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Improved method for quantifying the air-sea flux of volatile and semi-volatile organic carbon

Emily J. Hauser, Rebecca M. Dickhut, Renee Falconer, Andrew S. Wozniak

Limnol. Oceanogr. Methods 11:287-297 (2013) | DOI: 10.4319/lom.2013.11.287

ABSTRACT: A method for quantifying the diffusive air-sea exchange of gaseous organic carbon (OC) was developed. OC compounds were separated into two operational pools -those that were kinetically air limited in diffusion across the air-sea interface and those that were water limited - during simultaneous air/water sampling. The method separates OC compounds into low Henry's law constant (low-H) semivolatile OC (SOC) and high Henry's law constant (high-H) volatile OC (VOC) pools that can be categorized by relating diffusion kinetic parameters to Henry's Law constant. Air limited (low-H; H << ~0.1 L atm mol-1) compounds were collected in pure water traps and were quantified as dissolved OC, whereas water limited (high-H; H >> ~0.1 L atm mol-1) compounds were collected on solid sorbent tubes downstream from the water traps and were analyzed by gas chromatography-flame ionization detection (GC-FID). Separating OC based on H, rather than measuring OC as one bulk pool, allows improved estimates of OC concentration gradients and fluxes. A 10-month field study in the York River Estuary in Gloucester Point, VA revealed an average VOC flux of 138 μg C m-2 d-1 and an average SOC flux of 832 mg C m-2 d-1 (positive fluxes denote sea to air transfer).