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

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).