Project/Cruise: TexAQS-GoMACCS 2006

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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 Ship's GPS was the primary source, the PMEL GPS was used when there were missing data in the ship's record. 

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-T2 sensor was used.

Relative humidity:
There were two PMEL rotronics sensors (RH1, and RH2) and one Ship IMET sensor (on the IMET Bow mast).  All 3 sensors agreed very well (generally within 2% RH).  The Ship IMET sensor was chosen because it was in a better location on the ship.


Barometric Pressure:
One minute averages in units of mb.  There were two sources of raw data, the PMEL Vaisala sensor the SCS digital (Vaisala) sensor.  They both agreed within 1 mb.  There were less data gaps in the ship SCS sensor so data is given 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.


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 minute average 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).


Rainfall Rate:
The rainfall rate was measured with a Scientific Technology Inc. ORG-100 Optical Precipitation Intensity Sensor. The instrument was mounted on the railing of Aero van. The dynamic range of the sensor is 0.5 to 1600 mm/h. Spikes in the signal may be associated with sea spray and/or fog. The data are reported in units of mm/hr.


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.  When the ship was in shallow water the sampling pump was turned off to prevent sediment and mud from contaminating the plumbing.  Thus, there were numerous data gaps in this record during this project.


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 (ship GPS as the primary source, the PMEL GPS as the secondary source).  To make the one minute averages the 10-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 10-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.


PMEL/UW CN and UFCN measurements:

Aerosol particles were sampled at 18 m above sea level through a heated mast. The mast extended 5 m above and forward of the aerosol measurement container. The inlet was a rotating cone-shaped nozzle that was automatically positioned into the relative wind. Air was pulled through this 5 cm diameter inlet nozzle at 1 m3 min-1 and down the 20 cm inner diameter mast. The lowest 1.5 m of the mast was heated to reduce the relative humidity (RH) to a value of not less than 60% and partially dry the aerosol. Twenty one 1.6 cm inner diameter conductive tubes extending into this heated zone were used to subsample the main air flow for the various aerosol instruments at flows of 30 l min-1.

One of the twenty one 1.6 cm diameter tubes was used to supply ambient air to TSI 3010 and TSI 3025A  particle counters. Another one of tubes was used to supply ambient air to a TSI3785 particle counter. A separate 1/4” line was used to supply air from the top of the mast directly to a TSI 3760 particle counter. The 3760, 3010, 3025 and 3785 measure all particles larger than roughly 13, 12, 3 and 5 nm respectively. The counts from the three detectors are referred to here as CN>13 (TSI3760), CN>12 (TSI3010), CN>3 (TSI3025) and CN>5 (TSI3785). The total particle counts from each instrument were recorded each second. The data were filtered to eliminate periods of calibration and instrument malfunction and periods of ship contamination (based on relative wind and high CN counts). The “best” filtered values were chosen to represent CN>13 and ultra-fine (UFCN) particle concentrations. The best CN>13 values primarily include data from CN>12 and the data from CN>13 were used to fill in periods where the CN>12 were not available. Similarly, the UFCN values primarily include data from CN>5 and the CN>3 data were used to fill in periods  where CN>5 were not available. These "best" data were averaged into one minute periods but the one second data is available upon request. The value of -999 was assigned to any one minute period without data.



Ozone:

In one minute averages in units of ppb. 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 TECO 49c ozone analyzer.  The TECO instrument was new and was using the factory calibration.  


PMEL SO
2 Measurements aboard Ronald H. Brown during TexAQS-GoMACCS 2006
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 (60%) 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.

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 5.6 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 100 ppt. Data below detection limit are listed as 0 in the ACF file 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 enters the ship at the bow, 5.6 m below the ship waterline, and is pumped to the ship laboratory at approximately 30 lpm (water residence time within the ship is < 5 min).  Every 30 minutes a 5 ml water sample is valved from the ship water line directly into a Teflon gas stripper.  The sample is purged with hydrogen at 80 ml/min for 5 min. DMS and other sulfur gases in the hydrogen purge gas are collected on a Tenax filled trap, held at -5 deg C.  During the sample trapping period, 6.2 pmoles of methylethyl sulfide (MES) are valved into the hydrogen stream as an internal standard.  At the end of the sampling/purge period the trap is rapidly heated to +120 deg C and the sulfur gases are 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 analyzes either a DMS standard or a system blank.  The system is 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 a electically heated stainless steel tube embeded in an aluminum block that is cooled to -5 deg C with a thermoelectric cooling chip.

