National Marine Science Centre, Southern Cross University, Coffs Harbour 2450, Australia.
School of Earth and Atmospheric Sciences, Queensland University of Technology, Brisbane 4000, Australia.
Environ Sci Technol. 2023 Dec 12;57(49):20559-20570. doi: 10.1021/acs.est.3c04793. Epub 2023 Nov 29.
Marine cloud brightening (MCB) is a potential intervention to mitigate the effects of climate change by increasing the reflectance of low-level maritime clouds, including those over the Great Barrier Reef. The technique involves dispersing a plume of submicrometer seawater droplets over the ocean, which evaporate, generating nanosized sea-salt aerosols (SSAs) that disperse through the atmosphere with some fraction incorporated into clouds. Droplet evaporation, which occurs in the immediate vicinity (meters to tens of meters) of the source, has been theorized to produce a negatively buoyant plume hindering the mixing of the sea-salt aerosol to cloud height and compromising the effectiveness of MCB. We characterized for the first time the nearfield aerosol dispersion from a point source of atomized seawater produced using the effervescent technique. We observed consistent vertical mixing of the plume up to 150 ± 5 m height at 1 km downwind. The extent of vertical dispersion was influenced by wind velocity and atmospheric stability. We found no evidence that negative buoyancy due to the evaporation of the 0.068 kg/s water fraction significantly suppressed vertical mixing. Our results can be attributed to the small droplet sizes generated by the effervescent spray technology and associated low flow rates required to generate around 10 droplets s. We estimate that, for a hypothetical implementation producing up to 10 s similarly sized SSAs, evaporative cooling is unlikely to significantly suppress the vertical dispersion of aerosol for MCB.
海洋云增亮（MCB）是一种通过增加低海拔海洋云（包括大堡礁上空的云）的反射率来减轻气候变化影响的潜在干预措施。该技术涉及在海洋上散布亚微米级海水液滴的羽流，这些液滴蒸发，产生纳米级海盐气溶胶（SSA），这些气溶胶在大气中分散，其中一部分被纳入云体。在源的附近（几米到几十米）发生的液滴蒸发，据推测会产生一个负浮力羽流，阻碍海盐气溶胶向云高的混合，并影响 MCB 的效果。我们首次对使用鼓泡技术产生的雾化海水点源的近场气溶胶扩散进行了表征。我们观察到，在 1 公里顺风处，羽流向上混合至 150±5 米的高度，混合程度受风速和大气稳定度的影响。我们没有发现由于 0.068kg/s 水部分的蒸发而产生的负浮力显著抑制垂直混合的证据。我们的结果可归因于鼓泡喷雾技术产生的小液滴尺寸以及产生约 10 个液滴/秒所需的低流速。我们估计，对于假设的实施，产生多达 10 个同样大小的 SSAs，蒸发冷却不太可能显著抑制 MCB 的气溶胶垂直扩散。
