|
 |
|
|
ATOMIC (2019) Parameter Information
Navigation and Meteorological Measurements
Ship Position (Latitude and Longitude):
In the one minute files the position is treated somewhat differently from 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 PMEL record.
Ship 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 primary source was the PMEL GPS compass (Si-TEX Vector Pro), the ship gyro compass data were used when the primary data were missing. The 1-second data were separated into an east and north component before averaging and then recombined. NOTE: The GPS-Course is the direction the ship is moving. The GyroCompass is the direction the ship's bow is pointing. When the ship is moving at 6 or more knots they generally are 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 Vaisala WX520 sonic anemometer, located on the aerosol sampling mast. For periods of missing data, the PSD Sonic anemometer on the ship’s foremast was used. 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 in 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:
The primary source for the true wind data was the average of the PMEL Vaisala WX520 and WX536 sonic anemometers, both located on the aerosol sampling mast, 17 m above sea level. For periods of missing data the average of the ship’s two WXT sensors, located above the ship’s navigation bridge, were used. True wind speed and direction were calculated from the relative wind taking into account the ship's motion from the GPS and the ship heading from the GPS compass. The true wind vector is given as wind speed in m/s and wind direction in compass degrees (0 degrees meaning wind arriving from the north). The WindU and WindV are the east and north components of the wind vector in m/s. WindU and WindV are positive for wind going in the east and north directions..
Atmospheric Temperature:
One minute averages in degrees C. The following data sources were used. The PMEL Vaisala WXT536 and the PMEL Vaisala WXT520 sensor (both on the sampling aerosol mast at 17 m above sea level) and the NOAA PSD sensor on the bow foremast also at 17 meters above the sea surface. These 3 sensors generally agreed to better than 0.5 deg C. For this project the average of the two PMEL WXT sensors was used. During periods of missing data in the PMEL record the PSD sensor was used.
Relative humidity:
One minute averages in %. The following data sources were used. The PMEL Vaisala WXT536 and the PMEL Vaisala WXT520 sensor (both on the sampling aerosol mast at 17 m above sea level) and the NOAA PSD sensor on the bow foremast also at 17 meters above the sea surface. These 3 sensors generally agreed within 5% in rh. For this project the average of the two PMEL WXT sensors was used. During periods of missing data in the PMEL record the PSD sensor was used.
Barometric Pressure:
One minute averages in units of mb. There were two sources of raw data, the PMEL WXT sensors (corrected to sea level) and the NOAA PSD sensor (corrected to sea level). For this project the average of the sea level corrected PMEL WXT sensors was used. Missing data were filled in with the PSD sea level corrected pressure.
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 Areophys 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.
Rain Rate (Precipitation):
The rain rate, in mm/hr, was measured by the PMEL-Vaisala WX520 and WX536 Met sensors located near the top of the aerosol sampling mast. The average of the two sensors was used. During periods of high wind speed (above about 15 m/s), sea spray causes drops that will impact the rain sensor and register as rain, thus there are periods where rain is recorded when there is no rain falling. We have no way of editing this out of the data record so the measured rain rate at these higher wind speeds is unreliable.
Ozone
Air was pulled from 16 m above sea level through a 1/4 inch teflon line at approximately 1 liter min-1 into a Thermo Environmental Instruments Model 49c ozone analyzer. The air inlet was approximately 2 meters below the aerosol inlet. During periods when the relative wind was behind the beam, there were obvious periods when ship exhaust was reacting with ozone, resulting in sudden spikes of low ozone. These spikes of low ozone have been edited out. The data are reported as one minute averages in units of ppb.
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 the midpoint of the counting interval. The instrument was calibrated with a known radon source in Seattle before the cruise and a second calibration was performed after the instrument was shipped back to PMEL. Radon concentrations are given in mBq m-3.
Seawater Measurements
Sea Surface Temperature and Salinity:
Sea Surface Temperature (SST) in degrees C is from the ship’s Hull Probe (SBT38, calibrated on Sep. 17, 2019), Salinity in PSU is from the ship's SeaBird thermosalinograph (SBE 45, calibrated on Sep. 25, 2019). The temperature probe and water inlet for the thermosalinograph were located 5.3 meters below the water line. The underway chlorophyll data are from the ship’s Seapoint fluorometer, which was calibrated by the factory on Nov. 21, 2019.
Aerosol inlet:
Ambient 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 to maintain nominally isokinetic flow and minimize the loss of supermicrometer particles. Air entered the inlet through a 5 cm diameter hole, passed through a 7 degree expansion cone, and then into the 20 cm inner diameter sampling mast. The flow through the mast was 1 m3 min-1. The transmission efficiency of the inlet for particles with aerodynamic diameters less than 6.5 um (the largest size tested) is greater than 95% [Bates et al., 2002].
