Readme file for Huebert Group cascade impactor chemical data:

We operated 8-stage Micro-Orifice Uniform Deposit Impactors (MOUDIs) at Cape Grim during the ACE-1 project.  They were connected to the 10m inlet used by several other investigators.  It heated entering air to reduce the relative humidity to approximately 50%.

Samples were generally changed daily, though not on a fixed schedule.  Some effort was taken to coordinate sample times with meteorological changes.  Sampling was continuous, whether or not baseline conditions existed.

In addition to the 8 impaction stages, we also analyzed the inlet stage and a backup filter.  Impaction substrates were aluminum foil, while the backup filters were Millipore FALP (polytetrafluoroethylene) with 1 micron nominal pore size.  Ion chromatography was used to analyze samples for sodium, ammonium, potassium, magnesium, calcium, methanesulfonate, chloride, nitrate, and sulfate.

The design flow rate for the MOUDI is 30 liters per minute.  Nominal cut diameters of the MOUDI stages are:

Stage    50% cut (aerodynamic diameter, microns)
----------------
inlet      15     (though the 10 m inlet efficiency is not known)
  1        10.
  2         5.6
  3         3.2
  4         1.8
  5         1.0
  6         0.56
  7         0.32
  8         0.18
filter      not well defined, though very small.  We assume 0.10 microns
            for plotting purposes only, as little mass is present below
            that size.

Aerodynamic diameter is defined as the size of a particle with unit density (1g/ml) with the same aerodynamic behavior (Stokes number) as a sampled particle.  For particles > 0.1 micron or so, this works out to approximately

diameter = aerodynamic diameter / sqrt(particle density).

Flow rates were not always 30 lpm, so the data file indicates corrected size cuts, determined by using

cut = nominal cut * sqrt(nominal flow/actual flow).

File format:

The data file is ASCII text.  Fields are separated with tab characters.

There are two header lines.  The first names each column, while the second gives units.

The columns are:
1)  Sample name.  This is included primarily to make it clear which substrates
    were exposed together in the same sample.
2)  Beginning day for the sample (day of year)
3)  Beginning time, HHMM  (local time, not UTC or station time)
4)  Ending day for the sample (day of year)
5)  Ending time, HHMM  (local time)
6)  Impactor stage (0 for inlet, 1-8, F for after-filter)
7)  50% cut size for the stage, corrected for flow rate (aerodynamic 
    diameter, microns).  As a very rough first approximation, one can assume 
    that each stage captures all particles larger than its size cut and smaller 
    than that of the previous stage.
8-16) Concentration of ions, reported as picomoles of ion captured on the stage 
    per mole of sampled air.
17-18) Non-seasalt sulfate, calculated using seawater ratios of sulfate to
    sodium (our usual method, labeled NSS) and magnesium (may correct better 
    for soil particles blown up from the cliff, labeled NSSMg).
19-29) Error estimates for the ion concentrations They are 95% confidence 
    limits, based on blank variability, chromatogram baseline noise, and 
    chromatography uncertainty.  They do not include errors in the flow rate, 
    estimated at 10%, which affect all stages equally.