¶ Aerosol Observing System Ozone Monitor (AOSOZONE/AOSO3)
¶ Instrument Description
An in-situ Ozone Monitor measures the concentration of atmospheric ozone, an important gaseous constituent of the lower troposphere and a greenhouse gas. The technique used to measure ozone concentrations is based upon the absorption of ultraviolet light, the same principle that occurs naturally in the stratosphere, where the ozone layer absorbs and effectively blocks most ultraviolet light from reaching earth's surface.
As of now, please monitor the b0-level aoso3 datastream for all ozone DQA assignments. A b1 level of this datastream exists, but there will be a lag with this data, while b0 level data should remain up to date. When submitting DQPRs for the ozone instrument system, please use the OZONE instrument class under the AOS Group.
¶ Additional Information
For some additional, please see the OZONE Instrument web page. You can see an example overview of an ozone monitor at this vendor's website.
As the tropospheric ozone Wikipedia page puts it (see great description of tropospheric ozone formation therein), "The majority of tropospheric ozone formation occurs when nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOCs), react in the atmosphere in the presence of sunlight." The latter, sunlight-dependent chemical reaction is known as photolysis. Knowing this, a question for further thought: what do we expect the diurnal cycle of ozone concentrations to look like at different locations around the globe?
For a brief and general primer on ozone measurement theory, check out the video below:
The ozone monitor 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.
¶ Expected Operations
¶ Metrics
In the ozone monitor metrics table below, o3 is the primary measurement; all other measurements are diagnostic in nature.
¶ Plots
¶ Ozone concentrations and diagnostic fields
The daily and weekly plot sets for the ozone monitor are shown below - there's only one primary variable plot (o3 concentration in ppb), and a few diagnostic plots. The "aos_ozone_cal" plot shows the average ozone concentrations at the different gas states. The diagnostic plots are primarily measurements of housekeeping variables to be sure the instrument is working properly. They include ozone pressure, the ozone lamp and bench temperatures, the flow rates through cells A and B, and the lamp level percentage.
NOTE: Each of these panels also have corresponding weekly plots.
¶ Site Specific Information
The OZONE is currently located at ENA C1, SGP E13, AMF1 as part of the Mobile Aerosol Observing System (MAOS), AMF2, and AMF3. Instruments at all locations operate similarly.
¶ Known Issues
¶ Known Behaviors
The following issues may not need to be mentioned in DQAs.
¶ Operational not available gaps
Every day at ~00:00 and ~12:00 UTC, all ozone monitors go through a series of operational calibration maneuvers. These maneuvers last for ~10 minutes, and manifest themselves in our QC metrics as a short period of "Not Available" data or "Bad" data (see example below). Ozone concentrations during these calibration periods are often noisy and not representative of the atmosphere. See the periods of noise marked with black arrows below.
You can simply ignore these calibration maneuvers when monitoring the ozone instrument systems. There's no need to make note of this behavior in your DQAs.
¶ Past Problems
Problems that do need to be mentioned in DQAs and possibly DQPRs are listed below.
¶ Non-operational pump
From time to time, the internal pump on the ozone monitor stops working or breaks altogether. Often, this manifests as flatlined measured ozone concentrations and perhaps slightly higher internal instrument pressures.
Action: If you see this behavior, please issue a DQPR.
¶ Dirty filter
As part of the operational procedures in place to maintain the ozone monitors, site operators are supposed to change out the instrument filter every other week.
Action: If you see similar persistent noise in the ozone concentration fields (lasting more than a couple days), consider issuing a DQPR.
¶ Large Oscillations in the Signal
Sometimes, the AOSO3 instrument can suffer major oscillations in the signal. In the case below, it was discovered that the Split System Air Conditioner was blowing directly on the Ozone detector, causing water to condense in the line. The air was redirected and the temperature setpoint raised. This reduced but didn't entirely eliminate the oscillations.
Action: If you see similar persistent oscillations in the ozone concentration fields (lasting more than a couple days), consider issuing a DQPR.