The bottom 1.5 m of the mast were heated to establish a stable reference relative humidity (RH) for the sample air of in the controlled range of 55 to 60 %RH. Twenty one 1.6 cm inner diameter stainless steel tubes extending into the heated portion of the mast were connected to downstream aerosol instrumentation with either conductive silicon tubing or stainless steel tubing for analysis of organic aerosol.
CN and UFCN:
One of the twenty one 1.6 cm diameter tubes was used to supply ambient air to TSI 3010 (CN_Direct), a Brechtel aMCPC (CN_Stack) and TSI 3025A (UFCN_Direct) particle counters. Another one of the tubes was used to supply ambient air to TSI3785 (UFCN_Chem) and Aerosol Devices MAGIC210 (CN_MART) particle counters. The 3010, aMCPC, 3025, 3785 and MAGIC210 measure all particles larger than roughly 12, 5, 3, 5 and 5 nm respectively. The total particle counts from each instrument were recorded each second. The data were filtered to eliminate periods of calibration and instrument malfunction and zero air periods, and periods of obvious ship contamination from the R/V Brown (based on relative wind and high CN counts). The "best" filtered values were chosen to represent CN>12 (CN) and ultra-fine (UFCN) particle concentrations. The best CN values are primarily from CN_Direct with data from CN_Stack used to fill in periods where the CN_Direct data were not available. Similarly, the UFCN values are primarily from UFCN_Direct with the UFCN_Chem and CN_MART data used to fill in periods where UFCN_Direct data were not available. These "best" data were averaged into one minute periods. One second data are available upon request. The value of -999 was assigned to any one minute period without data.
Ion Chemistry Data (Ion Chromatograph):
Two and seven-stage multi-jet cascade impactors (Berner et al., 1979) sampling air at 55-60% RH were used to determine the mass size distribution of Cl-, NO3-, SO4=, Na+, NH4+, K+, Mg+2, and Ca+2. Sampling periods ranged from 12 to 24 hours. The RH of the sampled air stream was measured a few inches upstream from the impactors. The 2-stage impactors cut the samples into submicrometer (Daero < 1.1 um at 60% RH), and supermicrometer (1.1 um < Daero < 10 um) samples. Aerosol mass size distributions from the 7-stage impactors (size cuts at: 0.18, 0.31, 0.55, 1.1, 2.0, 4.1 and 10 um) are available for download at: http://saga.pmel.noaa.gov/data/chemdist.php?cruise=ATOMIC.
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 and additional 5 ml of distilled deionized water were added to the solution and the substrates were extracted by sonicated for 30 min. For the 7 stage impactor (sizes 0.18, 0.31, 0.55 and 1.1), the extraction volume was reduced to 0.5mL:2.5mL methanol:water in later samples (12 and 15 through 27) to increase detection. The extracts were analyzed by ion chromatography [Quinn et al., 2000]. 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.
Concentrations are reported as ug/m3 at STP (25C and 1 atm). Values below the detection limit are denoted with a -8888 in the .acf file or zero in the .itx and .ict files, missing data are denoted with a -9999 in the .acf and .ict files and NaN in the .itx file.
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]. The analysis was conducted by Chester LabNet in Tigard, OR. Submicron samples were collected on Teflon filters (1.0 um pore size) mounted in a Berner impactor downstream of a D50,aero 1.1 um jet plate (Berner et al., 1979). Sub 10 micron samples were collected on Teflon filters (1.0 um pore size) mounted in a Berner impactor downstream of a D50,aero 10 um jet plate. 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 12 to 24 hours. The reported Ca does not include sea salt Ca (as determined from soluble Na
concentrations and the ratio of Ca to Na in seawater). 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).
The mass concentrations of Al, Si, Ca, Fe, and Ti, the major elements in soil, were combined to calculate the concentration of dust. It was assumed that each element was present in the aerosol in its most common oxide form (Al2O3, SiO2, CaO, K2O, FeO, Fe2O3, TiO2). The measured elemental mass concentration was multiplied by the appropriate molar correction factor as follows:
[Dust] = 2.2[Al] + 2.49[Si] + 1.63[Ca] + 2.42[Fe]+1.94[Ti]
[Malm et al., 1994; Perry et al., 1997]. This equation includes a 16% correction factor to account for the presence of oxides of other elements such as K, Na, Mn, Mg, and V that are not included in the linear combination. In addition, the equation omits K from biomass burning by using Fe as a surrogate for soil K and an average K/Fe ratio of 0.6 in soil [Cahill et al., 1986].
Berner et al., Sci. Total Environ., 13, 245 - 261, 1979.
Cahill, T.A., R.A. Eldred, and P.J. Feeney, Particulate monitoring and data analysis for the National Park Service, 1982 – 1985, University of California, Davis, 1986.
Feely et al., Geophys. Monogr. Ser., vol. 63, AGU, Washington, DC, 251 - 257, 1991.
