Physical and chemical constraints on transformation and mass-increase of fine aerosols in northeast Asia

Over the past few decades, northeast Asia has suffered from the extreme levels of PM2.5 (particulate matter with an aerodynamic diameter smaller than 2.5 μm). Despite extensive efforts and the scientific advances in understanding PM2.5 pollution, the fundamental mechanisms responsible for the occurrence of high PM2.5 concentrations have not been comprehensively understood. In this study, we investigated the physical and chemical drivers for the formation and transformation of atmospheric particles using a four-year dataset of nanoparticle number size distributions, PM2.5 chemical composition, gaseous precursors, and meteorological variables in northeast Asia outflows. The empirical orthogonal function (EOF) analyses of size-separated particle numbers extracted two modes representing a burst of nanoparticles (EOF1) and an increase in PM2.5 mass (EOF2) associated with persistent anticyclone and synoptic-scale stagnation, respectively. The vertical structure of the particles demonstrated that the synoptic conditions also affected the daily evolution of boundary layer, promoting either the formation of nanoparticles through deep mixing or conversion into accumulation-mode particles in shallow mixed layers. In the haze-development episode equivalent to EOF2 during the KORUS-AQ (KORea-US Air Quality) campaign, the PM2.5 mass reached 63 μg m−3 with the highest contribution from inorganic constituents, which was accompanied by a thick coating of refractory black carbon (rBC) that linearly increased with condensation-mode particles. This observational evidence suggests that the thick coating of rBC resulted from an active conversion of condensable gases into particle-phase on the BC surface, thereby increasing the mass of the accumulation-mode aerosol. Consequently, this result complies with the strategy to reduce black carbon as a way to effectively mitigate haze pollution as well as climate change in northeast Asia.

Control Principle of Thermal Spray Process

In general, an essential target in the research and development of material process lies in how to establish the controlling principle on a designated material process. In this article, the current situation in the controlling of an ordinary thermal spray process, which is a representative of a thick coating formation process using particle deposition, is reviewed. Precise observation results were introduced to the ordinary thermal spray process. In the flattening behavior of the sprayed particle onto the substrate surface, critical conditions were recognized in both the substrate temperature and the ambient pressure. A transition temperature, Tt, and a transition pressure, Pt, were defined and introduced, respectively, for these critical conditions. Three-dimensional transition curvature, by combining both the Tt and the Pt dependence, was proposed as a control principle of the thermal spray process. Furthermore, particle melting in the ordinary thermal spray process has been recognized as a negative process. To overcome this problem, a new direction in coating technology development by using non-fusion solid particles has been tried recently, which is typically called the cold spray or the aerosol deposition process. As these processes have common characteristic for all, namely, a thick coating formation by the deposition of several micron-sized particles, the present state of the art, academic/technological issues, and the prospects for the future of these coating formation processes is comprehensively summarized in this article.