Community Airborne Research Instrumentation (CARI) Group

CARI Group members:

• Eric Apel
• Teresa Campos
• Frank Flocke (head)
• Clifford Heizer (joint with RAF)
• Alan Hills
• David Knapp
• Denise Montzka
• Ilana Pollack
• Andrew Weinheimer
• Wengang Zheng

Overview

The recently formed CARI group is currently responsible for a number of aircraft trace gas instruments, including instrumentation which can be requested via the NSF/LAOF process, NSF/NCAR GV (HIAPER) instruments (two of those are part of the HAIS suite), and others. These instruments are:

• CO: Two vacuum flourescence instruments (Aerolaser, one certified for GV)
• CO2: Broadband infrared absorption carbon dioxide instruments (modified Li-Cor)
• H2O: Two TDL infrared absorption open-path water vapor instruments (MayComm Instruments, one certified for GV)
• Fast-O3: "Inverse" NO chemiluminescence instrument (home built for GV - HAIS)
• NO, NOy: compact 2-channel chemiluminescence instrument / photolytic conversion /gold catalytic conversion (home built for GV)
• NOx, NOy, O3: 4- channel chemiluminescence instrument / photolytic conversion /gold catalytic conversion (NO, NOy (g), NOy (total), O3, home built for various aircraft, not certified for GV)
• PANs: Thermal dissociation Chemical Ionization Mass Spectrometer (built in collaboration with Georgia Tech)
• VOC: TOGA fast GC-MS instrument measuring a variety of VOC (alkanes, alkenes, oxygenates, aromatics, and others, about 40 compounds total) on a 2-min time scale (home built for GV - HAIS)

The group expects to take responsibility for one or more additional HAIS instruments after they have been delivered to EOL.

Summary of Activities for FY07:

Field Experiments and instrument preparation/improvements:

CARI participated in five field experiments in the last year. The TexAQS 2006 campaign, led by NOAA ESRL and funded by NOAA ( http://www.esrl.noaa.gov/csd/2006/ ), the Pacific Dust Experiment (PACDEX; funded by NSF), the Airborne Carbon in the Mountains Experiment (ACME; funded by NSF), The Pacific Sulfur Experiment (PASE; funded by NSF), and the Tropical Composition, Cloud and Climate Coupling (TC4) experiment (led and funded by NASA).

The TexAQS 2006 experiment was flown on board the NOAA P-3 in September and October 2006. CARI participated with the PANs- CIGARette instrument. This effort is described separately under the "Megacities and the Effects of Urbanization" section. Final data was delivered to the data archive and data analysis and interpretation has begun. First results were presented at the TexAQS 2006 data workshop in Austin, TX, in August.

The Pacific Dust Experiment (PACDEX), April and May, 2007, tracked Asian plumes as they advected across the Pacific, characterizing the extent of transpacific transport of continental components including dust, black carbon and CO. A particular focus of PACDEX was characterization of cloud interactions with these plumes and airmass physical and composition changes resulting therefrom. Chemical, meteorological forecasts, as well as dust and CO satellite products enabled the investigators to predictably locate and sample the plumes in a quasi-Lagrangian manner. The CARI CO instrument was deployed on the NSF/NCAR G-V as a combustion tracer.

The Airborne Carbon in the Mountains Experiment (ACME-07), April 4 - August 10, 2007, undertook a Lagrangian approach to quantify regional integrated carbon fluxes over the heterogeneous terrain of the Colorado Rocky Mountains. The 2007 airborne component of the Carbon in the Mountain Experiment (CME) helped constrain model flux estimates and extend inferences drawn from the CME network of continuously monitoring ground sites. The CARI group provided mission-critical measurements of CO and CO2 mixing ratios on the UW King Air platform. Improvements to the airborne CO2 instrument electronics and data acquisition system were implemented in preparation for the ACME-07 campaign. Improved noise specifications and reliability of operation were observed.