Feely et al., Deep Sea Res., 45, 2637 - 2664, 1998.
Malm, W.C., J.F. Sisler, D. Huffman, R.A. Eldred, and T.A. Cahill, Spatial and seasonal trends in particle concentration and optical extinction in the United States, J. Geophys. Res., 99, 1347-1370, 1994.
Perry, K.D., T.A. Cahill, R.A. Eldred, D.D. Dutcher, and T.E. Gill, Long-range transport of North African dust to the eastern United States, J. Geophys. Res., 102, 11225- 11238, 1997.
Organic Carbon (Sunset Laboratory thermal/optical analyzer)
Sub-1.1 um and sub-10 um samples were collected on pre-combusted quartz fiber filters using 2 and 1 stage impactors, respectively, for organic carbon (OC) and elemental carbon (EC) analysis [Bates et al., 2004]. A charcoal diffusion denuder was deployed upstream of the submicrometer impactor to remove gas phase organic species. OC and EC concentrations were determined with a Sunset Laboratory thermal/optical analyzer. Three temperature steps were used to evolve OC under O2-free conditions for quantification. The first step heated the filter to 230 Deg C; the second step heated the filter to 600 Deg C (AMS vaporizer temperature); and the final step heated the filter to 870 Deg C. After cooling the sample down to 550 Deg C, a He/O2 mixture was introduced and the sample was heated in four temperature steps to 910 Deg C to drive off EC. The transmission of light through the filter was measured to correct the observed EC for any OC that charred during the initial stages of heating. No correction was made for carbonate carbon so OC includes both organic and carbonate carbon. The percentage of carbonate carbon is unknown. Super-micrometer OC concentrations were determined by difference between submicrometer and sub-10 um impactor samples without denuders.
X-Ray Fluorescence (analyzed by CHESTER LabNet, Tigard, OR)
Sub-1.1 um and sub-10 um samples were collected on Pall PTFE Membrane Disc Filters (2 um, 47 mm) using 2 and 1 stage impactors. Filters were analyzed for total mass by gravimetric analysis at 55 +/- 5% RH. After gravimetric analysis, a subset of filters were sent to CHESTER LabNet for XRF analysis. The following elements were reported:, Al, Si, Ca, Fe, and Ti. The XRF uncertainty measurement (as derived from calibration, counting statistics, peak overlap correction, and absorption) represents the statistical range in which a measurement may fall. More detail on XRF Data interpretation can be found here. Blank levels were determined by loading an impactor with substrates but not drawing any air through it. Concentrations are reported as ug/m3 at STP (25C and 1 atm). Values below the detection limit are denoted with a -8888 in the ICARTT files, and 0 in the ACF, IGOR and CDF versions. Missing data are denoted with a -9999 in the ICARTT files or -999 or NaN.in the ACF, IGOR and CDF versions.
Aerosol in-situ Light Scattering and Absorption, Scattering and Absorption angstrom exponents, Single Scatter Albedo, and RH dependence of scattering.
A suite of instruments was used to measure aerosol light scattering and absorption. Two TSI integrating nephelometers (Model 3563) measured integrated total scattering 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 < 1.1 micrometer. When possible, both nephelometers were operated at a sensing volume RH of approximately 60%. This RH was controlled by controlling the temperature of the insulated cabinet that housed the nephelometers.
The 10 and 1.1 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. 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 80% 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.
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.
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:
Data from the Radiance Research Particle Soot Absorption Photometers, PSAPs sub1, sub10, and _lo,
are processed as follows:
The f(RH) of scattering data is processed as follows:
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 Angstrom 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 Angstrom 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 absorption 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 Angstrom exponent.
The sub 1 micron and sub 10 micron Scattering Angstrom exponents can be found on the PMEL Data Server in the SUBSCATANG and TOTSCATANG files. The sub 1 micron and sub 10 micron Absorption Angstrom 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 radiative 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
CCN Measurements:
A Droplet Measurement Technologies CCN Counter (DMT CCNC) was used to determine CCN concentrations of sub-1 um particles at supersaturations ranging from 0.1 to 0.62%. A multijet cascade impactor with a 50% aerodynamic cut-off diameter of 1.1 um was upstream of the CCNC. The sampled air was dried prior to reaching the CCNC. Details concerning the characteristics of the DMT CCN counter can be found in Roberts and Nenes [2005] and Lance et al. [2006]. The CCN counter was calibrated before and during the experiment as outlined by Lance et al. [2006]. The uncertainty associated with the CCN number concentration is estimated to be less than +/- 10% [Roberts and Nenes, 2005]. Uncertainty in the instrumental supersaturation is less than +/- 10% for the operating conditions of this experiment [Roberts and Nenes, 2005].
