Abstract ID: 413

Seasonal variability in CO₂ and CO gradients across the Amazon

Carbon Monoxide (CO) plays a major role in controlling the global levels of OH in the atmosphere, and is a tracer of combustion, and product of hydrocarbon oxidation. Carbon dioxide (CO₂) is emitted by biological processes, respiration, as well as combustion and is absorbed by photosynthesis. Both of these gases have been measured at a forested site near Santarem, Para, Brazil (km67 tower site) - since 2001- , and at a coastal site, Maxaranguape, north of Natal - since 2002. Air at the Maxaranguape site is generally representative of tropical marine air that is transported into the Amazon by easterly tradewind flow, but there is not always direct transport between the sites. Analysis of concentration gradients observed between the two sites helps constrain estimates of the large-scale sources and sinks of these important carbon-containing gases. Mid-day mean concentrations of CO at km67 site range from a minimum of 66 ppb in May-June, at end of wet season, to a maximum of 400 ppb at peak of local burning season in November. Mid-day CO concentrations at the coastal site range from 40 to 100 ppb without a distinct seasonal cycle. The concentration gradient between the sites exceeds 100 ppb during October and November due to widespread agricultural burning. When there is little burning from January - June, CO concentrations at the km67 site exceed the coastal concentration by 20 - 40 ppb, supported in part by oxidation of biogenic hydrocarbons. CO₂ at the forested site has high concentrations at night as respiration and combustion CO₂ accumulate in stable surface layer and minimum concentrations in the mid afternoon when strong CO₂ uptake and dilution by vertical mixing combine to reduce CO₂ in the surface layer. Excluding local sources in nighttime land breezes CO₂ concentrations at the coastal site have very weak diel cycle. The median value of mid-day CO₂ concentration above the forest canopy (378 ppm) is slightly less than the median CO₂ concentration in air coming off the ocean at Maxaranguape (380.6 ppm).

Session:  Biogeochemistry - Sources, sinks, and atmospheric chemistry of trace gases.

Presentation Type:  Poster