Experimental Science Section (ESS)

Observational data are the foundation upon which our knowledge of atmospheric composition, trends and processes are based. These data also provide the drivers for continued improvement and development of Earth system models. ACOM has a long heritage of making high quality measurements of atmospheric composition, in collaboration with members of the wider atmospheric chemistry community. Measurements are made in the laboratory as well as in-situ from aircraft or at ground sites, or via remote sensing techniques involving satellite- and ground-based instrumentation.

In-situ observations have long been a centerpiece of ACOM activities. This research is conducted in partnership with NSF NCAR EOL, and in collaboration with and in support of the activities of the wider atmospheric chemistry research community. Current commonly deployed in-situ ACOM measurements available to the community include VOCs (TOGA-TOF), NO/NO_x/O₃ (AON), Actinic Flux (HARP/CAFS), CO, CO₂, CH₄, N₂O, O₃ and H₂O (Core Atmospheric Tracers). 

Two other instruments are under development: the APROC (ACOM Project for the Revitalization of Observational Capabilities) Aircraft WingPod CIMS instrument, a capability that ACOM does not currently have in its suite of instruments that will measure advanced VOC oxidation products that are critical to our understanding of atmospheric processes leading to aerosol and ozone formation; and a laser induced fluorescence (LIF) instrument for the measurement of NO/NO_x that will provide more precise measurements and lower detection limits for species that are absolutely critical for any field measurement campaign. 

Another key ACOM activity is centered around simulating the atmosphere under tightly controlled conditions in environmental chambers. Two chambers are currently in use: A 50-L, temperature controlled stainless-steel environmental chamber interfaced to an FTIR spectrometer and a GC-FID system for mechanistic studies and relative rate coefficient determination, and a 10-m³ Teflon walled chamber for atmospheric organic mechanism studies. This chamber is equipped with control instrumentation (flow rates, ozone, temperature, particle size distribution, relative humidity, pressure, and light control), and gas chromatography (GC), proton-transfer reaction – mass spectrometry (PTR-MS), and chemical ionization mass spectrometers (CIMS) for the chemical characterization of chamber contents. Additional ACOM and community instruments can be added for targeted experiments.

Research foci for the section include characterization of biogenic, fire, and anthropogenic emission sources and reaction pathways and their impact on air quality and climate, impact of halogenated species (with an emphasis on VSLS) on lower stratosphere ozone distributions, oxidation mechanisms via OH/Cl/NO₃ site-of-attack on VOC compounds, and reaction mechanism characterization and development of structure-reactivity relationships. These relationships derived both by ACOM and collaborating scientists are used to drive fully explicit chemical mechanism generators GECKO-A and Mech-Gen which are under development in the section.

For questions about ESS, please contact Eric Apel, ESS Section Head.