The ambient concentrations of individual VOC species were observed at five locations in Tokyo for two days in every season from autumn 2019 to summer 2020. The issues regarding air quality simulations and emission inventories were investigated by comparing the observed and simulated concentrations of the individual VOC species. Alkanes and ketones were the main contributors to the underestimated VOC concentrations found during all the seasons and all the locations. Underestimation of their hemispheric transport as well as domestic emissions were implied as the main factors because their reactivity in the atmosphere is low. When the reactivity in the atmosphere was considered, underestimation of the alkenes and overestimation of the aromatics were emphasized. The characteristics of the concentrations of individual species suggested underestimation of fugitive emissions from fuels and industrial solvents and overestimation of fugitive emissions from paint. The concentrations of biogenic VOC species were also largely underestimated, suggesting the importance of clarifying the biogenic VOC emissions and their seasonal variations in urban areas. Information about the concentrations about the individual VOC species are valuable to identify issues in air quality simulations and emission inventories as done in the present study.

In this study, we predicted the spatial distribution of PM_2.5 in the Kyushu area by a regression kriging (RK) model to evaluate how well a subset of the present networks can represent the full network. We developed a RK model with the particulate sulfate concentration in the PM_2.5 obtained by the chemical transport model as an indicator for regional pollution. The predictions were made for the daily average, annual average, and high concentration day average. The prediction performance was assessed by indicators calculated from the leave-one-out cross validation results. The R²-values were 0.90, 0.58, 0.70 and the RMSE-values were 2.47, 1.45, 2.40 µg/m³,respectively. The performance of the RK model in this study was comparable to that found in previous studies. The daily average prediction of the model showed a significantly better prediction accuracy than that of a RK model without the regional pollution indicator. These results suggested that the model in this study showed a good performance and was suitable for further evaluation. These results also suggested that the performance of the RK model might be improved by introducing explanatory variables according to features of the area, especially in areas with sparse observation networks.

From May 2016 to March 2021 in Sowa, Niigata pref., a parallel measurement was conducted between the traditional Open-faced Filter-Pack (OFP) and PM_2.5 Impactor-fitted Filter-Pack (IFP) methods to compare the influence of both chemical reactions and overestimation by particles and gas collected on filters, which are the so-called ‘artifacts’. Also, the degree of coincidence and data continuousness between the two methods was tested for contributing to potential long-term trend analyses. As for the particulate ions, the nss-SO₄²⁻ quantity (qty.) showed a high degree of coincidence between the two methods, while the coincidence of the Cl⁻ qty. highly depended on whether or not Cl⁻ of the Impactor adherent matter was included. Plus, the coincidence degree of the NO₃⁻ and NH₄⁺ qty. varied from season to season, and this seasonal fluctuation of the coincidence degree was almost opposite to that of each gas counterpart (HNO₃, NH₃), which supported the possibility that artifacts could occur during the OFP/IFP methods at different levels. Furthermore, particulate ingredients from sea salt and soil were collected on the Impactor surface, and the conc. of these ingredients showed correlations to the wind speeds, suggesting that artifacts by unintentionally collecting rain drops and ambient particles could occur during the OFP method under the strong wind conditions. The sum qty. of each ion and gas counterpart (HNO₃+NO₃⁻, NH₃+NH₄⁺, HCl+Cl⁻, SO₂+nss-SO₄²⁻) showed a high degree of coincidence between both methods, and the coincidence degree of HCl+Cl⁻ was remarkably higher when adding the Impactor adherent matter. Thus, with overestimation of the OFP method corrected, and using the sum qty. as the evaluation values, data continuousness between the two methods is likely to be retained.