During the TEXAQS cruise there were problems with the system that were not resolved until August 23.  No data is shown before that date.  Also, the seawater sampling system was off when the ship was in inland passage ways and shallow water, therefore the seawater DMS data during TEXAQS is very sporadic



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.  As 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 was about 13 minutes. Thus, the start time given in the data file is 15 minutes prior to the time of the start of the counting interval. . The radon detector was standardized using radon emitted from a known source during the Galveston port stop between legs 1 and 2.


Water Soluble Submicron Aerosol Organic Carbon (PILS-WSOC) :
Contact person:  Trish Quinn, Patricia.K.Quinn@noaa.gov

See Weber et al. (2001) and Orsini et al. (2003) for a description of the PILS (Particle-Into-Liquid-Sampler).
    The 15 lpm version was used in this experiment.
INLET. The common aerosol inlet (heated to maintain the sample air at 60% RH) was used to deliver aerosol to the PILS. A Berner-type impactor with a 50% aerodynamic cutoff diameter of 1.1 um was upstream of the PILS and sampled air at 60% RH. In order to maintain a 1.1 um cut off diameter, the impactor must have 30 slpm of flow at all times.  The PILS itself runs at 15 slpm with the flow controlled by a critical orifice.  To maintain 30 slpm through the impactor, a make up flow through a bypass line was added of 15 slpm. The inlet  line extending from the base of the common aerosol inlet to the PILS was made of stainless steel.  A 30 cm long diffusion denuder was downstream of the impactor and upstream of the PILS to remove  gas phase organics. The denuder contained 18 parallel strips of 20.3 cm x 2.8 cm carbon-impregnated (CIG) filters separated by 1.8 mm.

SAMPLING. Two Kloehn syringe pumps were used to deliver low-TOC water to the top of the PILS  impactor at a flow rate of 1.35 mL/min. Liquid sample flow from the PILS went  to a Sievers Model 800 Turbo Total Organic Carbon analyzer.  Two Kloehn pumps were used to deliver sample out of the PILS to the TOC analyzer at a flow rate of 1.1 mL/min. The sample was passed through a 0.5 um in-line filter  before entering the TOC analyzer in order to measure water soluble organic carbon (WSOC).   Between every 45 min to 2 hours, sample air was passed through a HEPA filter for 15 min
to remove particles and determine the measurement background.  This measurement background was subtracted from the sample air to obtain ambient WSOC concentrations. To account for dilution of the sample by  steam in the PILS, the WSOC concentration was multiplied by the following ratio:

Dilution correction = (debubbler flow+front drain flow+water flow in)/water flow in = 1.14.

UNCERTAINTIES. WSOC relative uncertainty is estimated to be between +/-5 to 10% based on the combined uncertainties associated with air and liquid flows and background variability.

The start time indicates the actual start time of sampling, not analysis. It is equal to the start time of the analysis  minus 5 minutes. The lag time of 5 minutes was determined by the time it took the signal to increase after switching the valve from blank to sample.


Aerosol Chemistry NOAA PMEL PILS-IC Chemistry Data
Contact person:  Trish Quinn, Patricia.K.Quinn@noaa.gov

See Weber et al. (2001) and Orsini et al. (2003) for a description of the PILS (Particle-Into-Liquid-Sampler).

The 15 lpm version was used in this experiment.
     INLET. The common aerosol inlet (heated to maintain the sample air at 60% RH) was used to deliver aerosol to the PILS. A Berner-type impactor with a 50% aerodynamic cutoff diameter of 1.1 um was upstream of the PILS and sampled air at 60% RH. In order to maintain a 1.1 um cut off diameter, the impactor must have 30 slpm of flow at all times.  The PILS itself runs at 15 slpm with the flow controlled by a critical orifice.To maintain  30 slpm through the impactor, a make up flow through a bypass line was added of 15 slpm.  Two denuders were located in series after the impactor and upstream of the PILS. These were
1) a URG denuder coated with sodium carbonate for the removal of gas phase acids and
2) a URG denuder coated with H3PO3 to remove gas phase bases.

