Sable Island Station:

Atmospheric Aerosols 

(September 2003)

Aerosols are a suspension of solid or liquid particles in air.  They can alter Earth's climate by blocking the sun's radiation and by altering cloud properties, thus changing the hydrological cycle.  The ability of aerosols to modify climate depends in part on their chemical composition, size and number, their ability to grow into cloud droplets, and their ability to scatter and absorb solar radiation.   In polluted regions aerosols are also responsible for damaging health and reducing visibility.

Research on Sable Island to monitor the long range transport of pollution aerosols and to characterize their radiative properties, was carried out by the NOAA Climate Monitoring and Diagnostics Laboratory under John Ogren.  The program monitored aerosol chemical composition and number density, as well as the aerosol optical properties of scattering and absorption, from 1992 to 2000.   

Sable Island is ideally located to observe long range transport of pollution aerosols from the northeastern USA as well as background or natural sea salt aerosols in clean marine air masses from the Arctic.  Aerosols arriving at Sable Island varied seasonally.  Summertime weather is strongly influenced by high pressure systems over the eastern USA which circulate air from the northeastern USA to Atlantic Canada.  Aerosols during summer are relatively small and dark, comprised of mostly sulfate with small amounts of soot.  Figures 1 and 2 illustrate how the aerosol properties (as indicated by the scattering coefficient and absorption) changed as the origin of the air mass changed.   

Figure 1

Figure 2

On August 9th, winds were northeasterly and then southeasterly, bringing relatively clean air from regions having few pollution sources other than occasional ship traffic.  During this period, the aerosol concentrations were relatively low.  As wind speed increased later in the day, the concentration of coarse mode (large) aerosols increased - wind produced white caps and salt spray, thus generating large sea salt aerosols.  However, during this period the fine mode (small) aerosol scattering and absorption, both of which are indicative of pollution aerosols, remained low.   

On August 11th, the winds shifted to southwesterly, and as a high pressure system brought aerosols to Sable Island, there was a dramatic increase in both fine mode scattering (Figure 1) and aerosol absorption (Figure 2).  By August 13th, the wind had become northerly bringing clean marine air to the site.  Also, wind speed decreased, and the presence of large sea salt aerosols also decreased, as indicated by the drop in coarse mode aerosol scattering.   

Thanks to John Ogren and Anne Jefferson, NOAA.

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