On the characterization of nanoparticles emitted from combustion sources related to understanding their effects on health and climate

This work describes the use of well-controlled laboratory flames to produce aerosols of organic carbon (OC) as model particles representative of the OC fraction of combustion-generated particulate matter emissions in fresh exhausts. Water–particle interactions are explored in two specific cases. In the first case, particles are exposed to saturated environments and come into direct contact with liquid water by bubbling flame samples through a column of water. This case is representative of particle–liquid interactions relevant to wet removal routes by particle interception by rain or fog droplets or in biological systems covered with biological fluids composed mostly of water. In the second case, the particles are exposed to sub-saturated vapors with H2O concentrations representative of cloud-forming atmospheres. The particles' capacity to serve as atmospheric cloud condensation nuclei (CCN) by rapid growth to droplets was measured and compared to NaCl particles, which are highly soluble particles with well known activation diameters. The results show measureable interactions with water in highly saturated conditions. However, in sub-saturated environments, no growth by water condensation was observed, and fresh emissions of OC nanoparticles are not likely to act as CCN in atmospherically relevant humidity.