The NOAA Earth System Research Laboratory (ESRL) Federated Aerosol Network consists of surface aerosol monitoring stations around the world owned and operated by either ESRL or by Collaborating Institutes (CI's). At the present time, six stations are wholly funded and maintained by the ESRL Global Monitoring Division (GMD) Aerosol Group, and there are approximately twenty many more stations whose operations are primarily funded by the CI's. NOAA provides central services for the network, including development and maintenance of free software for data acquisition, processing, analysis, and submission to public archives, as well as automated data processing, generation of quick-look data plots (e.g., for Bondville), and generation of summary statistical plots (e.g., for Bondville). Comparability of measurements across the network depends not only on similar instruments, data processing, and quality control data inspection, but also on similar sampling protocols and measurement methods, including schedules for system inspections, calibrations, routine maintenance, and repairs. Below we briefly discuss the methods and schedules used at the NOAA/ESRL stations so that our partners at the CI's are aware of these requirements for measurement comparability and smooth aerosol system operation.
A typical NOAA-type aerosol measurement system consists of an aerosol sampling stack, one or more instruments to measure aerosol optical and/or microphysical properties, and the required supporting hardware, electronic, and computer/data-logging components. While some sites have a large suite of aerosol instrumentation, most have, at a minimum, multi-wavelength light scattering and light absorption measurements, and also total number concentration.
In addition to daily to weekly inspections where system operation is observed and obvious problems are addressed, the aerosol monitoring systems at NOAA-operated stations typically undergo a major, comprehensive inspection once each year. This annual inspection is for updating instrument calibrations if necessary, cleaning internal system components, and for identifying issues that might be overlooked during routine daily or weekly system checks. It is also for evaluating how system components are holding up, and to fix problems before they occur. This list shows a typical set of tasks for an annual maintenance visit to a NOAA station with a 'basic' aerosol system containing a NOAA-style aerosol inlet and rack system, and the light scattering, light absorption and particle number concentration instruments. As discussed above, some collaborators may have considerably more to do than this list implies because of additional instruments or system components, and some with smaller systems may not need to perform all of the items on the task list.
Many of the tasks on the list involve inspection, cleaning, and replacement if necessary, of components of the aerosol inlet and vacuum systems. The inlet system includes everything from the rain hat at the top of the sampling stack to the respective inlets of each aerosol instrument. These tubes and lines should be inspected for damage, corrosion, leaks, loose fittings, blockages, cleanliness, liquid water, and other problems. If any of these problems are found, corrective action is necessary. At a minimum, unless you are operating at a very clean site, the inlet system should be cleaned annually. The vacuum/flow system should also be inspected and maintenance items (see this newsletter's maintenance tip) addressed, with specific emphasis on the pump box and components therein. The support tower, guy wires, and anchors must be inspected annually for rust or corrosion that affect structural integrity. Calibrations of all flow, temperature, relative humidity, and delta-pressure sensors should be checked and recalibrations should be performed if necessary. Consumables such as filters, drier elements, etc., should be replaced at this time and the supply of spares replenished.
In addition to the NOAA stations, we travel to a few collaborating stations in the continental US to perform the described annual maintenance procedures. We can do this because travel costs are not high to these nearby stations and lodging may be provided by the collaborators. Even though we cannot routinely visit the international stations, we want to offer as much help as we can to our network partners, recognizing the considerable amount of work it takes to make high quality, long-term aerosol measurements. A properly running station in our network is of value to all parties and we will do everything we can to assist in this respect. We typically are available during normal daytime hours in Colorado for telephone conversations for science discussions, system troubleshooting, and maintenance/repair advice. Email questions and requests are answered as soon as possible and often outside of our normal working hours. We do have a limited stock of spare and consumable parts, which we can provide (contact us to let us know what you need and we will respond saying whether it is possible to accommodate your request). In general, we prioritize helping with smaller, less expensive items that may be costly to obtain overseas, or that have very long delivery times for international orders. We have also developed procedures for overhauling the motors in the TSI integrating nephelometers that most stations operate, and can provide overhauled motors in trade for failed motors.
We have formal arrangements with some of the international CI stations to visit once per year for an annual system check. Most stations, however, have no such agreement with NOAA. These are the stations that we want to make sure get a comprehensive annual checkup, and properly performing the items on the annual maintenance task list will accomplish this.
There are times when a collaborator may desire or require a visit by NOAA scientists. Long-term monitoring stations will lose experienced personnel over time and the new people will have to be trained. Occasionally station personnel retire, resign or have an extended absence and the remaining station operator(s) are left to handle everything and are overwhelmed. Sometimes multiple failures will occur in the aerosol system so diagnosing and fixing the problems can be quite difficult and time consuming. In these instances a station visit from NOAA scientists could be quite beneficial. NOAA scientists also work closely with the World Calibration Centre for Aerosol Physics (pdf download) of the WMO (World Meteorological Organization) in the framework of the Global Atmosphere Watch program (GAW), so we may be able to better prepare our collaborators for a GAW aerosol audit.
If at some point you decide that a NOAA aerosol scientist visit is necessary for the long-term health of your aerosol measurements, please contact us and we can discuss several possible options. If, for example, a NOAA scientist is 'in the area' for another reason, we could possibly schedule a visit during this time. For instance, NOAA scientists attended the 2012 European Aerosol Conference in Granada, Spain, but prior to the meeting traveled to the El Arenosillo station near Huelva, Spain for a system inspection and maintenance visit.
Feel free to contact us any time with questions or concerns about the operation of your aerosol system, and please don't be shy in asking for assistance if you need it!