Atmospheric Radiation Investigations and Measurements (ARIM)
Richard Shetter (Group Leader)
Photochemical reactions provide the driving force for much of the chemistry in the atmosphere, affecting the recovery of stratospheric ozone, the magnitude of the greenhouse effect, tropospheric air quality and evolution, and changes in surface ultraviolet (UV) radiation. Thus, in situ solar radiation measurements are critical to atmospheric composition research. The ARIM group measures spectrally resolved UV and visible actinic flux and derives photolysis frequencies for a variety of important chemical species, including O3, NO2, CH2O, HONO, HNO3, N2O5, HO2NO2, PAN, H2O2, CH3OOH, CH3ONO2, CH3CH2ONO2, CH3COCH3 , CH3CHO, CH3CH2CHO, CHOCHO, CH3COCHO, CH3CH2CH2CHO, and CH3COCH2CH3. Additionally, the actinic flux measurements, in conjunction with radiative transfer calculations, are used derive ozone column abundances. These ozone columns have proven to be very useful for satellite validation activities.
The group maintains Charged-coupled device Actinic Flux Spectroradiometers (CAFS) and Scanning Actinic Flux Spectroradiometers (SAFS) to measure up and down-welling wavelength dependent actinic flux in the UV and visible wavelengths. The measurements are based on a 2π steradian hemispherical zenith and nadir optical collectors coupled with UV enhanced fiber optic bundles to small, lightweight, monolithic CCD monochromators and double monochromator with photomultiplier tube detection, respectively. The instruments have an excellent record of performance on the NCAR HIAPER GV and C-130, the NASA DC-8, WB-57 and P-3B, the NOAA WP-3D and at numerous ground stations.
The ARIM optical calibration facility is equipped with precision radiometric power supplies and multiple NIST traceable 1000W quartz tungsten halogen lamps to determine the spectral response of each instrument. Secondary lamp standards are applied in the field. Mercury line calibrations are also performed to track the wavelength accuracy.
The ARIM work supports the ACD goals of understanding the regional and global air quality and the role of chemistry in the climate system.
Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS)
The 2008 ARCTAS (funded by NASA) mission investigated the transport and transformation of gases and aerosols affecting the Arctic. The winter phase was based in Fairbanks, AK, and explored the transport of pollution across the Arctic, with a focus on arctic haze, tropospheric ozone and surface deposited black carbon. The summer phase was based in Cold Lake, Alberta, and concentrated on the contribution of boreal fires to the atmospheric composition and climate of the Arctic region.
CAFS instruments were deployed on the NASA DC-8 aircraft for the full campaign to provide photolysis frequencies for the critical chemical constituents of the arctic. In particular, the photolysis contributes to the study of the evolution of pollution plumes and the tropospheric oxidant chemistry. Several factors specific to the arctic affected the actinic flux. The scattering in arctic haze tends to increase the flux while absorption in boreal fire emissions decreases the flux. Surface deposited black carbon also decreases the flux by reducing the surface albedo. Thus, the in situ measurements were critical to assessing the local radiation field.
Prior to the summer phase in Cold Lake, Alberta, the California Air Resources Board funded a series of flights based from the NASA Palmdale facility to study the dynamics of the transport of Asian pollution into California, local anthropogenic pollution and greenhouse gas emissions. Again, the actinic flux measurements were critical to understand the local chemistry and evolution of the emissions. The extensive California wildfires were also studied. The actinic flux was often dramatically reduced within the fire plumes, slowing the photolysis chemistry.
The CAFS instruments were redesigned for DC-8 installation, including new instrument housings, PC-104 computers and electronics, and upgrades to the data acquisition and control software. Data coverage was near 100% for the entire mission.
HIAPER Aircraft Instrumentation Solicitation Experimental Flight Test – 2008 (HEFT-08)
The ARIM team, in collaboration with Peter Pilewskie and Bruce Kindel of the University of Colorado, Manfred Wendisch of the Leibniz-Institute for Tropospheric Research, Rainer Schmitt of Metcon, Inc and Dieter Schell of Enviscope GmbH, Germany, developed the HIAPER Airborne Radiation Package (HARP), a comprehensive atmospheric radiation suite to measure in situ actinic flux and irradiance. The package is part of the HIAPER Aircraft Instrumentation Solicitation (HAIS), funded by NSF. The ARIM group developed the actinic flux package using a CAFS detection and was responsible for building the spectrometer computer systems, creating the data acquisition and control software, coordinating the assembly of the racks, equipment, input optics and stabilized platforms, and leading the integration and flight management of the instrumentation.
The irradiance measurements rely on horizontal stabilization to determine layer properties, such as reflectance, transmittance and absorbance. Thus, the HARP irradiance package is mounted on zenith and nadir stabilized platforms to account for aircraft attitude changes. The platform was tested during HEFT-08. The stabilized platform performed well and responded precisely to positional commands. However, the navigation signals used to determine aircraft attitude were inaccurate due to signal timing delays and noise on the signal line. To eliminate these external errors, the HARP system has been upgraded to receive direct GPS antenna signals. Final testing and delivery of the HARP instrumentation is forthcoming.
