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: email@example.com
David S Covert
University of Washington
Department of Atmospheric Science
Seattle, WA 98195
E-Mail Address: firstname.lastname@example.org
7600 Sand Point Way NE
Seattle, WA 98115
E-Mail Address: email@example.com
The data files contain particle number-size distribution measured onboard the RV Ronald H. Brown during NEAQS 2002. These are measured by an integrated system of UDMPS, DMPS and APS instrumentation and presented as two files, one from the APS and one from the dual DMPS. The two data files represent DMPS scans and APS averages over 15 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. However, modifications were made to the APS prior to the project to address the internal heating problem.
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 start time of the scan period.
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 and ultrafine differential mobility particle sizer (UDMPS) a differential mobility particle sizer (DMPS). The two DMPSs were located in a temperature-controlled box at the base of the mast. The temperature was controlled such that the RH of the sample stream was maintained at 55% RH. 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 20 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 600 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.
One of the 23 1.6 cm diameter tubes was used to supply ambient air to the APS (TSI 3320) 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 at 55%. 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 55% RH. 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 in the between the inlet and the sensing volume was about 3ºC, but after the modifications, the same differential temperature was reduced to less than 1ºC.
The APS data reported here are in 51 size bins with the nominal manufacturers aerodynamic diameters ranging from 0.542 to 20 µm. Data are reported in aerodynamic diameter (micrometers) in units of dN/dlogDp (cm-3) at an RH of 55%.
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 have been converted from aerodynamic diameters to geometric diameters using calculated densities, calculated using a thermodynamic equilibrium model (AeRho) and data from the completed chemical analysis. 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.
The data are given in three file types: DMPS size distributions where the sizes are geometric diameters, APS size distributions where the sizes are aerodynamic diameters, and the combined DMPS and APS size distributions where the sizes are geometric diameters.
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.
Quinn, P.K., and D.J. Coffman. Local closure during ACE 1: Aerosol mass concentration and scattering and backscattering coefficients. J. Geophys. Res., 103, 16,575- 16,596, 1998.
Stratman, F. and A. Wiedensohler. A new data inversion algorithm for DMPS measurements. J. Aerosol Sci., 27, 339-340, 1997.
Data can be downloaded in a tabular ASCII format (.txt) or a comma delimited format (.csv).
U.S.Dept of Commerce / NOAA / OAR / PMEL / Atmospheric Chemistry