Pan‐Arctic sunphotometry during the ARCTAS‐A campaign of April 2008

Aerosol optical depth (AOD) measurements were acquired at six Arctic sunphotometer sites during the ARCTAS‐A (April, 2008) campaign. Numerous smoke events were identified and related to extensive forest and agricultural fires in eastern Russia and northern Kazakhstan/ southwestern Russia respectively. An analysis of the fine (sub‐micron) optical depths from the six stations indicated the presence of underlying low frequency trends which were coherent with general meteorological considerations, source information, model estimates and remote sensing information. Low frequency (diurnal) coarse‐mode optical depth events were observed at a number of the stations; these singular events are likely due to ice particles whose nucleation may have been associated with the presence of smoke, or possibly dust.