Contrasting aerosol regimes and radiative forcing across the Andean–Amazonian transition: A seven-year analysis of biomass burning impacts

Abstract

Biomass burning in the Amazon Basin is a major source of atmospheric aerosols affecting regional climate and air quality across tropical South America, yet the contrasting impacts on high-altitude Andean and lowland Amazonian environments remain poorly quantified. Here we present a seven-year (2015–2021) integrated analysis of aerosol transport pathways, composition, and radiative forcing at two contrasting receptor sites: Huancayo Observatory (3313 m a.s.l.) in the Peruvian Andes and Rio Branco (212 m a.s.l.) in the southwestern Brazilian Amazon. By combining AERONET Level 2.0 observations, HYSPLIT backward trajectories, VIIRS-SNPP active fire detections, and MERRA-2 speciated aerosol products, we identify two fundamentally distinct aerosol regimes within the same regional system. Rio Branco experiences direct, near-field exposure (<200 km) to intense biomass burning during June–October, with extreme aerosol loading (AOD440 up to 1.25; PM2.5 exceeding 50μg m−3), pronounced organic carbón dominance (>90% of PM2.5), and atmospheric radiative forcing of +75 W m−2 during the SON peak—among the highest reported for Amazonian biomass-burning conditions. In contrast, Huancayo receives diluted, aged smoke via long-range transport (300–600 km), with mixed composition including persistent mineral dust (18%–30%) and sulfate (12%–23%), and a substantially lower atmospheric forcing of +33 W m−2. The resulting 2.3-fold inter-site difference in atmospheric radiative forcing, robust within an SSA-perturbation uncertainty envelope, illustrates how source proximity and topographic barriers jointly modulate aerosol–climate interactions across the Andean–Amazonian transition zone, with implications for regional circulation, precipitation feedbacks, and Andean cryosphere stability.