CARI configured the 2-channel NO-NOy instrument for flight in a pallet on the WB-57F for participation in TC4. This proved to be a valuable testing opportunity and has led to design changes that will be incorporated before the instrument is flown again.

The Pacific Atmospheric Sulfur Experiment (PASE), August 1 - September 8, 2007, studied the chemistry and dynamics of sulfur species in the clean marine boundary layer, with a special emphasis on the impact of these species and their oxidation products on local aerosol physics, including CCN. The CARI group provided CO, fast-Ozone and water vapor mixing ratio measurements on the NSF/NCAR C-130. The fast-response ozone and water vapor measurements additionally will support estimations of boundary layer entrainment rates.

Data Analysis and interpretation

MIRAGE
TOGA volatile organics measurements were combined with whole air sample analyses from the University of California, Irvine to obtain an understanding of the distribution of non-methane hydrocarbons (NMHCs), oxygenated volatile organic compounds (OVOCs), halogenated compounds and acetonitrile, an important tracer for biomass burning in the MCMA and areas of Mexico away from the city. Above the MCMA, the most abundant VOC measured was methanol followed by propane, formaldehyde, acetone, and acetaldehyde. The most reactive VOCs in terms of OH-reactivity were acetaldehyde, formaldehyde, propanal and methanol (see Figure 1). We speculate that short-lived (highly reactive) low molecular weight VOC species provide the primary driving force for ozone formation in Mexico City and that in the MCMA the lifetimes are short enough so that there is little carry over from day to day. Primary emissions of ethylene, propylene, formaldehyde, and acetaldehyde (and secondary formaldehyde and acetaldehyde production from the oxidation of ethylene and propylene) are the important low molecular weight OVOCs. This work suggests that there is potential for significant reductions in oxidant formation from efforts to reduce the emissions of these few species.

Figure 1: Distribution of VOC and reactivity in Mexico City.

The reactive nitrogen measurements made on the C-130 were combined to investigate the budget and speciation of NOy in the Mexico City (MC) plume. Figure 2 shows the evolution of NOy partitioning in the outflow from Mexico City compared to New York City (NYC, from ICARTT 2004). It is apparent that in the relatively low-altitude, high humidity and temperature environment downwind of NYC the PAN reservoir is relatively small and almost all of the emitted NOx is converted to HNO3 within one day. Ozone production further downwind will therefore be limited by the availability of NOx. The MC outflow, on the other hand, occurs at higher altitudes (because of the elevation of the city combined with a very high PBL up to 5 km asl) and therefore lower temperatures. PANs comprise about half of the NOy after 2 days of transport and through slow decomposition maintain a NOx level which is sufficient to continue to produce ozone for several days downwind of the city.

Figure 2: NOy partitioning and ozone production downwind of Mexico City (top) New York City (bottom, from ICART 2004).

As part of further study of the evolution of NOy partitioning, the sampling of the aerosol component of NOy needs to be better understood. The flow around the NOy inlet is being modeled (Fluent software), along with the aspiration efficiency of NOy-containing aerosols for a quantitative evaluation of the aerosol component of the NOy measurement. This work will involve a collaboration with investigators (Jimenez et al., U of Colorado) who operated the Aerosol Mass Spectrometer (AMS) on the C130 during MIRAGE. As a first step in this analysis, the flow field around the NOy inlet has been modeled (Figure 3).

Figure 3: Velocity vectors for 200 m/s aircraft speed over inlet showing recirculation.

INTEX-B
TOGA VOC measurements made on board the C-130 during INTEX show strong evidence of oceanic uptake of several oxygenated VOC. Figure 4 shows a composite of all altitude profiles of acetone, methanol and CO flown over the ocean. Acetone and methanol show clear decreases in the surface layers while CO does not. The MOZART model does not capture this observed decease because ocean uptake is not included in the model (methanol is underestimated because the sources of methanol are not well known at this time and strongly underestimated in global models), while the profile of CO is well reproduced. Oceanic uptake rates of 4.7 and 3.3 µmole m2 day-1 can be derived for acetone and methanol, respectively. The previously reported oceanic uptake rate for acetonitrile (deGouw et al.) was included in the MOZART model and the altitude profiles observed by the TOGA instrument were well reproduced with the model.