     SAMPLING. Two Kloehn syringe pumps were used to deliver LiF to the top of the PILS impactor at a flow rate of 0.43 mL/min. Liquid sample flow from the PILS went simultaneously to a cation IC and an anion IC (Metrohm Compact 761 ICs). Two Kloehn pumps were used to deliver sample  out of the PILS to each chromatograph  at a flow rate of 0.21 mL/min. 500 uL sample loops were used.  To account for dilution of the sample by steam in the PILS, the IC-measured concentration was multiplied  by the following ratio:

Dilution correction = (debubbler flow+front drain flow+LiF flow)/LiF flow = 1.28.
This method, instead of using the ratio of known to measured Li, was found to be more consistent with simultaneously collected impactor samples.

     Samples were collected and analyzed every 5 min.  Ion concentrations are reported in ug/m3 at STP.

     IC ANALYSIS. Cation analysis: a Metrohm Peak C2-100 column for Na, NH4, K, Mg, Ca.  Eluent was 2.4 mM HNO3 and 1.5 mM dipicolinic acid in 10% acetonitrile at a flow rate of 1.1 mL/min. Anion analysis: a Metrosep A Supp4 250 mm x 4 mm for Cl, NO3, SO4.
Anion eluent was 3 mM NaHCO3 and 4.9 mM Na2CO3HCO3 in 5% acetone at a flow rate of 2.2 mL/min. Methrohm's packed bed suppressor was used with 80 mM H2SO4.

11/16/06: The PILS data were corrected based on linear regressions with the impactor data.
correction factors:
    so4_corr=so4/.92+.33
    nh4_corr=nh4/.71
    no3_corr=no3/.92
    na_corr=na/.92
    br_corr=br/.92
    ca_corr=ca/.92
    cl_corr=cl/.92
    k_corr=k/.92
    mg_corr=mg/.92

Aerosol Mass Spectrometer, AMS

Chemically classified and size-resolved mass loadings of sub-micron aerosol were measured using an Aerosol Mass Spectrometer (AMS) developed at Aerodyne Research, Inc., (Billerica, Massachusetts, USA) [Jayne et al, 2000; Allan et al., 2003]. The AMS measured both the mass concentrations of chemical species and the vacuum aerodynamic size (Dva) of the particles.  The vaporized species analyzed by the AMS are referred to as non-refractory (NR), and are defined as all chemical components that vaporize (<5 s) at the vaporizer temperature of ~550°C. This includes most organic carbon species and inorganic species such NH4NO3 and (NH4)xH2SO4 but does not include crustal oxides, elemental carbon, or sea salt.

Version 0 data have been corrected for collection efficiency based on aerosol acidity and size.  The aerosol acidity correction is based on the NH4/SO4 ratio and comparisons with the PILS-IC SO4 data. The size correction takes into account the reduced transmission efficiencies above 550 nm vacuum aerodynamic diameter.


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 in-situ Light Scattering and  Absorption, Scattering and Absorption angstrom exponents, Single Scatter Albedo, and RH dependence of scattering.
Berko Sierau
David S. Covert
Dept. of Atmospheric Science

University of Washington
and
Patricia Quinn (patricia.k.quinn@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 SUBSCAT) 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 83% RH (neph_sub1_lo and neph_sub1_hi) with two TSI integrating 3-wavelength nephelometers operated in series downstream of a Berner impactor.  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 initially 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 approx. 83% 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 recorded at 1 sec resolution.  However, while reported at 1 second time intervals in the files, 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 30-seconds wide before calculating the Angstrom exponents.  Light absorption is box-car averaged by the instrument over a window 10-seconds wide.  The averaged neph data are used *only* to calculate the intensive parameters; in all cases, the reported extensive parameter light scattering is not averaged.   The Angstrom exponent is smoothed over a 30-seconds window before averaging.

