Long-term measurements of aerosol optical properties and radiative forcing (2011-2017) over Central Amazonia

The Amazon region is one of the most pristine continental areas whose concentrations of atmospheric trace gases and aerosol particles are very low, mainly in the wet season. This study provides observational results of aerosol optical and radiative characteristics in situ as well as atmospheric columnar at a pristine forest in Central Amazonia. Spectral variation of the aerosol properties (aerosol optical depth [AOD], single scattering albedo [SSA], and asynunctry parameter [AP]) was evaluated using the AErosol RObotic NETwork (AERONET) data. The SSA values under natural atmospheric column conditions (AERONET) were compared to the SSA values calculated with in situ measurements. The values of shortwave aerosol radiative forcing (SWARF) on top of the atmosphere (TOA) and the surface (SUR) were estimated using the SBDART model and were validated with the AERONET values with regression analysis. SWARF had a high correlation to TOA (0.97) and SUR (0.92), including dry and wet seasons. Monthly, seasonal and annual mean values of SWARF(TOA) and SWARF(SUR) were negative while SWARF(ATM) values were positive. SWARF(TOA) was -9.18 +/- 2.80 W m(-2) and SWARF(SUR) was -20.77 +/- 5.04 W m(-2) in the dry season, inducing a heating rate (HR) of 0.37 +/- 0.13 K.day(-1). This study showed that, for a long series of measurements, the effects caused by aerosols on the radiative flux in the pristine forest of Central Amazonia were of the order of SWARF(TOA) of -3.66 +/- 1.59 W m(-2) and SWARF(SUR) of -11.86 +/- 2.35 W m(-2) during the wet season.