Book Description
Aerosols can interact with radiation directly through scattering and absorption and indirectly by serving as cloud condensation nuclei. The uncertainty of how particles and clouds interact with radiation is still high amidst the progress made in recent years, which hinders our current understanding of how these particles affect the Earth’s radiation budget. This works aims to reduce this uncertainty by targeting the two most light-absorbing atmospheric particles, mineral dust and black carbon, and study how they interact with radiation, how they serve as cloud condensation nuclei, assessing popular measurement techniques and evaluating their impact in two different tropical forest ecosystems. Field measurements were carried out in the Caribbean island of Puerto Rico and in the Brazilian Amazon. In Puerto Rico, aerosol-cloud interactions were studied in the tropical montane cloud forest (TMCF) of Pico del Este, which receives consistently during summer months the influence of mineral dust from the Sahara/Sahel region in Africa (i.e., African dust). In Brazil, specifically in the Amazon basin, measurements of black carbon were performed in the city of Manacapurú, an area exposed to the influence of urban and biomass burning pollution. At Pico del Este, periods of low and high dust influence were identified through the use of aerosol optical properties, and air mass trajectories (HYSPLIT). It was found out that African dust interacts with clouds and produces a higher number of droplets, but the mean droplet effective diameter is not significantly altered. Similarly, the deposition of water and nutrients through water and clouds was studied, and results suggests that rain is the main mechanism through where water is deposited to the ecosystem over clouds (58- 78%). Cloud water presented an enrichment of nutrients over rainwater, suggesting that clouds are more important than rain for supplying TMCFs with nutrients. At the Brazilian Amazon basin, an Aethalometer -the most popular technique for measuring black carbon concentrations through the absorption coefficient- was used and several corrections used to overcome known artefacts for this type of measurements were evaluated. Results suggests that this technique can overestimate the absorption coefficient by a factor of 5 and that the corrections do not agree well among each other.