For all parameters, the bad value code is "NaN" (-9999 in the .acf fles).  If no data was acquired by the data aquisition system, time gaps 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 (-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.

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 thecampaign, and a flow correction was applied based on routine flow checks during the cruise.

                       2 ) Light absorption is adjusted to STP
 
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), neph_sub1_1min (RH60-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]

On the PMEL Data Server the fRH factor RH_85/RH_25 is given in the SUBFRH.  The f(RH) at the measured RH, and the gamma factor can be found in the files at the ftp address at the end of this section

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 40-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 40-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.

Full data files with uncertainties can be found at the ftp address:

ftp://ftp.atmos.washington.edu/bsierau

 

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

PMEL Aerosol Optical Depth Data

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

Three 5-channel handheld Microtops sunphotometer (Solar Light Co.) were used. Two units (SN 4080 and 3803) have wavelengths of 380, 440, 500, 675, and 870 nm). The third unit (SN 5355) has wavelengths of 340, 380, 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]. Ozone column amounts used to calculate the ozone optical depth were obtained from daily ozonesondes done onboard the ship. Units 3803 and 4080 were calibrated by Solar Light at their facility on May 12, 2006. Unit 5355 was calibrated at Solar Light on June 13, 2006. Calibrations were done using a Langley plot approach [Shaw, 1983].

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". All units were compared at each common wavlength. For 380 nm, the slope was 0.98 and r^2 was 0.99. For 500 nm, the slope was 0.99 and r^2 was 0.99. For 675 nm, the slope was 0.98 and the r^2 was 0.99. For 870 nm, the slope was 0.96 to 0.98 and the r^2 was 0.99. For 440 nm the slope was 0.99 and r^2 was 0.99. The uncertainty of the Microtops is esimated to be +/- 0.015 AOD.

REFERENCES

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.



PMEL OC/EC aerosol sampling methods for TexAQS 2006
January 19, 2007 
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 supermicron 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 ± 5%. 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 submicron and sub 10 micron 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, submicron refers to particles with Daero < 1.1 mm at 60% RH and supermicron, the difference between the concentrations measured with the two impactors, refers to particles with 1.1 mm < Daero < 10 mm at 55% 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 submicron 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 550˚C 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 890˚C 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 10% 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-micron 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 supermicron 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 supermicron EC values were not above detection limit.

 

6. Data reported in archive

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

  1. Sub-micron 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-micron EC – data are the average of the two sub-micron impactor samplers (with and without denuders). Missing data were below the limit of detection.
  3. Super-micron 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.


NOAA PMEL Aerosol Chemistry Data - collected with 2 stage impactors

Contact persons: Trish Quinn, patricia.k.quinn@noaa.gov; Kristen Schulz, Kristen.schulz@noaa.gov

Two-stage multi-jet cascade impactors (Berner et al., 1979) sampling air at 55 ± 5% RH were used to determine the sub- and supermicron concentrations of Cl-, Br-, NO3-, SO4=, methanesulfonate (MSA-), oxalate (Ox-), Na+, NH4+, K+, Mg+2, and Ca+2. Sampling periods ranged from 2 to 14 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. Submicron refers to particles with Daero < 1.1 um at 55% RH and supermicron refers to particles with 1.1 um < Daero < 10 um at 55% 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).

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

 


NOAA PMEL Gravimetrically-determined Aerosol Mass - collected with 2 stage impactors

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

Two-stage multi-jet cascade impactors (Berner et al., 1979) sampling air at 55 ± 5% RH were used to determine sub- and supermicron 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. Submicron refers to particles with Daero < 1.1 um at 55% RH and supermicron refers to particles with 1.1 um < Daero < 10 um at 55% 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 65 ± 4%. The resulting mass concentrations from the gravimetric analysis include the water mass that is associated with the aerosol at 65% 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).

