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TG-01 Abstract

Cooperative Regional Transport Modeling of C and N for Amazonia

Robert B. Chatfield — NASA/HQ and Ames (US-PI)
Maria AssunšŃo Faus da Silva Dias — IAG/USP (SA-PI)

Hypotheses and Cautions

We assert several points about the atmospheric environment of LBA-ECO, which appear

reasonable. Only newly funded work under LBA-ECO will allow us to test these and to

aid the ecological community with their interpretation of atmospheric concentrations of CO2,

CO, CH4, N20, and aerosols, as well as assessments of carbon loss

from Amaz˘nia.

1. The atmospheric environment of the LBAE study area will be affected by inflow of

outside air in the lower troposphere, and the inflow will be greatest during the rainiest

seasons. These will at least dilute the concentrations of trace species like nitrous

oxide, methane, isoprene carbon monoxide natural particulate matter, etc. The rainy season

period will also be the period of the most dramatic vertical stirring, e.g., by cloud

downdrafts, with similar effects. See also the MTPE proposal, attached, especially the

front page, showing strong effects even during the dry season.

2. Composition of the inflow air is complex. For example, in March and April, there is

inflow of air from clean ocean regions to portions of Amaz˘nia. However, significant

inflow from northernmost South America and the Caribbean, and also more southern regions

of South America occurs. All these regions have burning or industrial pollution during

these times. The largest potential inflow of complex, polluted, air is, however, from

nearby subSaharan Africa, which is at the height of its burning season. As the preliminary

work of the citation indicates, these effects may be sporadic and poorly quantified at

this point, but are not to be neglected.

3. The loss of isoprene and other organics from the Amaz˘nian system provides a gross

loss of C from the system, 1.5% to 4% of NPP. Such percentage affects the perception of an

agrading ecosystem when periods of 25 to 100 years are considered. CO may constitute 15%

to 60% of the "final" products of isoprene oxidation; here, final means that the

material can escape the Amaz˘nian region. Other species may rapidly stick to surfaces or

be rained out, possibly somewhat downwind. Measurements of CO and organic trace gases in

CLAIRE and organic aerosols and condensibles by Paulo Artaxo at various times will inform

our estimates of C loss from Amaz˘nia.

Abstract of Proposed Work

We propose to:

1. Compare and improve simulations of the chemical composition of the troposphere over

Amaz˘nia as made by American and Brazilian scientists using meteorological mesoscale and

larger scale models. USP and Ames scientist have selected past periods of intensive

measurement for intercomparison (e.g.. SCARB and ABLE periods). One focus of this work is

to compare quantitatively the effects of parameterizations of planetary boundary layer and

cloud venting.

2. Allow inferences of the perturbation of the Amaz˘nia lowermost troposphere by

outside influences. We will use incisive tracer simulations to highlight expected

perturbations on methane, nitrous oxide. Since effects on these long-lived species will be

small, and small concentration differences due to transport may nevertheless be used to

infer large effects, we will also simulate carbon monoxide, smoke aerosol mass, and

perhaps NO / N02. In addition to the climatic interest in these species, they

highlight exchange processes in great detail, and some of these species may be remotely


3. As measurements accumulate during the LBA period, we expect we can start studies

describing the role of isoprene, other non-methane arboreal emissions, and their products

on the carbon balance of Amaz˘nia. These studies serve two purposes: they help define the

CO export from that rainforest region to the world during seasons of low worldwide

burning, and they affect the Amaz˘nian C and N budgets at a significant level. This level

of funding does not allow chemical mechanistic studies of isoprene's return to the

ecosystem, but it does allow:

  • Initial studies of the isoprene profiles and concentrations using planetary boundary

    layer 1d models and thus some information on the isoprene flux from a forest and the

    location of the "stickiest" gases and aerosols relative to forest surfaces.

  • Large-scale studies of carbon flux from the Amazon based on estimated conversion

    efficiencies to CO, generically "sticky" organics, or aerosols.

  • Comparisons of observations and measurements will occupy later years of the

    proposal. Any students involved will need to familiarize themselves with the modeling and

    chemistry from an early stage of the LBA-E program cycle.


Last Updated: September 1998

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