The data are reported in the ATOMIC_CCN_v0 files (in acf, netCDF, ICARTT and IGOR formats). The data are in 10 second time intervals and include CCN concentration (in n/cm^3), CCN/CN ratio, and Supersaturation (in %).
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.
Aerosol Number Size Distributions:
One of the 21 1.6 cm diameter tubes was used to supply ambient air to a short differential mobility particle sizer (Aitken-DMPS) and a medium differential mobility particle sizer (Accumulation-DMPS). The two DMPSs were located in a temperature-controlled box at the base of the mast. When possible the temperature was controlled such that the RH of the sample stream was maintained at 25-35% RH. The Aitken-DMPS was a University of Vienna (Reischle) short column instrument connected to a TSI 3760A particle counter operating with a positive center rod voltage to sample particles with a negative charge. Data were collected in 10 size bins from 20 to 200 nm diameter. The Aitken-DMPS operated with an aerosol flow rate of 1 L/min and a sheath air flow rate of 10 L/min. The Accumulation-DMPS was a University of Vienna (Reischle) medium column connected to a TSI 3760A particle counter operating with a positive center rod voltage to sample particles with a negative charge. Data were collected in 7 size bins from 200 to 800 nm diameter. The Accumulation-DMPS operated with an aerosol flow rate of 0.5 L/min and a sheath air flow rate of 5 L/min. The relative humidity of the sheath air for both DMPS was controlled resulting in a measurement RH in the DMPSs 25-35 %RH. \Mobility distributions were collected every 5-minutes from a mobility scan that started at even 5 minute intervals and lasted ca. 4.75 minutes.
The mobility distributions from the Aitken-DMPS, Accumulation-DMPS were inverted to a number distribution by assuming a Fuchs-Boltzman charge distribution resulted from the Kr85 charge neutralizer (Stratman, F. and A. Wiedensohler, 1997). The overlapping channels between the two instruments were eliminated in the inversion. The data were corrected for diffusional losses and size dependent counting efficiencies based on pre-ACE-2 intercalibration exercises at IfT. Data are reported in geometric diameter (micrometers) in units of dN/dlogDp (cm-3) at an RH of 30%
The same 1.6 cm diameter tube was used to supply ambient air to the APS (TSI 3321) located in the lower temperature controlled box at the base of the mast. The temperature was controlled to maintain the RH of the aerosol sample stream of 25-35 %RH.
The APS data reported here are in 34 size bins with the nominal manufacturers aerodynamic diameters ranging from 0.96 to 10.37 um. Data are reported in aerodynamic diameter (micrometers) in units of dN/dlogDp (cm-3) at an RH of 25-35 %. Additionally, modifications were made to the APS to account for the internal heating of the sample in the APS by its sheath flow and waste heat, which could reduce the measurement RH below the nominalRH. First, the sheath flow was conditioned outside the instrument case before reintroduction into the sheath and acceleration nozzle. Second, the inlet tube was insulated to reduce heating at that point. While the temperature at the APS's sensing volume was not measured during sampling, laboratory testing prior to the cruise showed a significant reduction in the internal heating. Before the modifications, the differential temperature between the inlet and the sensing volume was about 3 Deg C, but after the modifications, the same differential temperature was reduced to less than 1 Deg C.
All data were filtered to eliminate periods of calibration and instrument malfunction. The value of -999 is assigned to any period without data.
The v1 data are given in the following file types: DMPS size distributions where the sizes are geometric diameters, APS size distributions where the sizes are aerodynamic diameters, and a combined DMS/APS number size distribution (nsd) where the sizes are in geometric diameter. The APS data were converted from aerodynamic diameters to geometric diameters using densities calculated from measured chemistry. The combined mass size distribution (msd) was calculated from the number size distribution (nsd) using the same densities. All data were filtered to eliminate periods of calibration and instrument malfunction. The value of -999 is assigned to any period without data. Data are reported in units of dN or dM/dlog(base 10)Dp (cm-3) at an RH of 30%. Format: comma-delimited ASCII. Date-Time UTC, Julian Decimal Date, Lat and Lon followed by the dmps, aps size bins as described above. The first two rows of data contain the bin numbers and the midpoint diameters in micrometers of each bin, respectively.
References: Stratman, F. and A. Wiedensohler. A new data inversion algorithm for DMPS measurements. J. Aerosol Sci., 27, 339-340, 1997.
U.S.Dept of Commerce / NOAA / OAR / PMEL / Atmospheric Chemistry
Aerosol Optical Depth (AOD)
A handheld Microtops sunphotometer (Solar Light Co.) was used for the measurement of AOD at wavelengths of 380, 440, 500, 675, and 870 nm. Details about the data processing can be found at:
https://aeronet.gsfc.nasa.gov/new_web/man_data.html
-
U.S.Dept of Commerce / NOAA / OAR / PMEL / Atmospheric Chemistry