2B: NASA ATom mission

The NASA Atmospheric Tomography mission (ATom) has a stated goal to identify and quantify human impacts on the chemistry of the remote atmosphere. ATom uses the highly instrumented NASA DC-8 platform as its primary tool and nearly pole-to-pole sampling of the atmosphere is being conducted as a series of four campaigns covering all four seasons. The campaigns consist of 11-13 research flights covering a wide longitudinal and latitudinal range (see Figure 1 below) and investigate the vertical chemical structure from 0-11 km in both the Atlantic and Pacific. Three of the four campaigns have now been completed and NCAR ACOM scientists have provided key data for all three: 1) spectrally resolved down- and up-welling in situ ultraviolet and visible actinic flux measurements from approximately 280-650 nm (Hall and Ullman, CAFS instrument) and 2) speciated measurements of a wide range of VOCs (Apel, Hornbrook, and Hills) using the Trace Organic Gas Analyzer (TOGA).

TOGA measures many chemical species including those emitted from industry, fires, transportation and the biosphere. One such chemical is dichloromethane (CH2Cl2), an ozone depleting substance that is emitted by industrial sources and is rapidly increasing in the troposphere. If sustained growth rate continues, some of the gains achieved by Montreal Protocol could be offset, further delaying the return of Antarctic ozone to pre-1980 levels.  High quality in situ TOGA CH2Cl2 measurements of the most remote troposphere from the surface to the lower stratosphere are being recorded to complement the NOAA surface data and gain insight into its transport pathways, gradients, and especially its sources. Figure 1a shows the NASA DC-8 flight track for the ATom-1 campaign colored by TOGA measured CH2Cl2. Since this chemical has a lifetime on the order of inter-hemispheric mixing, a strong gradient exists between the northern (NH) and southern hemispheres (SH) with much higher concentrations in the NH, which is evidence of a NH source. Figure 1b shows CH2Cl2 measurements versus altitude and colored by longitude. The highest values are found in the most western latitudes which indicates that there are significant sources in Asia. It is important that these sources be identified and brought to the attention of the governments ultimately responsible for controlling emissions.

Figure 1. a)  NASA ATom-1 flight track colored by TOGA dichloromethane concentration.
Figure 1. a)  NASA ATom-1 flight track colored by TOGA dichloromethane concentration. Markers are scaled with altitude with larger markers signifying lower altitude; b) TOGA dichloromethane vs. altitude colored by longitude.