Sea spray and the atmospheric transport of nonylphenol ethoxylates. A combined laboratory, field and modeling study

Abstract

Nonylphenol ethoxylates (NPEOs) are environmentally ubiquitous non-ionizing surfactants that show a preference for the air–water interface. They are therefore potentially subject to enhanced transport by aqueous aerosols. The extent to which aqueous aerosols affect the overall environmental fate and behavior of NPEOs is investigated with a combination of laboratory and field experiments and mathematical modeling. Aqueous aerosol droplets were generated in a laboratory-based experimental system. Aqueous aerosols were measured to have concentrations of NPEOs at least four times greater than in the bulk source water.The concentration of nonylphenol and nonylphenol monoethoxylate in aqueous aerosols off the coast of Bermuda were 4.3–19.2 times higher than in coastal water and open water collected from the Bermuda Atlantic Time Series sampling site. Coastal water showed higher concentrations than open water samples ranging from 36 to 51 ng L−1 and 14 to 21 ng L−1 respectively. Depth profiling showed a loss of detection below 300 m. Aqueous aerosol enrichment was demonstrated and relative atmospheric concentrations ranged from 0.28 to 1.8 ng m−3. A generic marine model was developed using independent North Sea data to estimate the relative potential for NPEO transfer within spray droplets to the atmosphere and subsequently into the gas phase by volatilization. The results were compared to the estimated direct volatilization from the surface of a natural water body. The upward mass flux of NPEOs by direct volatilization was comparable in magnitude to the fluxes due to spray generation, depending on the wind speed and droplet sizes. The experimental results and the model calculations were illustratively applied to reported NPEO concentrations in the North Sea. Aerosol generation provides a feasible mechanism for atmospheric transport of NPEOs and their degradation products, nonylphenols (NPs).