The Impacts of Marine Organic Emissions on Atmospheric Chemistry and Climate (Invited)

Using laboratory studies and global/regional climate model results, this talk will contribute to two main research questions: 1) what can be learned about the carbon emission inducing stress factors for marine algae, and 2) what is a potential impact of marine biogenic volatile organic compound (VOC) emissions on global atmospheric chemistry and climate. Marine photosynthetic organisms emit VOCs which can form secondary organic aerosols (SOA). Currently large uncertainty exists in the magnitude of the marine biogenic sources, their spatiotemporal distribution, controlling factors, and contributions to natural background of organic aerosols. Here laboratory results for the production of isoprene and four monoterpene (α-pinene, β-pinene, camphene and d-limonene) compounds as a function of variable light and temperature regimes for 6 different phytoplankton species will be discussed. The experiment was designed to simulate the regions where phytoplankton is subjected to changeable light/temperature conditions. The samples were grown and maintained at a climate controlled room. VOCs accumulated in the water and headspace above the water were measured by passing the sample through a gas chromatography/mass system equipped with a sample pre-concentrator allowing detection of low ppt levels of hydrocarbons. The VOC production rates were distinctly different for light/temperature stressed (the first 12 hour cycle at light/temperature levels higher than what the cultures were acclimated to in a climate controlled room) and photo/temperature-acclimated (the second 12 hour light/temperature cycle) states. In general, all phytoplankton species showed a rapid increase in isoprene and monoterpene production at higher light levels (between 150 to 420 μE m^-2 s^-1) until a constant production rate was reached. Isoprene and α-pinene, production rates also increased with temperature until a certain level, after which the rates declined as temperature increased further. Two modeling studies with the online emissions of marine isoprene/monoterpene and size-resolved marine primary organic aerosol have been carried out. The US EPA regional-scale Community Multiscale Air Quality modeling system was used to determine the impact of marine emissions on air quality, while the global-through-urban WRF/Chem model was applied to examine effect of ocean-derived trace gases and aerosols on chemistry-aerosol-cloud-climate interactions. With the isoprene reactions included in this study, the average contribution of marine isoprene to SOA and ozone (O₃) concentrations is predicted to be small, up to 0.004 μg m^-3 for SOA and 0.2 ppb for O₃ in coastal urban areas. When marine primary organic emissions are included, PM_2.5 levels can be increased by 0.1-0.3 μg m^-3 (up to 5%) in some coastal cities such as San Francisco, CA. Regionally, marine organics (primary and secondary) can cause up to 20% increase in surface cloud condensation nuclei concentration. Global effects on cloud droplet number and indirect forcing are predicted to be small, less than 1 cm^-3 and -0.1 W m^-2, respectively.