Similar to the AOS UHSAS and APS, the Scanning Mobility Particle Sizer (SMPS) and Nanoparticle SMPS (nano-SMPS) are AOS instruments that principally measure the number concentration of aerosol particles as a function of particle size - the so-called aerosol size distribution. The measurement concept is based upon the principle of electrical mobility - namely, that the ability of an aerosol particle to move through an electric field is fundamentally related to the size of the aerosol particle.
The nano-SMPS and SMPS specifically measure smaller-diameter aerosol particles - in the diameter range of:
As of now, please monitor the b1-level aossmps and aosnanosmps datastreams for all respective SMPS DQA assignments. When submitting DQPRs for either the SMPS or nano-SMPS, please use the SMPS instrument class under the AOS Group.
Both the SMPS and nano-SMPS are component instruments within the Aerosol Observing System (AOS). For a more complete overview the AOS system and its general backing measurement theory, please see the AOS DQ Wiki page.
In the metrics table below, the one primary SMPS measurement is outlined in red; the other measurement is diagnostic in nature. That primary field is:
In the metrics table below, the one primary nano-SMPS measurement is also total_concentration; all other measurements are diagnostic in nature. That primary field is:
The primary measurement made by the SMPS and nano-SMPS is that of aerosol particle size distribution - the number concentration of aerosol particles as a function of both particle diameter and time. Remember that the SMPS and nano-SMPS scan particle diameters through the smaller modes of aerosol sizes.
These 2D SMPS and nano-SMPS size distributions are plotted for both daily and weekly timescales. Before plotting, these number size distributions are put in dN / dlogDp form; for the motive behind this manipulation, see this resource. Particle diameters are on the logarithmic y-axis, and the z-axis (colorbar) shows the dN / dlogDp aerosol particle number concentration.
Note the different diameters scanned by each instrument; the nano-SMPS scans to smaller particle diameters than does the SMPS.
These aerosol number size distributions are totaled over all of the particle diameter bins scanned by each instrument to get a 1D total particle number concentration through time.
From the entire SMPS and nano-SMPS aerosol particle size distributions, we also plot a number of characteristic/statistical particle diameters on daily and weekly timescales. Namely, the mean, geometric mean, mode and median particle diameters of the entire size distributions. For a better understanding of how these characteristic diameters relate to one another, see this general resource.
In addition to the primary aerosol-related fields, a number of SMPS and nano-SMPS diagnostic fields are also plotted to better monitor the "health" of the instrument. These diagnostic fields include sample temperatures, pressures, relative humidities and the flow rate of air through the internal impactor.
Aerosol particle number concentrations are a common measurement amongst a number of AOS instrumentation. When available, these different collocated particle concentration measurements are plotted on top of one another in order to identify gross deviations in particle concentrations measured by single sensors within this group. While these measurements may be slightly different in magnitude from one another (due to physical instrument differences, calibrations, corrections, etc.), they should all generally trend well with one another.
Aside from the SMPS and nano-SMPS, a number of other AOS instruments also measure aerosol particle number size distributions over different particle diameter ranges. Some of these particle diameter ranges overlap with one another. In order to assess how these number size distributions compare across instruments, we create a comparison plot of the daily-mean aerosol particle number size distributions from each collocated AOS instrument. Generally, size distributions from different instruments should overlap one another over aerosol particle diameters that they both scan over.
Note that the usual temporal x-axis has been replaced with aerosol particle diameter (log scale); the daily mean dN / dlogDp number concentration is on the y-axis. The different particle diameters scanned by each instrument should be more apparent in the different instrument traces in this plot (i.e., from very small-diameter nanoparticles with the nano-SMPS to large-diameter coarse mode particles with the APS).
When available, we can compare the total, integrated aerosol number concentrations from the SMPS size distributions to aerosol number concentrations from collocated CPCF instruments. The two number concentrations should be highly comparable through time, such that deviations of these two measurements could be indicative of instrument problems.
In the top panel, we show the 1D total particle concentrations from both the SMPS and CPCF. In the bottom panel, we show the ratio of SMPS:CPCF number concentrations to aid in keying us in to differences between the two measurements. In general, this ratio should be ~1; if it starts to deviate from 1, there could be either a problem affecting the SMPS or CPCF.
This plot is produced on both daily and weekly timescales.
When available, we can compare the total particle number concentrations between the SMPS and the CPCF through a scatter plot like the one shown below. These scatter plots make it easier to see any disagreement between the measured SMPS and CPCF concentrations at certain times.
From the mentor:
These plots are available on daily and weekly scales.
When available, we can compare the volume concentrations between a number of AOS instruments in a plot like the one shown below. These plots make it easier to see any disagreement between the measured volume concentrations at various times, and are plotted on top of one another to be able to see any notable deviations in volume concentrations quickly and easily. It is important to keep in mind when viewing these plots that the values themselves may be slightly different in magnitude (due to differences in the instruments themselves, in calibrations, in coefficients, etc.), but they should still track well with each other - if one goes up or down, the others should follow suit. The nano-SMPS volume concentration, for example, should always be significantly lower than the rest of the volume concentrations, since it covers a smaller size range.
These plots are available on daily and weekly scales.
There are SMPS instrument systems at SGP E13 and as part of the AMF2 AOS system. A nano-SMPS is deployed at SGP E13.
Known behaviors that may not need to be mentioned in DQAs and DQPRs are listed below.
In some SMPS and nano-SMPS aerosol particle size distribution data, you may see a repeating signature associated with a physical phenomena called new particle formation. These events occur when a large number of small particles form through gas-to-particle conversion processes. Oftentimes, this gas is sulfuric acid. Gradually, these small particles grow in size, resulting in increased numbers of larger particles. In the weekly example below from the SMPS, there are a couple such new particle formation events (e.g., ~02/16, 02/17 and 02/18).
There is no need to make note of these events in your DQAs or submit DQPRs on them. Just appreciate their scientific importance.
Problems that do need to be mentioned in DQAs and potentially DQPRs are mentioned below.
A clogged impactor can lead to a change in the aerosol sample flow rate of the SMPS. This influences the reported number concentration and particle size distribution data. See DQPR 4154 or DQPR 8074 for details.
If you notice a sudden change in aerosol sample flow rate or sample pressure, it is worth mentioning in a DQPR, as well as in your DQAs.