Biosphere-atmosphere Exchange of NOx, CH4, and O3 in Central Amazonia

The Amazon Forest has a unique combination of vegetation with diverse characteristics, climate, and a dynamic land use, factors that altogether govern the emission and fate of trace-gases and control particle formation and atmospheric chemistry. A better understanding of the interactions among the mechanisms that govern local emissions will lead to a better description of the local atmospheric chemistry, which have regional and global impacts. As part of the Green Ocean Amazon (GOAmazon) project, an array of complementary measurements is being conducted in a research site located near km 67 of BR163 highway, southeast of the city of Santarem (PA, Brazil), inside the Tapajos National Forest. The site where the measurements are being taken is surrounded by intact rain forest in a 6 km radius, and a ~45 m closed canopy. Measurements of fluxes and vertical profiles of NO, NO2, O3, CH4, and SO2 were added to the tower measurements in mid 2014. SO2 concentrations were below 0.1 ppb in the dry season of 2014, suggesting a negligible influence of anthropogenic sources of sulfur species at this site. Preliminary results show no significant seasonality in the daytime and nighttime O3 vertical profiles, although O3 daytime maximum values increased from 15 ppb in the wet season to 25 ppb in the dry season, on average. Occasionally, nighttime profiles showed relatively high O3 concentrations at levels below canopy, even near the ground. It is possibly caused by the breaking of nocturnal atmospheric stability, possibly associated with the subsidence of O3 enriched air masses from the free troposphere to the nocturnal boundary layer. NO soil emissions are indicated by concentrations in the ppb range for lower profile levels, and concentrations decreasing to a few hundreds ppt above the canopy.