The recent ARIM group publications cover a broad range, including chemical measurement and model studies, satellite validation of ozone columns, and atmospheric heating rates.
Measurement of HO2NO2 in the Free Troposphere during INTEX-NA 2004, S. Kim, L.G. Huey, R.E. Stickel, D.J. Tanner, J. H. Crawford, J.R. Olson, G. Chen, W. H. Brune, X. Ren, R. Lesher, P. J. Wooldridge, T. H. Bertram, A. Perring, R.C. Cohen, B., B. Lefer, R. E. Shetter, M. Avery, G. Diskin, and I. Sokolik, J. Geophys. Res., 112, D12S01, doi: 10.1029/2006JD007676.
Improving regional ozone modeling through systematic evaluation of errors using the aircraft observations during the International Consortium for Atmospheric Research on Transport and Transformation, Mena-Carrasco, M., Y. Tang, G. R. Carmichael, T. Chai, N. Thongbongchoo, J. E. Campbell, S. Kulkarni, L. Horowitz, J. Vukovich, M. Avery, W. Brune, J. E. Dibb, L. Emmons, F. Flocke, G. W. Sachse, D. Tan, R. Shetter, R. W. Talbot, D. G. Streets, G. Frost, D. Blake, 2007:. J. Geophys. Res., 112, D12S19, doi: 10.1029/2006JD007762.
HOx chemistry during INTEX-A 2004: Observation, model calculations and comparison with previous studies, Ren, X., J. R. Olson, J. H. Crawford, W. H. Brune, J. Mao, R. B. Long, Z. Chen, G. Chen, M. A. Avery, G. W. Sachse, J. D. Barrick, G. S. Diskin, L. G. Huey, A. Fried, R. C. Cohen, B. Heikes, P. Wennberg, H. B. Singh, D. R. Blake, R. E. Shetter, , Journal of Geophysical Research, 113, D05310, doi:10.1029/2007JD009166, 2007.
Algorithm for the charge-coupled-device scanning actinic flux spectroradiometer ozone retrieval in support of the Aura satellite validation, Petropavlovskikh, I., R. Shetter, S. Hall, K. Ullmann, P. K. Bhartia, , J. of Appl. Remote Sens. 1, 013540 (2007), doi:10.11171.2802563.
OMI total ozone column validation with Aura-AVE CAFS observations, Kroon, M., I. Petropavlovskikh, R. Shetter, S. Hall, K. Ullmann, J. P. Veefkind, R. D. McPeters, E. V. Browell, and P. F. Levelt (2008), , J.Geophys. Res., 113, D15S13, doi:10.1029/2007JD008795.
In-flight validation of Aura MLS ozone with CAFS partial ozone columns, Petropavlovskikh, I., L. Froidevaux, R. Shetter, S. Hall, K. Ullmann, P. K. Bhartia, M. Kroon, and P. Levelt (2008), , J. Geophys. Res., 113, D16S41,doi:10.1029/2007JD008690.
Calculations of solar shortwave heating rates due to black carbon and ozone absorption using in situ measurements, Gao, R. S., S. R. Hall, W. H. Swartz, J. P. Schwarz, J. R. Spackman, L. A. Watts, D. W. Fahey, K. C. Aikin, R. E. Shetter, and T. P. Bui (2008), , J. Geophys. Res., 113, D14203, doi:10.1029/2007JD009358.
Role of convection in redistributing formaldehyde to the upper troposphere over North America and the North Atlantic during the summer 2004 INTEX campaign, Fried, A., et. al.(2008), J. Geophys. Res., doi:10.1029/2007JD009760.
FY 2009 PLANS
The ARIM group will continue data analysis on previous missions and publication of the results from the MIRAGE, TC4, CR-AVE and ARCTAS missions. In addition, we will begin comprehensive improvements to the CAFS measurements. These include quantification of stray light in the instruments, wavelength assignment corrections, and a calibration source intercomparison. We plan to investigate extending the CAFS wavelength range and optimizing the integration time and internal averaging with signal to noise. Instrument modifications will focus on improving the temperature and relative humidity control and monitoring, to provide a safe and optimal measurement environment. We will also continue collaborating with Irina Petropavlovskikh at NOAA/SRRB to improve the ozone column calculations.
OASIS (Ocean-Atmosphere-Sea Ice-Snowpack)
The February-April 2008, OASIS project (funded by NSF) in Barrow, Alaska will investigate fluxes between the atmosphere and snowpack, ozone depletion events, halogen chemistry and arctic haze. These are all driven by the photochemistry, so the ARIM surface actinic flux will be a critical measurement. The photochemistry will ramp up dramatically during the two month deployment, as the day will expand from 6 to 17 sun hours and the maximum solar zenith elevation increases from approximately 7 degrees to 29 degrees.