Aerosol properties and their influences on marine boundary layer cloud condensation nuclei at the ARM mobile facility over the Azores

Abstract

A multiplatform data set from the Clouds, Aerosol, and Precipitation in the Marine Boundary Layer (MBL) Graciosa, Azores, 2009-2010 field campaign was used to investigate how continental aerosols can influence MBL cloud condensation nuclei (CCN) number concentration (N CCN ). The seasonal variations of aerosol properties have shown that the winter and early spring months had the highest mean surface wind speed (> 5 m s À1) and greatest contribution of sea salt to aerosol optical depth (AOD), while continental fine mode aerosols were the main contributors to AOD during the warm season months (May-September). Five aerosol events consisting of mineral dust, pollution, biomass smoke, and volcanic ash particles were selected as case studies using Atmospheric Radiation Measurement (ARM) mobile facility measurements. The aerosols in Case I were found to primarily consist of coarse mode, Saharan mineral dust. For Case II, the aerosols were also coarse mode but consisted of volcanic ash. Case III had fine mode biomass smoke and pollution aerosol influences while Cases IV and V consisted of mixtures of North American pollution and Saharan dust that was advected by an extratropical cyclone to the Azores. Cases I, IV, and V exhibited weak correlations between aerosol loading and N CCN due to mineral dust influences, while Cases II and III had a strong relationship with N CCN likely due to the sulfate content in the volcanic ash and pollution particles. The permanent Eastern North Atlantic ARM facility over the Azores will aid in a future long-term study of aerosol effects on N CCN .

Clouds, Aerosols, and Precipitation in the Marine Boundary Layer: An Arm Mobile Facility Deployment

“…Despite this, when these particles are entrained into the PBL they grow because of aqueous phase deposition of sulfur species and they grow hygroscopically because of the high relative humidity in the boundary layer compared with the FT (Clarke et al 2013). Aerosol single scattering albedo measurements during CAP-MBL (not shown) indicate that aerosols are more absorbing during springtime, consistent with the idea that combustion aerosols from North America are potentially influential on the remote Atlantic during this season (Logan et al 2014). …”

Areal-Averaged Spectral Surface Albedo in an Atlantic Coastal Area: Estimation from Ground-Based Transmission

“…The first factor is related to the seasonal changes of wind speed. The mean surface wind speed approximately doubles from about 4 m/s (summer) to about 7 m/s (winter) at the AMF site [36]. The same is true for the maximum seasonal-averaged values of the surface wind speed: about 10 m/s (summer) to above 16 m/s (winter) [14].…”

“…The same is true for the maximum seasonal-averaged values of the surface wind speed: about 10 m/s (summer) to above 16 m/s (winter) [14]. The effect of the wind speed increase impacts the albedo in two ways: by expanding coverage of highly-reflective whitecaps [27] and by the increasing fraction of large particles (sea salt) in the atmosphere [36]. These two wind-dependent changes likely represent a challenge for the atmospheric correction process required for determination of the MODIS BRDFs [37].…”

Climatology Analysis of Aerosol Effect on Marine Water Cloud from Long-Term Satellite Climate Data Records

“…When aerosol concentration increases (or AOT increases) and the cloud base is coupled with the marine boundary layer, more aerosols will be transported into the cloud layer to become activated CCN and grow to cloud droplets with smaller CDER given fixed cloud liquid water content (or constant CWP) [76,77]. Then COD will increase according to Equation (1).…”