Correlation of the ratio of non-methane hydrocarbon and nitrogen oxide concentrations in the atmosphere and outdoor environment

A correlation between atmospheric pollution due to the emission of volatile organic compounds (VOC) and the non-methane hydrocarbon/nitrogen oxide (NMHC/NO_x) ratio has been determined. We supposed the source of NMHC in a region using the NMHC/NO_x ratio without needing to consider diffusion and dilution due to meteorological conditions. At general measurement stations in Neyagawa and Higashiosaka cities in Osaka Prefecture, the NMHC/NO_x ratio was high in summer though the NMHC and NO_x concentrations were high in early winter. Conversely, measurements of the ratio at a traffic measurement station in Shijonawate did not have this pattern. That is, NMHC emission increased with the temperature in Neyagawa and Higashiosaka. It was concluded the waste plastic processing facility increased the NMHC/NO_x ratio by comparing the change in the annually averaged NMHC/NO_x ratio at Neyagawa and Higashiosaka with the developments of disposal and treatment facilities in Neyagawa. In the case of Neyagawa, ventilation is not suitable for improving indoor air quality, because the outdoor pollution level can be higher than that indoors. The NMHC/NO_x ratio is a useful index to evaluate the change in the regional environment due to VOC pollution, and it can judge whether outdoor air can improve indoor air quality by ventilation.