Operations Updates
ARM Climate Research Facility Operations Update - September 15, 2006
This bimonthly report provides a brief summary of significant accomplishments and activities in the operations area of the ARM Climate Research Facility (ACRF).
Trace Gases Targeted During Aircraft Carbon Field Campaign
During the Aircraft Carbon field campaign, ARM researchers will add a set of carbon-cycle instruments and sample collection systems to existing aircraft that routinely collect aerosol measurements at the ACRF Southern Great Plains site.
Because Earth's atmosphere is comprised almost entirely of nitrogen and oxygen (78% and 21% by volume, respectively), the remaining 1% of the gases are referred to as "trace gases." Trace gases include harmless inert gases, such as helium and neon, but also radiatively active gases, like methane and carbon dioxide. These latter gases, especially carbon dioxide, have been shown to enhance Earth's natural greenhouse effect. As such, their contribution to global climate change is the focus of much research. July 2006 marked the beginning of a two-and-a-half year field campaign at the ACRF Southern Great Plains (SGP) site to obtain airborne trace-gas measurements.
During the first year of the Aircraft Carbon field campaign, ARM researchers will focus on developing the capability to measure continuous carbon dioxide concentration profiles from the surface to mid-troposphere (i.e., 5-7 km). Such measurements will facilitate calibration of the Orbiting Carbon Observatory and improve computer models that simulate Earth's carbon budget. They will also augment existing flask-based collection of trace gases (carbon monixide, methane, and stable isotopes of carbon dioxide, or 13CO2) by sampling at more heights and adding a sampler for radiocarbon (14CO2). This suite of trace gases, enhanced by the continuous carbon dioxide profiles, will provide comprehensive data for inverse methods that infer ecosystem carbon exchange and quantify anthropogenic (manmade) combustion emissions.
After the first year, researchers plan to add three other temporary measurement systems: (1) a collection system for large air volumes (mainly to capture 222Radon, a tracer for atmospheric transport), and (2) equipment for trapping of water vapor for isotopic analysis.
Additional collaborators will support developing the instrument systems, analyzing the data, and ingesting all data to the ARM Data Archive. Trace gas measurement obtained at the SGP during this campaign will provide valuable data for addressing carbon-cycle questions stressed by the U.S. Climate Change Science Program and the North American Carbon Program.
New Instrument "Counts" Cloud Particles
The CCN Counter consists of a vertical column with wetted walls, which provides the water vapor necessary to produce super-saturations. Particles activate into droplets when exposed to the super-saturated conditions, and the droplets are then counted by an optical particle counter.
Microscopic airborne particles are commonly referred to as "aerosols." Every one of the trillions of droplets in a cloud originates on one of these tiny "cloud condensation nuclei" (CCN). Through their role as CCN, aerosols affect cloud properties by altering the concentration of cloud droplets, and the brightness (reflectivity) and lifetime of clouds. These "indirect aerosol effects" are difficult to quantify, yet are essential to improved understanding of how clouds affect Earth's incoming and outgoing energy. The ability to model aerosol indirect forcing is a priority for the ARM Program.
To characterize how changes in CCN concentrations may be changing the properties of clouds observed at ACRF's Southern Great Plains (SGP) site, in September a CCN Counter was added to the suite of instruments that comprise the site's Aerosol Observing System (AOS). Built by Droplet Measurement Technologies, the instrument measures CCN number concentration at supersaturations between 0.1 - 2%. An optical particle counter measures the size distribution of the droplets that grow from CCN, collecting data every second in 20 particle size bins from 0.75 to 10 microns. Data sets from the CCN Counter at SGP will be available from the ARM Data Archive on a quarterly basis, following data quality review by the AOS instrument mentor team.
Ultimately, the goal is for AOS systems at each ACRF site to use identical components, including the CCN Counter. As part of the AOS for the ARM Mobile Facility (AMF), an identical CCN instrument was deployed in 2005 during the AMF field campaign at Point Reyes, California, and is currently operating at Niamey, Niger, West Africa.
