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Impact of African Dust, Biomass Burning, and Other Air Mass Types on Cloud Condensation Nuclei Concentrations at a Coastal Location in the Southeastern United States
EVA-LOU EDWARDS, Andrea F Corral, Hossein Dadashazar, Paquita Zuidema, Cassandra Gaston, Anne Barkley, Armin Sorooshian, University of Arizona
Abstract Number: 205
Working Group: Aerosols, Clouds and Climate
Abstract
This study investigates the influence of different air mass types, including African dust and biomass burning (BB), on cloud condensation nuclei (CCN) concentrations at 0.2% (CCN0.2%) and 1.0% (CCN1.0%) supersaturation (SS) in Miami, Florida. Based on ground site measurements, CCN0.2% and CCN1.0% concentrations were 373 ± 200 cm-3 and 584 ± 323 cm-3, respectively, on days with minimal presence of African dust and BB (i.e., background days). In contrast, CCN concentrations were not elevated on days with highest influence of African dust (289 ± 104 cm-3 [0.2% SS] and 591 ± 302 cm-3 [1.0% SS]). However, CCN concentrations were substantially enhanced on days with the greatest impact from BB (1408± 976 cm-3 [0.2% SS] and 3337 ± 1252 cm-3 [1.0% SS]). Ratios of CCN0.2%: CCN1.0% were used to compare the hygroscopicity of the aerosol associated with African dust, BB, and background days. Average ratios were similar for days impacted by African dust and BB (0.54 ± 0.17 and 0.55 ± 0.17, respectively). A much higher average ratio was observed on background days (0.71 ± 0.14), owing in part to a strong presence of sea salt and reduced presence of more hydrophobic species such as those of a carbonaceous nature. Finally, periods of heavy rainfall were shown to effectively decrease both CCN0.2% and CCN1.0% concentrations, although the rate at which such concentrations increased after the rain varied. This work contributes knowledge on the nucleating ability of African dust and BB after varying periods of atmospheric transport (days to weeks), which can lead to improvements in model predictions for CCN concentrations in comparable situations.