor, using anti-static gloves while handling the substrates, and exposing the substrates to a 210Po source to dissipate any charge that had built up on the substrates. Before and after sample collection, substrates were stored double-bagged with the outer bag containing citric acid to prevent absorption of gas phase ammonia. More details of the weighing procedure can be found in Quinn and Coffman [1998].

Concentrations are reported as ug/m3 at STP (25C and 1 atm). Missing data are denoted with a -9999.

Berner et al., Sci. Total Environ., 13, 245 - 261, 1979.
Quinn et al., J. Geophys. Res., 105, 6785 - 6805, 2000.

Aerosol in-situ Light Scattering and  Absorption, Scattering and Absorption angstrom exponents, Single Scatter Albedo, and RH dependence of scattering.

Contact persons: Trish Quinn, patricia.k.quinn@noaa.gov, David Covert, dcovert@u.washington.edu, Derek Coffman, derek.coffman@noaa.gov

NOAA Pacific Marine Environmental Laboratory

A suite of instruments was used to measure aerosol light scattering and absorption.  Two TSI integrating nephelometers (Model 3563) measured integrated total scattering and hemispheric backscattering at wavelengths of 450, 550, and 700nm (Anderson et al, 1996; Anderson and Ogren, 1998). Sample flow was taken from the AeroPhysics sampling van inlet.  One nephelometer (neph_sub10) always measured aerosols of aerodynamic diameter Dae < 10 micrometers; the second nephelometer (neph_sub1) measured only aerosol of aerodynamic diameter Dae < 1 micrometer.  Both nephelometers were operated at a sensing volume RH of approximately 60%.  The 10 and 1 micrometer cut-offs were made with Berner multi-jet cascade impactors.  Two Radiance Research Particle Soot Absorption Photometers were 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 for sub 10 (psap_sub10) and sub 1 (psap_sub1) micrometer aerosols at the outlet of the respective nephelometers.

On the PMEL Data Sever the ~60% RH, neph_sub10 data are in the TOTSCAT file, the ~60% RH, neph_sub1 data are in the SUBSCAT file. The psap_sub10 and psap_sub1 data are in the PSAP file.

A separate humidity controlled system measured submicrometric light scattering at two different relative humidities, approximately 25% RH and 85% RH (neph_sub1_lo and neph_sub1_hi) with two TSI integrating 3-wavelength nephelometers operated in series downstream of a Berner impactor. There are no backscattering values available from the _hi or _lo nephelometers as the backscatter shutter mode was set to "total" due to problematic backscatter shutters. Additionally, another PSAP was included in this system to measure submicrometric absorption at three wavelengths and low RH (psap_lo).  The first nephelometer measured scattering of the ~60% conditioned aerosol from the AeroPhysics sampling van inlet at approximately 25% RH after drying of the sample flow using a PermaPure, multiple-tube nafion dryer model PR-94.  Downstream of this nephelometer a humidifier was used to add water vapor to the sample flow (6 microporous teflon tubes surrounded by a heatable water-jacket).  The sample was conditioned to approximately 85% RH, scattering was measured by the second TSI neph.  Humidity was measured by using a chilled mirror dew point hygrometer downstream of the second neph.  Absorption was measured at low RH immediately upstream of the inlet of the first neph.

On the PMEL Data Sever the neph_sub1_lo data are in the SUBSCATloRH file, the neph_sub1_hi data are in the SUBSCAThiRH file.  The psap_lo data are not on the PMEL Data Server, but can be found at the ftp address at the end of this section.

DATA COLLECTION AND PROCESSING

Data from both systems were collected and processed at 1 sec resolution but are reported as 60-second averages.  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). Light absorption is box-car averaged by the instrument over a window 10-seconds wide. 

For all parameters, the bad value code is "NaN" (-9999 in the .acf fles).  Intensive parameters  are set to NaN when the extensive properties used in their calculation fell  below the measurement noise threshold.  Both extensive and intensive properties are set to NaN (-9999) 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 are p_STP=1013.2 hPa, T_STP=273.2 K.

