Airborne flux measurements of trace species in an Arctic boundary layer

Abstract

In situ airborne measurements of the turbulent flux and mean values for O3, CO, and CH4 were obtained in the boundary layer over selected wetland systems in Alaska. These measurements were obtained in July–August 1988 as part of the NASA Global Tropospheric Experiment Program's Arctic Boundary Layer Expedition (ABLE 3A). The flux measurements obtained from this study provide information on the source/sink distribution of O3 and CH4 over the Yukon‐Kuskokwim Delta (YKD) and Alaskan North Slope (ANS) regions of Alaska. The source/sink distribution over the YKD is qualitatively correlated with surface vegetation type, identified from multispectral scanner imagery. Direct measurements of the spatial variation in the CH4 source strength were obtained over the YKD. The CH4 source strength over the YKD ranged from 25 to 85 mg m−2 d−1 during a flux survey flight which spanned a considerable portion of the YKD. A spatially averaged, seasonally adjusted source strength of 51 mg m−2 d−1 was established for the YKD. Indirect CH4 flux estimates obtained over the ANS indicate a much lower (∼10 mg m−2 d−1) source strength. The global CH4 emissions from tundra were estimated to be 44 Tg/a based on (1) the spatially averaged source strength obtained over the YKD, (2) current estimates of the global coverage of tundra, and (3) assuming a similarity between other tundra areas and that of the YKD. This estimate is taken to be an upper limit due to possible sampling inadequacies and because the spatial distribution of the CH4 source function over the YKD may not extend to all other northern wetland regions. This estimate is, however, in reasonable agreement with previous estimates. Airborne CO flux measurements over the YKD indicated low negative flux values over the coastal areas, while some positive fluxes were observed in the inland, sparsely forested regions. An inspection of the cospectrum of CO with vertical velocity for sample runs in coastal areas indicated a minimum at wavelengths which were noticeably shorter (70–400 m) than where any prominent feature could be found for similar cospectrums of heat, moisture, O3, or CH4 with vertical velocity. Similar analyses for transects over inland areas indicated occasional peaks in this same, short wavelength band. These features indicate the possibility of in situ photochemical destruction/production of CO, although the identification of a possible chemical mechanism was not attempted at this time. Tundra surfaces are estimated to be responsible for ∼32% of the total deposition loss of O3 poleward of 60°N. Data from the airborne O3 flux measurements made during this study indicate similar values of Rc for the ANS and YKD regions.

Soils as sources and sinks for atmospheric methane

“…It showed the kind of spatial flux variations that can be obtained at the regional scale. A comparison with chamber methane fluxes scaled-up using satellite imagery (Bartlett and Harriss 1993) gave a similar spatial integrated value for the summertime period to the one found by Ritter et al (1992) on 9 August 1988. Crill (1991) measured the seasonal pattern of methane consumption of a temperate woodland soil, using closed chambers at the same location.…”

“…1995, personal communication). Ritter et al (1992) did a survey flight over Alaska's Yukon-Kuskokwim Delta, from which they were able to extrapolate a contour-plot of methane flux superimposed to the land cover types. It showed the kind of spatial flux variations that can be obtained at the regional scale.…”

“…For ground-based operation, a vibrationfree environment can be relatively easily maintained, while for airborne operation the noise level is considerably higher. Only the NASA Electra aircraft equipped with a TDL having a 10-m folded optical path has reported methane fluxes measured by eddy-covariance (Ritter et al 1992 to EC for measuring turbulent methane flux in the mixed layer with an aircraft is to sample using the REA technique and analyze afterwards the air samples in differential mode using either a ground-based TDL or gas chromatograph fitted with a flame ionization detector (GC-FID). A GC-FID having a column with Pt catalyst to remove non-methane hydrocarbons by combustion has been described by Tohjima and Wakita (1994).…”

Seasonal and diurnal variation in CO fluxes from an agricultural bioenergy crop

“…However, the high variation between CO uptake and emission rates does not yet allow us to classify the ecosystem types or climatic regions. Tall tower (Andreae et al, 2015) and airborne measurements have indicated source areas of CO both in the Amazon basin (Harriss et al, 1990) and in the North American tundra (Ritter et al, 1992(Ritter et al, , 1994 suggesting a connection between high plant biomass and biological CO forming processes.…”

The NASA Carbon Airborne Flux Experiment (CARAFE): instrumentation and methodology

“…Airborne EC has elucidated surface-atmosphere exchange processes for more than 3 decades (Dabberdt et al, 1993;Desjardins et al, 1982;Lenschow et al, 1981;Ritter et al, 1992Ritter et al, , 1994Ritter et al, , 1990Sellers et al, 1997). Recent GHG applications include evaluations of net ecosystem exchange (NEE) over complex ecosystems (Miglietta et al, 2007;Zulueta et al, 2013) and quantification of CH 4 emissions from shale gas production regions , agricultural areas (Desjardins et al, 2018;Hiller et al, 2014), and Arctic biomes (Sayres et al, 2017).…”