Abstract ID: 243

Influence of the Manaus City plume on Amazon green ocean air: ozone production, precursor sensitivity and aerosol load

The temporal and spatial dynamics of the urban plume of Manaus City were investigated in the dry-to-wet transition period in 2001, as a contribution to the LBA-CLAIRE airborne field campaign. The flight patterns comprised vertical profile measurements and crosswind transects at different distances downwind of Manaus, including O3, NO, NO2, CO, VOC, CO2, and H2O. Aerosol loads were characterized by total aerosol number concentration (CN) and effective cloud condensation nuclei (CCN). Within the plume CN/CO ratios were about an order of magnitude higher than observed in Amazon biomass burning plumes. While in the background atmosphere a very large fraction of CN serves as CCN (30-50% at 0.6% supersaturation), CCN/CN ratios observed within the plume indicated that less than 10 % of particles acted as CCN. The footprint of Southern Manaus City was characterized by strong NOx emissions, suggesting a major contribution of ~1.5 kg day-1 of NOx by power plants. Observation-based estimates of the ozone production rates within the plume were up to 15 ppb h-1. This is in good agreement with production rates simulated by a single column chemistry and transport model (SCM), which has been applied to interpret the temporal and spatial chemical evolution of the Manaus plume and to assess the potential impact of the pollution on ecosystems downwind. In the near vicinity (<50 km) of Manaus, the strong power plant NOx sources result in a titration of ozone compared to the residual urban plume, while at greater distance the power plant emissions give rise to strong enhancements of ozone mixing ratios. The simulated N-deposition downwind of the Manaus plume is as high as ~70 kg N ha-1 yr-1 close to Manaus, decreasing to about 30 kg N ha-1 yr-1 at a distance of about 1500 km, which indicates that the Manaus plume can have a profound impact on ecosystem functioning far downwind from the source area.

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

Presentation Type:  Poster