This paper describes the gaseous organic carbon (OC) concentration in the PM_2.5 and positive artifact. The observations were done from April 2014 to March 2015 in Komae, Tokyo. In order to understand the influence of the gaseous OC, the measuring devices equipped with a denuder (denuder-filter method) and without a denuder (filter method) were simultaneously operated in parallel. The samples were analyzed for the OC concentrations by a thermal optical reflectance (TOR) method using a carbon analyzer manufactured by Sunset Laboratory. The average organic carbon concentrations were 2.8 μgC/m³ (filter method) and 1.7 μgC/m³ (denuder-filter method). The mean gaseous OC concentration was estimated to be 1.1 μgC/m³. It turned out that about 39% was the gaseous OC among the OC concentrations in the PM_2.5.

A number of automatic grid generators for numerical simulations has been developed in recent years. These utilities and CFD code using an unstructured grid enabled us to calculate the flow and dispersion over complex terrains with buildings. However, no reports are available regarding the large eddy simulations (LES) of contaminant dispersion using these utilities. This study was made to clarify the applicability of these grids to the simulation of flow and contaminant dispersion over a two-dimensional hill compared to the legacy orthogonal grids. We found that the characteristics of the separated flow were affected by the grid types near the terrain. Consequently, the contaminant dispersion was also strongly affected by the grid types due to the differences in the separated flow. We concluded that the grids near terrains should be parallel to the flow direction for the accurate predictions of contaminant dispersion.

This paper describes the development of an improved version of the High-Volume Impactor for PM_2.5 (HVI_2.5) for the sampling of ambient PM_2.5 aerosols, and improvement of its operation with an alternative impaction substrate. The improved-HVI_2.5 adopted a barb at the edge of the impaction plate to prevent the viscous liquid applied to the impaction substrates (e.g., fibrous filter-sheet) falling in drops onto the aerosol filter downstream resulting in the contamination of the collected aerosols. The size separation characteristics obtained for the improved-HVI_2.5 yielded 50% cut-off aerodynamic diameter Dp₅₀ of 2.5 μm at the flow rate of 520 L/min, with a steeper size selection curve than required by the Japanese Industrial Standards JIS Z8851:2008 and those of the Well Impactor Ninety-Six and Sharp-Cut Cyclone. As an alternative way to reduce the re-suspension of collected coarse particles from the impaction substrate without using a viscous liquid, the use of a hydrous gel-sheet was tested as an impaction substrate. The obtained Dp₅₀ and size selection curves were almost identical to those of the silicone-oil-impregnated glass-fiber filter. In addition, the uniformity of the collected substances on the aerosol filter was examined. Unlike SO₄^2- that is known to reside in fine mode size range, Ca²⁺, which consists of soil particle components, exhibited a non-uniform concentration distribution on the filter.