Meridional gradients of light absorbing carbon over northern Europe

In situ measurements have been made in the upper troposphere of the properties of particles containing light absorbing carbon ( LAC). These measurements, made in late November 2006 over northern Europe, show that the average LAC mass concentration varies between 1 and 5 ng m(-3) over a latitude range 50 degrees to 70 degrees N, with maxima at 50 degrees and 66 degrees. The relative fraction of all particles larger than 0.1 mu m that contain LAC decreases at higher latitudes. The derived extinction coefficient, which also increases with latitude, reaches a maximum of 1.4 Mm(-1) at 66 degrees. The air mass histories associated with the LAC were evaluated with back trajectory analysis using wind field analysis from the European Center for Median- Range Weather Forecast ( ECMWF). A positive correlation exists between the fraction of particles containing LAC and the maximum relative humidity ( RH), minimum temperature and maximum number of hours of cloud experienced by the air mass in the 5-10 days prior to being sampled by the aircraft. Air masses arriving from lower altitudes and with trajectories over North America also had larger concentration fractions of LAC. The average LAC mass is in good agreement with previous measurements made over North America for the same latitude range, and the span of values fits best with model predictions of LAC distributions that assume that the LAC transported from surface sources is hydrophobic.