The AOS Single Particle Soot Photometer (SP2) is an instrument designed to measure the concentration of black carbon (soot) within single aerosol particles. Atmospheric black carbon - which is formed through incomplete combustion of fossil fuels (e.g., diesel, coal), biofuel and biomass - absorbs solar energy, and thus, can influence climate through the the direct and indirect radiative effects.
The SP2 shines a high-power laser on the aerosol particles, and any black carbon within the particles absorbs that light, heating the particles to the point of incandescence. The emission of that incandescence is used to back out the particle's black carbon mass. Note that the SP2 also employs a scattering detector, which is primarily used to probe black carbon mixing state.
As of now, we at the DQO are tasked with monitoring an SP2 datastream that contains only "auxiliary" diagnostic fields from the instrument (i.e., the "heartbeat" of the instrument, rather than a science-ready end product). Please monitor the a0-level aossp2aux datastreams for all SP2 instrument systems. When submitting DQPRs for the SP2, please use the SP2 instrument class under the AOS Group.
For more information, please see the SP2 Instrument web page. You can also find more technical SP2 documentation at the vendor's website.
The SP2 is a component instrument 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 two primary measurements are outlined in red; all other measurements are diagnostic in nature. That primary fields are:
The DQ Office plots a number of SP2 diagnostic fields to monitor general instrument health on daily and weekly timescales. These include particle concentrations from the scattering and incandescence channels; the flow rate of sample air through the instrument; laser power; and diagnostic temperatures and pressures.
The SP2aux datastream contains a diagnostic particle concentration as measured by the incandescence channel. At the DQO, we plot this SP2aux incandescence concentration alongside particle concentrations from a collocated CPC(F) for comparison purposes.
Note that while the magnitude of these two particle concentrations may not be congruent, they should generally trend well with one another in time. That is, SP2aux incandescence counts should be high when CPC(F) particle concentrations are high, and vice versa.
No known behaviors that may not need to be mentioned in DQAs exist. Document some here.
Past problems that do need to be mentioned in DQAs and potentially DQPRs are mentioned below.
Periodically, the measured rate of sample air through the SP2 can deviate from its "set point" (the desired flow rate through the instrument). Significant sample flow rate deviations will be highlighted in both the QC metrics tables and in the diagnostic plots. They could be related to such problems as instrument clogs, amongst others.
Action: If you see this behavior, please issue a DQPR.