The plots show the time-integrated concentration [deeper red reflecting high concentration] of an inert tracer emitted from RPB and advected backwards for 10 days. The tracer concentration is output over a vertical column of 0 – 2000 m agl. Contours in light red represent lower integrated concentrations (i.e. those regions contributed less to the air arriving at RPB) while the darker shading represent higher integrated concentrations (i.e. those regions contributed more to the air arriving at RPB).