Raman Microspectroscopy: Surveying Phytoplankton Bloom Emissions and Their Effect on Seeding Clouds

Aerosols emitted from phytoplankton blooms contribute to cloud seeding and climate modulation. Currently, the role of a phytoplankton bloom in producing emissions to produce aerosols for cloud formation is not yet understood. Additional research is needed to quantify the actual impact of a phytoplankton bloom on producing atmospheric aerosols which are able to seed clouds. Therefore, the laboratory mesocosm experiment was designed to sample aerosols from a tank that simulated conditions at sea during the life cycle of a phytoplankton bloom (T. Wessflogii). The experiment took place over seventeen days. Aerosol particles were collected through cascade impactors (PIXES). A Thermo Nicolet DXR Raman microscope (controlled by Omnic software) was used to evaluate the composition of these particles. The diameters of the particles used in this experiment were 1-8 μm(supermicron size) and 0.06-1 μm (submicron size). Aerosol samples in both size ranges were collected during four stages of the phytoplankton bloom: growth phase, stationary phase, early death phase, and late death phase. The Raman microscope can be used to generate a map that captures several spectra from different locations on one particle. Composition maps were produced for each supermicron and submicron sample. Then, each peak, or Raman shift, detected from the spectral map was analyzed to determine composition. The preliminary results of analyzing spectra show that there is a recurring peak around 518-520 cm^-1 which indicates silicon dioxide. Preliminary results also show that the chemical composition of the phytoplankton bloom shifts during its life cycle. At the end of the phytoplankton’s life cycle, the concentration of submicron sized particles seemed to increase slightly. This could be attributed the particles’ compositions; however, no direct correlation has been found at this time. Further analysis of the spectra is ongoing.