Measurements of Cloud-Active Aerosol Particles in the Marine Boundary Layer from 80 °N to 85 °S during the Atmospheric Tomography (ATom) Mission
Abstract
Clouds in the remote marine lower troposphere are important components of the climate system. In this region, cloud condensation nuclei (CCN) are limited in abundance, and the radiative properties of low-altitude clouds are particularly sensitive to changes in CCN concentrations. CCN in the marine boundary layer (MBL) originate from primary processes such as bubble bursting and wind-driven spray, secondary processes such as the condensation of sulfur and organic species onto particles formed from gas-to-particle nucleation, and transport from continental sources.
We report results from airborne measurements of particle size distributions, volatility, and composition made from 80 °N to 85 °S over the central Pacific, Atlantic and Southern Oceans during the first three deployments of the airborne Atmospheric Tomography (ATom) mission. During ATom, nearly continuous en route profiles were made from 180 m to >12 km altitude using the instrumented NASA DC-8 aircraft. The resulting dataset provides 5-10 minute periods of measurements within the remote MBL, spaced every few degrees of latitude down the middle of the Pacific and Atlantic Oceans, in August 2016, February 2017, and October 2017. In these data a non-volatile primary sea-spray mode dominated aerosol mass. In contrast, secondary particles with diameters <0.4 μm, and often <0.1 μm, dominated the number concentration of CCN-sized particles. These particles were volatile at 300 °C and were composed primarily of sulfate species in most cases. Since new particle formation in the MBL is unlikely in most regions, these data suggest that particles formed in the free troposphere and entrained into the MBL dominate low-altitude remote CCN concentrations on a global scale. Improved understanding of the mechanisms of new particle formation in the upper free troposphere, growth of these particles during descent, and their entrainment into the MBL is needed to adequately simulate the concentrations of CCN in the MBL over large areas of the world's oceans. The global-scale ATom measurements, which are particularly valuable for particle sizes that are not detectable by satellite sensors, provide strong constraints on such simulations.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A51L2328B
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0322 Constituent sources and sinks;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0345 Pollution: urban and regional;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES