ACE Asia 2001
NOAA RV Ron H. Brown
Aerosol Number-Size Distributions, 3 nm to 20 µm diameter
PI contact information:
Timothy S Bates
7600 Sand Point Way NE
Seattle, WA 98115
E-Mail Address: firstname.lastname@example.org
David S Covert
University of Washington
Department of Atmospheric Science
Seattle, WA 98195
E-Mail Address: email@example.com
7600 Sand Point Way NE
Seattle, WA 98115
E-Mail Address: firstname.lastname@example.org
The data files contain particle number-size distribution measured onboard the RV Ronald H. Brown during ACE Asia 2001. These are measured by an integrated system of UDMPS, DMPS and APS instrumentation and presented as three files, one from the APS, one from the dual DMPS, and one from the combinded dual DMPS and APS. The dual DMPS and APS data files represent DMPS scans and APS averages over 15 minute intervals defined in the data file and the combined DMPS/APS file represents scans averaged over 30 minute intervals defined in the data file. The measurement RH was 55% in the DMPSs. The RH in the APS was likely less than this due to internal heating but could only be estimated.
Data were inverted, edited, and analyzed by the PIs at PMEL.
Keywords: number concentration, number-size distribution, ultrafine differential mobility particle sizer, differential mobility particle sizer, aerodynamic particle sizer, UDMPS, DMPS, APS, relative humidity
Full Description of data set:
DOY is decimal day of year such that DOY 1.5 is 12 noon UTC on 1 January. The DOY values are the average of the start and stop times of the scan periods.
Latitude and Longitude:
Position of the ship at the center of the averaging period in decimal degrees from the PMEL GPS unit.
Particle number-size distributions,
[N(Dp)], aboard the RV Ronald H. Brown:
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 55% and partially dry the aerosol. Twenty three 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 23 1.6 cm diameter tubes was used to supply ambient air to an ultrafine differential mobility particle sizer (UDMPS), a differential mobility particle sizer (DMPS) and an aerodynamic particle sizer (APS, TSI model 3320). The two DMPSs were located in a humidity-controlled box (RH = 55 ± 5%) at the base of the mast. The UDMPS was a University of Vienna (Reischle) short column instrument connected to a TSI 3025 particle counter operating with a positive center rod voltage to sample particles with a negative charge. Data were collected in 17 size bins from 3 to 26 nm diameter. The UDMPS operated with an aerosol flow rate of 1 L/min and a sheath air flow rate of 10 L/min. The DMPS was a University of Vienna (Reischle) medium column connected to a TSI 3010 particle counter operating with a positive center rod voltage to sample particles with a negative charge. Data were collected in 17 size bins from 20 to 671 nm diameter. The 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 of approximately 55%. With this RH control the aerosol should not have effluoresced if it was hydrated in the atmosphere.
Mobility distributions were collected every 15-minutes from a mobility scan that started at even 15 minute intervals and lasted ca. 13 minutes.
The mobility distributions from the UDMPS, 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.
The APS was located in the lower humidity controlled box at the base of the mast. Although the APS inlet humidity was maintained at 55 ± 5% RH, internal heating of the sample in the APS by its sheath flow and waste heat may have reduced the measurement RH below 55% RH. The sheath flow was conditioned outside the instrument case before reintroduction into the sheath and acceleration nozzle but the temperature at the APS's the sensing volume was not measured. The instrumental temperature sensors near the sensing volume of the APS showed a temperature difference of about +2°C compared to the intet temperature, but the sensing volume temperature may have been more or less than this. The effect of an RH change on the large aerosol particles at this point is hard to quantify because the time for equilibration in the inlet jets is short.
Number size distributions were collected with the APS every 15-minutes averaged over ca. 13 minutes of that time to match the DMPS scan time.
The APS data reported here are in 51 size bins with the nominal manufacturers aerodynamic diameters ranging from 0.542 to 20 µm. Data were corrected for phantom counts assuming that the counts in the largest 4 channels (Dae = 16 to 20 µm ) were phantom counts and that value was subtracted from the entire APS distribution. This resulted in a Junge slope of the number distribution that was nearly constant for Dp > 5 µm and a volume concentration that varied randomly about zero for Dp > 10µm. The APS data reported in the combined dual DMPS and APS file were corrected for ultra-Stokesian conditions in the instrument jet and non-spherical shape (Wang and John, 1987; Cheng et al., 1990; Cheng et al., 1993; Wang et al., 2002) and converted to geomtetric diameters. The aerodynamic diameters were converted to geometric diameters using densities calculated with a thermodynamic equilibrium model (AeRho). AeRho uses ion chromatograph data, thermal organic analysis and XRF analysis from impactor measurements and the measured RH to determine the densities for each impactor stage (Quinn and Coffman, 1998). These calculations assume the aerosol is internally mixed. The end product is a density-size distribution for each impactor sampling period.
All 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 value of -999 is assigned to any period without data.
Format: comma-delimited ASCII. DOY (Julian Decimal Date) (UTC) Latitude (positive North, negative South) Longitude (positive East, negative West) followed by the udmps,dmps,aps size bins as described above. The first three rows of data contain the bin numbers, the midpoint diameters in nanometers of each bin and the midpoint diameters in micrometers of each bin, respectively.
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U.S.Dept of Commerce / NOAA / OAR / PMEL / Atmospheric Chemistry