Project/Cruise: DYNAMO 2011

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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 primary source was the PMEL GPS compass (Si-TEX Vector Pro), the ship gyro compass data was used when the primary data were missing.  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 Vaisala WX520 sonic anemometer that was located on the aerosol sampling mast.  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 was also 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 the PMEL Vaisala WX520 sonic anemometer. This sensor was mounted 18 meters above the sea surface on the PMEL aerosol sampling mast.  The true North and East components of the wind vector from the 6 second WX520 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, from the PMEL Vaisala WX520 sonic anemometer. This sensor was mounted 18 meters above the sea surface on the PMEL aerosol sampling mast.

Relative humidity:

One minute averages in %,  from the PMEL Vaisala WX520 sonic anemometer. This sensor was mounted 18 meters above the sea surface on the PMEL aerosol sampling mast.

Barometric Pressure:

One minute averages in units of mb,  from the PMEL Vaisala WX520 sonic anemometer. This sensor was mounted 18 meters above the sea surface on the PMEL aerosol sampling mast.


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 pumped in through an intake that was 5.3 meters below the water line.  The data data from these times is listed as "missing", -999.


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 dry the aerosol to a relative humidity (RH) of  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 (CN_Direct)and TSI 3025A (UFCN_Direct) particle counters. Another one of tubes was used to supply ambient air to a TSI3785 (UFCN_Chem) 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 12, 3 and 5 nm respectively. The total particle counts from each instrument were recorded each second. The data were filtered to eliminate periods of calibration, instrument malfunction, zero air periods and periods of obvious ship contamination from the R/V Revelle (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 primarily include data from CN_Direct and the data from CN_Stack were used to fill in periods where the CN_Direct were not available. Similarly, the UFCN values primarily include data from UFCN_Direct and the UFCN_Chem data were used to fill in periods where UFCN_Direct 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.


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. The data have been filtered to remove zero-air periods and periods of obvious ship contamination from the R/V Revelle.

PMEL Aerosol Optical Depth Data

Contact person: Trish Quinn,

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 7/2/2011 and 8/30/2011, respectively. 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 The MAN contact is Alexander Smirnov ( 

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 1 data have a "Collection Efficiency" (CE) of 1.0 applied to the four “standard” AMS measurements of sulfate, nitrate, ammonium, and organic mass for the period from the start of DYNAMO through November 29 and a CE of 0.75 for the remainder of the experiment. The CEs are based on simultaneous collection of aerosols on filters and shipboard ion chromatography analysis.

The detection limits of 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 DYNAMO were 0.04, 0.25, 0.02, and 0.31 ug/m3 for sulfate, ammonium, nitrate, and POM, respectively. Samples below these detection limits are listed as 0 in the .acf and .itx file and -8888 in the ICARTT format file. Missing data are listed as -9999 in the .acf and .ict files and NaN in the .itx file.

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.

Dynamo -- Aerosol Ion Chemistry Data

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 12 to 24 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., 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.

Gravimetrically-determined Aerosol Mass and Trace Elements

Contact persons: Tim Bates,; Trish Quinn,

A two-stage multi-jet cascade impactor sampling at 60% RH was used to determine the sub 1.1 um and 1.1-10 um diameter gravimetric aerosol mass. Millipore Fluoropore films and Teflo filters were used in the impactor. 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 Sartorius model SE2 balance, 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].

After post-experiment weighing, the Teflo filter was used to determine the PM 2.5 mass of Al, Si, Ca, Ti, and Fe using thin-film x-ray primary and secondary emission spectrometry (Feely et al, 1991; Feely et al., 1998).

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

Quinn, P.K. and D.J. Coffman, J. Geophys. Res, 103:16575-16596, 1998.
Feely et al., Geophys. Monogr. Ser., vol. 63, AGU, Washington, DC, 251 - 257, 1991.
Feely et al., Deep Sea Res., 45, 2637 - 2664, 1998.

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

Contact persons: Trish Quinn,, David Covert,, Derek Coffman,

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 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.



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.


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.


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