Airborne Study Surveys Greenhouse Gases in World Tour
The first deployment of one of NASA's most ambitious research studies of Earth's atmosphere will take place this July and August. The Atmospheric Tomography mission will take off aboard the agency's DC-8 flying laboratory on a 26-day journey from the North Pole down the Pacific Ocean to New Zealand and then across to the tip of South America and back north up the Atlantic Ocean to the Arctic.
In Situ Measurements of Aerosol Microphysical Properties
Two instruments,a nucleation-mode aerosol size spectrometers (NMASS; Williamson et al., 2018), and an ultra-high sensitivity aerosol spectrometers (UHSAS; Kupc et al., 2018) comprise the AMP package for ACCLIP. The AMP package provides particle size distributions with up to one-second time resolution for dry aerosol particles between 0.003 and 1.5 µm in diameter. Details of methods, uncertainties, and data products from the AMP package are in Brock et al. (2019).
During ATom, the instruments were used to investigate how particles in the remote atmosphere influence climate by examining the origin of small particles in the remote atmosphere and their growth to sizes where they can affect clouds and the sources, characteristics, and distribution of soil dust and sea-spray particles, and 3) the importance long-range transport from human and natural sources on background aerosol properties.
The PFP whole air sampler provides a means of automated or manual filling of glass flasks, twelve per PFP. The sampler is designed to remove excess water vapor from the sampled air and compress it without contamination into ~1-liter volumes. These flasks are analyzed at the NOAA’s Global Monitoring Division laboratory for trace gasses and at the INSTAR’s Staple Isotope Lab laboratory for isotopes of methane. More than 60 trace gases found in the global atmosphere can be measured at mole fractions that range from parts-per-million (10-6), e.g., carbon dioxide, down to parts-per-quadrillion (10-15), e.g., HFC-365mfc. The chemical species monitored include N2O, SF6, H2, CS2, OCS, CO2, CH4, CO, CFCs, HCFCs, HFCs, Solvents, Methyl Halides, Hydrocarbons and Perfluorocarbons.
Medusa collects 32 cryogenically dried, flow and pressure controlled samples per flight. The samples are collected by an automated sampler into 1.5 L glass flasks that integrate over 25-s (1 e-fold) periods. Medusa provides discretely-sampled comparisons for onboard in situ O2/N2 ratio and CO2 measurements and unique measurements of Ar/N2 and 13C, 14C, and 18O isotopologues of CO2. The complementary measurements allow ground-truthing of onboard instrument measurements in a laboratory setting, where analysis conditions can often be more stringently controlled and carefully monitored. Isotope and argon measurements can provide additional information about land and ocean controls over the carbon cycle, and about the age and source of the air sampled.
Medusa consists of an onboard computer, two pressure controllers, two pumps, three multi-position selector valves, and a host of other hardware that control and direct the air samples. All air is dried by passing it through traps immersed in a -78 C dry ice bath, adjusted to match atmospheric pressure at sea level, and then automatically isolated in a flask. Medusa flasks are analyzed on a sector-magnet mass spectrometer and a LiCor non-dispersive infrared CO2 analyzer by the Scripps O2 Program at Scripps Institution of Oceanography.
The NCAR Airborne Oxygen Instrument measures O2 concentration using a vacuum-ultraviolet absorption technique. AO2 is based on earlier ship-board and laboratory instruments using the same technique, but has been designed specifically for airborne use to minimize motion and thermal sensitivity and with a pressure and flow controlled inlet system. To achieve the high levels of precision needed, AO2 switches between sample gas and air from a high-pressure reference cylinder every 2.5 seconds. Atmospheric O2 concentrations are typically reported in units of one part in 1,000,000 relative deviations in the O2/N2 ratio, which are referred to as "per meg." AO2 has a 1-sigma precision of ± 2 per meg on a 5 second measurement. For comparison, this is equivalent to detecting the removal of one O2 molecule from 2.5 million molecules of air. At typical flight speeds of 300 kts or climb/descent rates of 1500 fpm, 5-seconds correspond to a horizontal resolution of 750 m and a vertical resolution of 40 m. The instrument includes an internal single-cell CO2 sensor (LI-840), which is used to correct the O2 measurements for dilution by CO2 and for scientific purposes. To minimize inlet surface effects, the pressure in the inlet line is actively controlled at the aircraft bulkhead. The sample air is cryogenically dried in a series of electropolished stainless steel traps immersed in a dry ice Fluorinert slurry. The AO2 system consists of a pump module, a cylinder module, an instrument module, and a dewar.
New Mission to Provide Snapshot of ‘Average’ Atmosphere
A new NASA Earth Venture mission called the Atmospheric Tomography Mission (ATom) aims to provide a snapshot of the average atmosphere. ATom will systematically measure reactive gases and aerosols over the Atlantic and Pacific Oceans, where the atmosphere is relatively clean and sensitive to change.