Figure 4: altitude profiles of VOC and CO mixing ratios over the Pacific measured during INTEX-B with the TOGA instrument.

OVOC Intercomparison
The first large scale in-situ intercomparison of oxygenated volatile organic compound (OVOC) measurements was conducted blind at the large (270 m3) simulation chamber, SAPHIR, in Jülich, Germany. Fifteen analytical instruments from Europe, representing a wide range of techniques, from GC-FID to DOAS to TOF-PTR-MS and more, were challenged with measuring atmospherically relevant OVOC species and toluene (15 species, C1 to C7) in the approximate range of 10-0.6 ppbv (simulated moderately polluted conditions). The SAPHIR chamber proved to be an excellent facility for conducting this experiment. Measurements from individual instruments were compared to mixing ratios calculated from the chamber volume and the known amount of OVOC injected into the chamber. A PTR-MS instrument showed the best overall performance in this study but a number of other techniques also performed well. All techniques demonstrated the potential for measuring OVOCs quantitatively but this study showed that improvements are necessary for the majority of them, especially if they are to be deployed for ambient measurements. Benzaldehyde and 1-butanol, compounds with the lowest vapor pressure of those studied, presented the most overall difficulty because of a less than quantitative transfer through some of the participant's analytical systems.

Megacity Study
CARI is also involved in a study of critical aspects of the carbon, nitrogen and oxygen cycles within a number of large urban area in different development stages: Tokyo, Japan; Dubai, United Arab Emirates; Lagos, Nigeria; Mumbai, India; and Buenos Aires, Argentina. A suite of measurements are being taken of speciated gas and aerosol phase carbon, nitrogen containing compounds, and ozone, during multiple years (2007-2009). Data analysis will be coupled with models to discern the linkages among megacities and the local, regional, and global environment. From these studies we hope to create an awareness of the impacts of developed and developing megacities on the environment and to emphasize opportunities for the mitigation of adverse effects. CARI is providing measurements of VOC and CO measurements for this study.

Other
Data is being prepared, QA'd and archived for all other field missions in which CARI participated. CARI has submitted six presentations at the AGU Fall Meeting presenting results from MIRAGE, INTEX-B, TexAQS2006, PACDEX, and instrument development.

Plans for FY08:

Instrumentation Research and Development:

For information about current instrument development done by the CARI group please also refer to the ESSL laboratory annual report sections on "Community Chemistry Instruments", "Atmospheric Chemistry Instrumentation" and "HIAPER instruments". Please also refer to the following paragraph which describes the specific tasks related to preparing our instruments for participation in the FY2008 field programs that requested CARI instruments.

Both HAIS instruments, the Fast-O3 and the TOGA VOC analyzer are slated for completion during FY2008. The NO-NOy and the Fast-O3 instruments will be reconfigured and flown on HEFT and START-08. The first deployment for the HAIS-TOGA instrument will likely take place in FY2009.

We are planning to integrate instrument control and data acquisition functions of the Fast-O3, NO-NOy and CO instruments. Furthermore, we are planning to share some components (such as pumps, pressure control and gases) between all three or pairs of these instruments in order to save weight and rack space on the GV if they are requested together as part of a chemistry or tracer package, which we expect to happen frequently (see START-08).

We are also planning to improve instrument control and electronics in our CO2 instruments and enable raw data acquisition which we expect to significantly improve the data quality and lower the detection limit.