DERIVATION OF MEAN VALUES

EXTENSIVE PARAMETERS

Data from the TSI integrating nephelometers, Neph sub10 and Neph sub1, and f(RH=low) and f(RH=high) are processed as follows:

  1. Span gas (air and CO2) calibrations were made before the field campaign using the standard TSI program. During the campaign zero (particle free air at ambient ater vapor conc.) and CO2 span checks were made at three to four day intervals.  The resulting zero offset and span factors were applied to the data.
  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. (NOTE: There are no backscattering values available from the f(RH=low) and f(RH=high) nephelometers as discussed above.)

The uncertainty of the scattering measurements from the nephelometer were calculated to be
+/- 0.718 Mm-1  for 60-sec average and +/- 0.182 Mm-1 for 10 min average at 450nm wavelength (2-sigma)
+/- 0.520 Mm-1  for 60-sec average and +/- 0.114 Mm-1 for 10 min average at 550nm wavelength (2-sigma)
+/- 0.426 Mm-1  for 60-sec average and +/- 0.086 Mm-1 for 10 min average at 700nm wavelength (2-sigma)

Data from the Radiance Research Particle Soot Absorption Photometers, PSAPs sub1, sub10, and _lo,

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

The uncertainty of the absorption measurements from the PSAP were calculated to be
+/- 0.256 Mm-1  for 60-sec average and +/- 0.100 Mm-1 for 10 min average at 467nm wavelength (2-sigma)
+/- 0.234 Mm-1  for 60-sec average and +/- 0.098 Mm-1 for 10 min average at 530nm wavelength (2-sigma)
+/- 0.210 Mm-1  for 60-sec average and +/- 0.096 Mm-1 for 10 min average at 660nm wavelength (2-sigma)

The f(RH) of scattering data is processed as follows:

  1.  Reported values of light scattering at low RH and high RH were corrected to STP.
  2.  the exponent describing the f(RH) dependence of scattering was determined using the scattering values of neph_lo_1min (fRH-optics) and neph_hi_1min (fRH-optics) and applying a linear regression of the relationship
                      log(scat_hi/scat_lo) = -gamma*log((1-fracRH_hi)/(1-fracRH_lo))
    based on the Kasten & Hanel formula
                      scat_hi=scat_lo(1-fracRH)^(-gamma) [Wang et. al.,2006]

The fRH values given on the data server (SUBFRH) are at the measured high and low RH values. The gamma factor calculated from the equation above is available upon request.

INTENSIVE PARAMETERS

The Ångström exponent for scattering at (450,550,700nm),

                        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 30-sec wide window.

The Ångström exponent for absorption at (467,530,660nm),

                      A_Blue = -log(Ba/Ga)/log(467/530)
                      A_Green = -log(Bs/Rs)/log(467/660)
                      A_Red = -log(Gs/Rs)/log(530/660)

where Ba, Ga and Ra are light absorbtion values that apply to 467, 530 and 660 nm, respectively and where these values have been smoothed by averaging over a 30-sec wide window.

The single scatter albedo of the sub-micron aerosol was calculated as follows:

SSA = Neph1_scat / (Neph1_scat + PSAP1_abs)

where light absorption values and scattering have been averaged over 60 seconds. SSA is given for 532nm, i.e. the nephelometer data was wavelength-shifted to match the PSAP wavelength using the nephelometer based Ångström exponent.

The sub 1 micron and sub 10 micron Scattering Ångström exponents can be found on the PMEL Data Server in the SUBSCATANG and TOTSCATANG files.   The sub 1 micron and sub 10 micron Absorption Ångström exponents can be found in the SUBABSANG and TOTABSANG files.  The sub 1 micron and sub 10 micron single scatter  albedo values can be found in the SUBSSA and TOTSSA files.

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

Wang et. al, Aerosol optical properties over the Northwestern Atlantic Ocean during NEAQS-ITCT 2004, and the influence of particulate matter on aerosol hygroscopicity, submitted to J. Geo. Phys. Res., 2006

U.S.Dept of Commerce / NOAA / OAR / PMEL / Atmospheric Chemistry