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

 


Aerosol Trace Elements Data :

     Concentrations of Al, Si, Ca, Ti, and Fe were determined by thin-film x-ray primary and secondary emission spectrometry [Feely et al., 1991; Feely et al., 1998].  Submicron and sub-10 um samples were collected on Teflo filters (1.0 um pore size) mounted in Berner impactors having a D50,aero of 1.1 um and 10 um jet plates,
respectively (Berner et al., 1979).  Supermicron elemental concentrations were determined by difference between the submicron and sub-10 um concentrations.  This method of sample collection allows for the sharp size cut of the impactor while collecting a thin film of aerosol necessary for the x-ray analysis.  Sampling periods ranged from 2 to 14 hours.
     Blank levels were determined by loading an impactor or filter pack with a filter but not drawing any air through it.
     Concentrations are reported as ug/m3 at STP (25C and 1 atm).
Berner et al., Sci. Total Environ., 13,  245 - 261, 1979.
Feely et al., Geophys. Monogr. Ser., vol. 63, AGU, Washington, DC, 251 - 257, 1991.
Feely et al., Deep Sea Res., 45, 2637 - 2664, 1998.

Cloud Condensation Nuclei

A Droplet Measurement Technologies (DMT) CCN counter was used to determine CCN concentrations at supersaturations, S, of 0.22, 0.44, 0.65, 0.84, and 1.0%. Details concerning the characteristics of the DMT CCN counter can be found in Roberts and Nenes [2005] and Lance et al. [2006]. A multijet cascade impactor [Berner et al., 1979] with a 50% aerodynamic cutoff diameter of 1 µm was upstream of the CCN counter. The instrument was operated in two different modes. When the ship was located close to urban, industrial, or marine vessel sources such that aerosol concentrations fluctuated rapidly, a single supersaturation setting of 0.44% was often used. Away from sources when aerosol conditions were more stable, the five different supersaturations were cycled through over a 30 min period. For the multiple supersaturation mode, the first 2 min of each 6 min period were discarded so that only periods with stable supersaturations are included in the analyzed data set.

The CCN counter was calibrated before and during the experiment as outlined by Lance et al. [2006]. An (NH4)2SO4 aqueous solution was atomized with dry air, passed through a diffusional drier, diluted and then introduced to a Scanning Mobility Particle Sizer (SMPS, TSI). The resulting monodisperse aerosol stream was sampled simultaneously by the CCN counter and a water-based Condensation Particle Counter (WCPC, TSI) in order to determine the average activated fraction (CCN/CN). This procedure was repeated for a range of particle sizes and instrumental supersaturations. Using this procedure, the instrument supersaturation is equal to the critical supersaturation of the particle obtained from the activation curve for an activated fraction of 50%. The critical supersaturation for a given particle size was calculated from Köhler theory (e.g., Fitzgerald and Hoppel, 1984). The supersaturations reported in the text are based on the calibrations and not the instrumental readout which disregards thermal efficiency. The difference between the calibrated values and those reported by the instrument were similar to the difference found by Lance et al. [2006]. The uncertainty associated with the CCN number concentrations is estimated to be less than ± 10% [Roberts and Nenes, 2005]. Uncertainty in the instrumental supersaturation is less than ± 1% for the operating conditions of this experiment [Roberts and Nenes, 2005]. Data are reported as 5 min averaged values.

Bates, T.S., D.J. Coffman, D.S. Covert, and P.K. Quinn, 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, 2002.

Berner, A., C. Lurzer, F. Pohl, O. Preining, and P. Wagner, The size distribution of the urban aerosol in Vienna, Sci. Total Environ., 13, 245 – 261, 1979.

Fitzgerald, J.W. and W.A. Hoppel, Equilibrium size of atmospheric aerosol particles as a function of relative humidity: Calculations based on measured aerosol properties, in Hygroscopic Aerosols, edited by L.H. Ruhnke and A. Deepak, pp. 21 – 34, A. Deepak, Hampton, VA, 1984.

Lance, S., J. Medina, J.N. Smith, and A. Nenes, Mapping the operation of the DMT continuous flow CCN counter, Aer. Sci. Tech., 40, 242 – 254, 2006.

Roberts, G.C. and A. Nenes, A continuous-flow streamwise thermal gradient CCN chamber for atmospheric measurements, Aer. Sci. Tech., 39, 206 – 221, 2005.


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