Figure 1

Principle of operation of the Picosecond Short-Range Elastic Backscatter Lidar (PSR-EBL) technique, intended to measure BC aerosol number and mass concentration, \(n_{\mathrm{o}}\) and \(m_{\mathrm{o}}\), respectively. A picosecond laser pulse is emitted from the lidar transmitter to illuminate a column of BC aerosols in the direction \(\hat{\mathbf {q}}^{\mathrm{inc}}\). When a pulse arrives at a particle (shown inset) at a range r, it may be partly absorbed and will scatter in all directions \(\hat{\mathbf {q}}\). The lidar return signal is directly related to the light backscattered by the particle to the receiver’s area A, which defines the received solid angle \(\Delta \Omega\). An example measurement of the return signal is shown at the bottom for a small-scale kerosene pool-fire at a range of 9 m from the instrument. Further description of the Colibri lidar is given in the Methods section.