Sea spray aerosols (SSA) are released into the atmosphere as tiny "seawater droplets" due to bubble bursting on the ocean surface caused by winds and waves. Since oceans cover approximately 71% of the Earth's surface, sea spray aerosols contribute the largest natural aerosol source and hence, significantly influence the radiation balance and cloud microphysical properties. However, the high sensitivity of their formation to environmental conditions leads to significant uncertainties in global climate predictions.

Sea spray aerosol

The size and chemical composition of aerosols largely determine their atmospheric behavior. For SSA, their particle size distribution depends on the size distribution of the bubbles and their breakup mechanisms. Although SSA are directly produced from the ocean, their chemical composition differs from that of seawater. This is because bubble movement and bursting in seawater involves multiple air-water interfaces, where fractionation of organic matter and salts can occur. Therefore, environmental factors that influence the bubble breakup process will have a significant impact on the formation of SSA.

Sea surface temperature

Seawater surface temperatures globally range from -2 to 35 ℃, which could potentially affect seawater physicochemical properties and SSA formation. However, the dominant influence of wind speed on the formation of SSA in the marine boundary layer has limited the in-depth exploration of temperature.

Methodology

We have investigated the effect of seawater temperature on SSA particle size distribution and chemical composition in a controlled environment, and extended these findings to a global model to highlight the often-overlooked role of seawater surface temperature.

Key findings

• Elevated sea surface temperature increases the average SSA particle size, as shown by a decrease in the production of Aitken mode SSA and an increase in the production of accumulation and coarse mode SSA.
• Elevated sea surface temperature promotes significantly increased organic enrichment in SSA, and this promotion is more pronounced for more surface-active organics and SSA with smaller particle sizes.
• The decrease in Aitken mode SSA production and the increase in organic matter enrichment due to warmer sea surface temperature will inhibit the activation of these SSAs into cloud condensation nuclei, potentially affecting cloud formation in the marine boundary layer.
• The effect of sea surface temperature on organic enrichment in SSA will alter the global distribution of organic spray emissions via SSA.By combining the sea surface temperature, we estimate the organic spray emissions ranging from 23.45 to 55.78 Tg C yr^-1.

Conclusions and implications

From a microscopic mechanism perspective, sea surface temperature directly affects bubbles breakup, thereby altering the particle size distribution and chemical composition of SSA. Although we tried to quantify the effect, the deeper underlying mechanisms remain to be explored. From a macroscopic scale, sea surface temperature modulates the contribution of SSA particles of different sizes to cloud condensation nuclei, as well as the role of SSA in material transport at the air-sea interface. The impact of sea surface temperature on the formation and climate effect of SSA is greater than anticipated. Therefore, we recommend that future field studies, laboratory experiments, and model predictions fully account for the influence of sea surface temperature.