Chemical Ionization Mass Spectrometer

The CIMS instrument consists of a low pressure ion molecule reactor (IMR) coupled to a quadrupole mass filter by an actively pumped collisional dissociation chamber (CDC) and an octopole ion guide. The vacuum system is a 100 mm outer diameter stainless steel chamber evacuated with two small turbo pumps (70 l s-1). The mass filter is a set of 9.5 mm diameter quadrupole rods housed in the main vacuum chamber. The CDC is a short 80 mm diameter chamber that houses an octopole ion guide and is evacuated with a hybrid molecular drag pump. The IMR is evacuated with a scroll pump (300 l min-1) that also serves as the backing pump for the mass spectrometer.

Click here for the Collaborative Ground and Airborne Observations description page.

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DC-8 - AFRC, NSF G-V
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Chemical Ionization Mass Spectrometer

The single mass analyzer CIMS (S-CIMS) was developed for use on NASA’s ER-2 aircraft. Its first measurements were made in 2000 (SOLVE). Subsequently, it has flown on the NASA DC-8 aircraft for INTEX-NA, DICE, TC4, and ARCTAS, as well as on the NCAR C-130 during MILAGRO/INTEX-B. HNO3 is measured by selective ion chemical ionization via the fluoride transfer reaction: CF3O- + HNO3 → HF • NO3- + CF2O In addition to its fast reaction rate with HNO3, CF3O- can be used to measure additional acids and nitrates as well as SO2 [Amelynck et al., 2000; Crounse et al., 2006; Huey et al., 1996]. We have further identified CF3O- chemistry as useful for the measurement of less acidic species via clustering reactions [Crounse et al., 2006; Paulot et al., 2009a; Paulot et al., 2009b; St. Clair et al., 2010]: CF3O- + HX → CF3O- • HX where, e.g., HX = HCN, H2O2, CH3OOH, CH3C(O)OOH (PAA) The mass analyzer of the S-CIMS instrument has recently been upgraded from a quadrupole to a time-of-flight (ToF) analyzer. The ToF admits the sample ion beam to the ion extractor, where a pulse of high voltage orthogonally deflects and accelerates the ions into the reflectron, which in turn redirects the ions toward the multichannel plate detector. Ions in the ToF follow a V-shaped, 43 cm path from extractor to detector, separating by mass as the smaller ions are accelerated to greater velocities by the high voltage pulse. The detector collects the ions as a function of time following each extractor pulse. The rapid-scan collection of the ToF guarantees a high temporal resolution (1 Hz or faster) and simultaneous data products from the S-CIMS instrument for all mass channels [Drewnick et al., 2005]. We have flown a tandem CIMS (TCIMS) instrument in addition to the SCIMS since INTEX-B (2006). The T-CIMS provides parent-daughter mass analysis, enabling measurement of compounds precluded from quantification by the S-CIMS due to mass interferences (e.g. MHP) or the presence of isobaric compounds (e.g. isoprene oxidation products) [Paulot et al., 2009b; St. Clair et al., 2010]. Calibrations of both CIMS instruments for HNO3 and organic acids are performed in flight using isotopically-labeled reagents evolved from a thermally-stabilized permeation tube oven [Washenfelder et al., 2003]. By using an isotopically labeled standard, the product ion signals are distinct from the natural analyte and calibration can be performed at any time without adversely affecting the ambient measurement. We also fly calibration standards for H2O2 (evolved from urea-hydrogen peroxide) and MHP (from a diffusion vial).

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Airborne Compact Atmospheric Mapper

Two spectrographs + HD video camera

Air Quality (AQ) 304:520 nm 0.8 nm resolution (NO2, O3, UV absorbing aerosols, SO2, HCHO)

Ocean Color (OC) 460:900 nm 1.5 nm resolution

Video camera (2592x1936 pixels) –3 pixel FWHM

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Airborne Scanning Microwave Limb Sounder

The National Research Council decadal survey for earth science identified the need for a Global Atmospheric Composition Mission (GACM) to address crucial issues on how changes in atmospheric composition affect the quality and well-being of life on earth. The baseline GACM instrument suite comprises UV/Vis and IR/SWIR spectrometers and an advanced microwave limb sounder working together to retrieve atmospheric composition worldwide with high spatial resolution. The Scanning Microwave Limb Sounder (SMLS) is designed to meet the measurement requirements of GACM by providing complete orbit-to-orbit retrieval of O3, N2O, temperature, water vapor, CO, HNO3, ClO, and volcanic SO2 in the upper troposphere and lower stratosphere. Unlike previous MLS instruments that only scanned the limb vertically leaving large orbit to orbit gaps, SMLS will simultaneously scan both in azimuth and elevation providing complete global coverage with 6 or more repeat measurements per day. SMLS will employ extremely sensitive, broadband, sideband-separating, SIS receivers centered at 230 and 640 GHz that provide the same precision as those on Aura MLS with a 100 fold reduction in integration time. SMLS will use a novel antenna design that provides high vertical resolution and enables rapid horizontal scanning of the field of view.

Since the late summer 2008, the development of the SMLS instrument technology has been underway within NASA Earth Science Technology Office’s Instrument Incubator Program. The objective of this development is to advance the core signal path technologies required for a microwave limb sounder with the capability to map the composition of the upper troposphere and stratosphere with 50x50x1 km spatial sampling and six times daily mid-latitude repeat coverage. The specific goals of this effort include:

* the mitigation of the optics and calibration risks of the SMLS flight sensor design by constructing and testing an airborne prototype of the SMLS sensor and calibration system - A-SMLS - using prototype sideband-separating mixers, line sources, and advanced spectrometers and calibration targets;

* the mitigation of the development risks of the cryogenics system by developing a flight-like cryostat and demonstrating an end-to-end prototype of the SMLS signal path from the antenna interface through the back-end electronics, and quantifying its stability, calibration accuracy, linearity, and sensitivity; and

* the demonstration of the potential science measurement capability of SMLS through the A-SMLS science flights.

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