Modifications to the PAN-CIGARette CIMS instrument will begin in FY2008 which are directed to certification for use on the GV. The CIGARette is already much more compact than the first generation PAN-CIMS instrument and only requires one side of a standard double rack or one GV rack space and weighs just over 200 lbs.

Field campaigns:

In FY2008, CARI will participate in five field deployments. The international water vapor intercomparison (AquaVit) in October in Germany (funded by the German BMBF and the EU, and CARI participation is funded by ESSL/ACD&TIIMES and EOL), The Ice in Clouds Experiment (ICE-L) campaign on the C-130 in November/December 2007, the GV instrument test flights (HEFT) in February, the Stratosphere-Troposphere Analyses of Regional Transport 2008 (START-08) mission in April-June (both on the GV) and the VAMOS Ocean-Cloud-Atmosphere-Land Study - RegionalExperiment (VOCALS-REx) experiment in October/November using the C-130 (all funded by NSF).

A project was initiated to characterize the accuracy and precision of several NCAR humidity sensors (including the CARI TDL GV-water vapor instrument) and our commercial humidity calibration system. This project will culminate in CARI participation in the European intercomparison experiment, AquaVit, in October, 2007 at the AIDA chamber of the Forschung Zentrum Karlsruhe, Germany. Additionally, this project is conducted in collaboration with the Technical University of Wiesbaden, and will result in a diploma thesis for our German student visitor, Dennis Kraemer. The CARI group provides the technical and educational oversight and mentoring, TIIMES provides visitor funds, and EOL provides hygrometric equipment and calibration systems.

CARI will provide measurements of water vapor (using the TDL H2O instrument), Fast-Ozone and CO for the ICE-L experiment in late fall of 2007. The objective of the ICE-L experiment is to show that under given conditions, direct ice nucleation measurement(s), or other specific measurable characteristics of the aerosol, can be used to predict the number of ice particles forming by nucleation mechanisms in selected clouds. The PIs also seek improved quantitative understanding of the roles of thermodynamic pathway, location within the cloud, and temporal dependency. CARI measurements of CO and ozone allow some level of air mass history information that will aid in interpretation of data from instruments characterizing aerosol and cloud composition and physics.

The 2-channel GV NO-NOy instrument will be reconfigured for flight on the NSF GV for testing in the HEFT test flights. The instrument was built in ACD and the final steps and design changes to achieve certification for use on the GV are being completed with the help of EOL funds. The HEFT flights will be the first flights of this new instrument on the GV and are an important prelude to participation in START08 in April-June 2008, where the NO measurements will be critical to the sampling of convective outflows, and the NOy will be valuable as a tracer for diagnosing transport processes in the UTLS.

The HAIS Fast-Ozone instrument will also be flown on START08, where the multi-scale dynamical control of the distribution of O3 and other species is a central focus. The instrument will be completed by the end of CY07 and it is planned to fly the Fast-Ozone instrument during the HEFT test flights in combination with the NO-NOy instrument using shared components to save rack space on the GV.

VOCALS-REx is an international field experiment designed to better understand physical and chemical processes central to the climate system of the Southeast Pacific (SEP) region. VOCALS-REx will focus on interactions between clouds, aerosols, marine boundary layer (MBL) processes, upper ocean dynamics and thermodynamics, coastal currents and upwelling, large-scale subsidence, and regional diurnal circulations, to the west of the Andes mountain range. Among expected outcomes are improved model simulations of the coupled climate system in both the SEP and over the wider tropics and subtropics. CARI will provide water vapor, CO, CO2, and ozone measurements to this project. The measurements will provide valuable tracer information for identifying sources of aerosols and gases in air masses transported off-shore from the South American continent contributing to the cloud chemistry and dynamics aspects of the experiment.

Data Analysis and interpretation

Work on field campaign data will continue including data quality control and archiving, data analysis and interpretation and presentation of results, with emphasis on the publication of MIRAGE and INTEX results as well as PACDEX, ACME and PASE data.