The Georgia Tech Laser-Induced Fluorescence instrument measures nitric oxide (NO), formaldehyde (HCHO), and nitrogen dioxide (NO2). Each species is measured by laser-induced fluorescence at reduced pressure. Ambient air is drawn in through a pinhole orifice into a pair of multipass White cells. The pressure in the White cells is maintained at 5-10 mbar to extend the fluorescence lifetime, and the multiple passes (typically 32-40) effectively extends the probe interaction volume. The ambient air is probed at 90o from the flow and the fluorescence collected at 90o to the flow and probe.
NO is probed at the 226 absorption line and monitored at the 247 nm fluorescence. The laser pulse and scattering will be time-gated out using microchannel plate detectors. The expected 2-sigma limit of detection is 5 pptv/min. Formaldehyde is probed at 353 nm and the fluorescence monitored in a range from 400 to 450 nm. The expected performance is 10 pptv/min. NO2 will be probed near 435 nm and the fluorescence around 780 nm collected. Its expected performance is 15 pptv/min. In each case, the probe wavelength will be alternately switched from the absorption feature to a nearby “off-line” position to determine the background. The actual frequency will be monitored in reference cells. Calbration is done by standard addition to the airflow. The light sources used are custom-built cavities pumped by a diode-pumped Nd:YAG laser operating at ~10 kHz.
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.
The instrument uses two-tone frequency modulation (TTFM) with signal detection at approximately equals 12 MHz. Multiplexing is achieved using a dichroic optical element and a mechanical chopper which blocks each beam alternately. A control program running on a dedicated digital signal processor (DSP) allows the registration of the full absorption line shape each millisecond and simultaneous zero overhead on-line data reduction using a multiple linear regression algorithm. Gas exchange through the compact multireflection cell (2.71 volume, total path 53 m.) takes place in approximately equals 200 ms and thus determines the instrument response time.
The Whole Air Sampler (WAS) collects samples from airborne platforms for detailed analysis of a wide range of trace gases. The compounds that are typically measured from the WAS includes trace gases with sources from industrial midlatitude emissions, from biomass burning, and from the marine boundary layer, with certain compounds (e.g. organic nitrates) that have a unique source in the equatorial surface ocean. The use of a broad suite of tracers with different sources and lifetimes provides powerful diagnostic information on air mass history and chemical processing that currently is only available from measurements from whole air samples. Previous deployments of the whole air sampler have shown that the sampling and analytical procedures employed by our group are capable of accessing the wide range of mixing ratios at sufficient precision to be used for tracer studies. Thus, routine measurement of species, such as methyl iodide, at <= 0.1 x 10-12 mole fraction, or NMHC at levels of a few x 10-12 mole fraction are possible. In addition to the tracer aspects of the whole air sampler measurements, we measure a full suite of halocarbon species that provide information on the role of short-lived halocarbons in the tropical UT/LS region, on halogen budgets in the UT/LS region, and on continuing increasing temporal trends of HFCs (such as 134a), HCFCs (such as HCFC 141b), PFCs (such as C2F6), as well as declining levels of some of the major CFCs and halogenated solvents. The measurements of those species that are changing rapidly in the troposphere also give direct indications of the age and origin of air entering the stratosphere.
In early 2000, the Ames Atmospheric Radiation Group completed the design and development of an all new Solar Spectral Flux Radiometer (SSFR). The SSFR is used to measure solar spectral irradiance at moderate resolution to determine the radiative effect of clouds, aerosols, and gases on climate, and also to infer the physical properties of aerosols and clouds. Additionally, the SSFR was used to acquire water vapor spectra using the Ames 25-meter base-path multiple-reflection absorption cell in a laboratory experiment. The Solar Spectral Flux Radiometer is a moderate resolution flux (irradiance) spectrometer with 8-12 nm spectral resolution, simultaneous zenith and nadir viewing. It has a radiometric accuracy of 3% and a precision of 0.5%. The instrument is calibrated before and after every experiment, using a NIST-traceable lamp. During field experiments, the stability of the calibration is monitored before and after each flight using portable field calibrators. Each SSFR consists of 2 light collectors, which are either fix-mounted to the aircraft fuselage, or on a stabilizing platform which counteracts the movements of the aircraft. Through fiber optic cables, the light collectors are connected to 2 identical pairs of spectrometers, which cover the wavelength range from (a) 350 nm-1000 nm (Zeiss grating spectrometer with Silicon linear diode array) and (b) 950 nm - 2150 nm (Zeiss grating spectrometer with InGaAs linear diode array). Each spectrometer pair covers about 95% of the incoming solar incident irradiance spectrum.
The SP2 is a laser-induced incandescence instrument primarily used for measuring the refractory BC (rBC) mass content of individual accumulation-mode aerosol particles. It is able to provide this data product independently of the total particle morphology and mixing state, and thus delivers detailed information not only about BC loadings, but also size distributions, even in exceptionally clean air. The instrument can also provide the optical size of individual particles containing rBC, and identify the presence of materials associated with the BC fraction (i.e. identify the rBC’s mixing state). Since its introduction in 2003, the SP2 has been substantially improved, and now can be considered a highly competent instrument for assessing BC loadings and mixing state in situ. NOAA deploys multiple SP2s with different designs: the first was built for the WB-57F research aircraft. Two others are rack-mounted units customized at NOAA; one of the rack mounted units can be humidified, and has been deployed with a paired dry rack-mounted SP2 as the "Humidified-Dual SP2" (HD-SP2). The rack mounted units are suitable for in-cabin operations.
The UC-Irvine research group collected whole air samples aboard the NASA DC-8 aircraft during the summer 2019 NASA Fire Influence on Regional to Global Environments Experiment - Air Quality (FIREX-AQ) field mission. More than 70 trace gases were identified and quantified at our Irvine laboratory, including C2-C10 NMHCs, C1-C2 halocarbons, C1-C5 alkyl nitrates, and selected sulfur compounds using our established technique of airborne whole air sampling followed by laboratory analysis using gas chromatography (GC) with flame ionization detection (FID), electron capture detection (ECD), and mass spectrometric detection (MSD). Our experimental procedures build on those that have been successfully employed for numerous prior NASA field missions, for example PEM Tropics A and B, TRACE-P, INTEX-A and B, ARCTAS, DC-3, SEAC4RS, ATom, KORUS-AQ, FIREX-AQ, and SARP.
The SAFS instruments determine wavelength dependent actinic flux from 280-420 nm. The actinic flux in combination with the absorption cross section and quantum yield molecular data will be used to calculate the photolysis frequencies of multiple photochemically important molecular processes, including O3, NO2, HONO, CH2O, H2O2, CH3OOH, HNO3, PAN, CH3NO3, CH3CH2NO3, and CH3COCH3.
The SAFS measurement is based on a 2p steradian hemisphere hemispherical quartz light collector, a double monochromator, and a low dark current photomultiplier. The monochromator employs dual 2400 G/mm gratings which produce a 1 nm FWHM spectral resolution and very low straylight. The instrument package on the aircraft includes two independent, but time synchronized (IRIG-B) spectroradiometer systems to measure the up- and down-welling fluxes in a 10 second scan time. Summing these produces the spherically integrated actinic flux.
POS AV is a hardware and software system specifically designed for direct georeferencing of airborne sensor data. By integrating precision GNSS with inertial technology, POS AV enables geospatial projects to be completed more efficiently, effectively, and economically. POS AV is engineered for aerial cameras, scanning lasers, imaging sensors, synthetic aperture radar, and LIDAR technology.
