It has been recently reported that the direct emission of nitrous acid (HONO) from soils can be a significant source of HONO especially during the day when a sufficient HONO source has not been found. In this study, the direct HONO emission from rice paddy soil was measured in the field during the mid-summer drainage period. To investigate the impact of fertilization, the system with a traditional amount of fertilization (the chemical nitrogen fertilizer system) and a non-fertilized system (the control system) were prepared. The maximum flux was 40.4 ng/m²/s which was observed after the soil oxidation reduction potential (Eh) had increased from negative values to positive values. The flux was higher during the daytime (3.5±0.9 ng/m²/s) than the nighttime (1.0±0.3 ng/m²/s). This cannot be explained only by the shift in the chemical equilibrium. The chemical nitrogen fertilizer system had a greater HONO flux than the control system on average. The reason could be that the chemical nitrogen fertilizer system has a lower soil moisture content. It was found that the direct emission amount from rice paddy soils may have a non-negligible impact on the atmospheric HONO concentrations.

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The relationship between NMHC, NO_x concentrations and Ox formation has been analyzed using the data observed during 1990–2011 in the Kanto region. The relationship seemed to be clearer by removing the effect of the meteorological conditions. It showed that the status of the Kanto region has been VOC-sensitive. The relationships between the precursor concentrations and Ox formation have varied according to the three periods showing the possibility that the change in the Ox measurement methods had been affected. The change in the VOC composition produced very little change in the reactivity although aromatic compounds had significantly decreased. According to the estimation using the occurrence ratios of high Ox concentration days, a 20% reduction of the NMHC concentration based on 2009–2011 average may cut in half the number of high Ox concentration days even if the NOx concentration decrease by 20%. The NMHC concentration should be reduced by 50% in order to reduce the number of high Ox concentration days to a zero level.

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In this study, the volatile organic compounds (VOCs) in evaporative gas from gasoline fuel were observed and the air quality evaluated during the refueling loss tests and the diurnal breathing loss (DBL) tests according to a gasoline fuel with a lower content of olefins compared to retail market fuels. The gasoline vapor compositions observed during the refueling loss tests were compared to the estimation calculated from the measured liquid gasoline composition using Raoult's law. As a result, there was no significant difference between the observations and the estimations of the gasoline vapor compositions according to refueling flows and environmental temperatures. During the DBL tests, the aromatics were predominant in the day 1 DBL, while the paraffins were predominant after the day 2 DBL. It is indicated that the permeation (the leakage of fuel from the fuel tank and tube) contributed to the day 1 results and the breakthrough (the overflow of fuel vapor from the carbon on the recovery equipment (canister)). To evaluate the air quality using the gasoline vapor composition data, the ozone formation potential (OFP) was performed using the maximum incremental reactivity (MIR) with the VOC data on the refueling loss and the DBL. It was indicated that the OFP of the gasoline fuel vapor in this study is similar to the OFP of the vapor from the refueling and breakthrough on the DBL. Furthermore, it is indicated that the olefin in the gasoline fuels can also effectively contribute to the OFP weighted emissions (OFP_EW) according to a comparison with the gasoline compositions in these test fuels and widely available fuels in Tokyo, and the values reported in a previous study. The OFP of the fuel vapors (e.g., refueling and breakthrough) and other emissions (e.g., biogenic VOC and stationary source) were estimated by the emission data from several prefectures. It indicated that the contribution of the refueling and breakthrough varied depending on the area. Furthermore, it was estimated that the OFP_EW of the fuel vapors contributed 4–21% of the total OFP_EW of the VOC emissions during August of 2010.

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We developed and released an atmospheric dispersion model, ADMER-PRO, which was applicable for secondary gaseous pollutants, such as ozone of high public concern, which was easy for non-modeling experts such as public administrators to use. The ADMER-PRO has the following features; 1) it can estimate the concentrations of both primary pollutants including any individual hazardous VOC components and secondary gaseous pollutants, 2) the ADMER-PRO can estimate easily the concentrations of multiple chemical species because it contains the necessary data, such as an emission inventory for some chemical species, 3) it can estimate long-term (e.g., annual) mean concentrations often necessary for chemical risk assessments, and 4) it can work on Windows PCs with simple operations. We used the ADMER-PRO to estimate the annual mean concentrations of multiple chemical species over the Kanto and Kinki areas, and tested the predictive performance of the model by comparing the calculated results with observations. The results showed that the ADMER-PRO can approximately reproduce observations of both primary pollutants, such as NO_x and individual hazardous VOC components, and secondary gaseous pollutants within a factor of two and the model has a comparatively good predictive performance. With the release of the ADMER-PRO, the chemical risk assessment and management considering both primary and secondary gaseous pollutants will be significantly enhanced.

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