Abstract

Our traditional approach in combining measurements and models has been to measure one or more chemical species (we try to pick the important ones) and then comparing with model simulations. Another approach is to assimilate observed species, merging measurements and model chemistry-transport to produce a single, fully fleshed record of a species that merges the best and worst of its parents. A common weakness of these approaches is that they center on the static composition of the atmosphere rather than what is happening in the atmosphere to change composition, i.e., the chemical reactivity, the rates of production and loss of ozone and methane, which are not directly measurable.

The NASA Atmospheric Tomography (ATom) Mission was designed to go after the reactivity of the troposphere, identifying “Which Air Matters?” ATom completed its fourth and final deployment in May 2018. It has circumnavigated the global troposphere over 4 seasons. It has characterized the chemistry and transport history of the remote troposphere, through the Pacific and Atlantic Ocean basins, over Antarctica and the Arctic. Using the 10-second averages (2.5 km) with constant profiling from 500 ft to 12 km, ATom has collected chemical specification for over 120,000 air parcels, with enough information to be able to describe (with models) the subsequent 24-hour evolution of the parcel in terms of ozone and methane. This chemical climatology allows us to evaluate chemistry-climate models and identifies the ‘hot’ parcels that are driving the evolution of the troposphere. ATom also measured a climatology of photolysis rates that allows us to test the role of clouds in driving photochemistry and reactivity. This talk presents the strategy, design and some early results from the ATom models and measurements.

For an introduction to the approach and methodologies see the two pre-ATom papers: Atmos. Chem. Phys., 17(14), 9081-9102, doi: 10.5194/acp-17-9081-2017. “Global Atmospheric Chemistry – Which Air Matters” Atmos. Meas. Tech., 11, 2653–2668, 2018, doi: 10.5194/amt-11-2653-2018. “How well can global chemistry models calculate the reactivity of short-lived greenhouse gases in the remote troposphere, knowing the chemical composition,”