Cold air outbreak leads to new particle formation over the Eastern North Atlantic
Abstract
The indirect effects of aerosols on clouds remain highly uncertain in predicting the future climate. Among the major contributions to this uncertainty is poor understanding of the formation, evolution, and transport of aerosols in the remote marine environment, where the albedo and lifetime of low clouds are highly susceptible to perturbations in aerosol properties. Globally, new particle formation (NPF) represents an important source of aerosol and cloud condensation nuclei (CCN). Model simulations show that nearly half of the global CCN in the planetary boundary layer may be formed through NPF. However, the NPF in remote marine environment and its impact on CCN population are not well understood.
In this study, aerosol properties and meteorological conditions over the Eastern North Atlantic (ENA) are examined using both measurements onboard the US Department of Energy Gulfstream-1 (G-1) research aircraft during the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) campaign and long-term observation at the Atmospheric Radiation Measurement (ARM) ENA site on Graciosa Island. NPF was observed in lower free troposphere (FT) and upper decoupled layer within the marine boundary layer (MBL) following the passage of cold front, which is often associated with convective clouds and intense precipitation. The convective clouds transport ocean-emitted gas precursors upward to the upper decoupled layer and lower FT, and aerosol surface area concentrations are reduced due to wet deposition, leading to NPF. In addition, reduced temperature and relatively lower cloud fraction (i.e., stronger radiation and therefore photochemical activities) during the cold air outbreak following the cold front passage also facilitate NPF. In contrast, NPF in the surface mixed layer is unlikely, mainly due to a high aerosol surface area concentration (>20 μm2 cm-3) maintained by production of sea spray aerosols and/or reduced photochemical activity under overcast conditions. During the cold air outbreak, the newly formed particles in the upper decoupled layer are transported downwards into the surface mixed layer, where they grow and may become CCN. The influence of NPF during cold air outbreak on the population of MBL aerosols and CCN budget will be further discussed.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A13D..07W
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0320 Cloud physics and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCESDE: 4504 Air/sea interactions;
- OCEANOGRAPHY: PHYSICAL