Nitric oxide (NO) mixing ratio above the canopy in the Amazon rainforest (ATTO site)

Nitrogen oxides (NOx = nitric oxide (NO) and nitrogen dioxide (NO₂)) play a crucial role in atmospheric chemistry by influencing the concentrations of ozone (O₃) and hydroxyl radicals (HO_x = OH and HO₂), which are key oxidants in the atmosphere. In pristine ecosystems, these oxidants interact with biogenic volatile organic compounds (BVOCs) like isoprene, leading to the production of oxidized secondary organic compounds. Subsequent reactions with NO_x contribute to nitrate formation, which enhances particle growth and cloud condensation nuclei activity. This underscores the significance of NO_x even in regions with low atmospheric concentrations.

At the Amazon Tall Tower Observatory (ATTO), located in the central Amazon rainforest, we monitor NO and O₃ in a pristine tropical environment. Our study focuses on measurements from a walk-up tower at 40 m, but also a first look into NO and O₃ mixing ratios collected at multiple heights ranging from 5 cm to 79 m, covering the vertical profile above and below the canopy (canopy height is approximately 36 m). We analyze diurnal and nocturnal variations at 40 m and seasonal differences between the wet and dry periods to hint at how much NO is coming out of the canopy and its role in this unique ecosystem.