Time Series Analysis of Climate and Air Pollution Factors Associated with Atmospheric Nitrogen Dioxide Concentration...

Nitrogen dioxide (NO₂) is an air pollutant discharged from combustion of human activities. Nitrous acid (HONO), measured as NO₂, is thought to impact respiratory function more than NO₂. HONO and NO₂ have an equilibrium relationship, and their reaction is affected by climate conditions. This study was conducted to discuss the extent of HONO contained in NO₂, depending on the level of urbanization. Whether climate conditions that promote HONO production enhanced the level of NO₂ measured was investigated using time series analysis. Climate and outdoor air pollution data measured in April 2009-March 2017 in urban (Tokyo, Osaka, and Aichi) and rural (Yamanashi) areas in Japan were used for the analysis. Air temperature had a trend of negative associations with NO₂, which might indicate the decomposition of HONO in the equilibrium between HONO and NO₂. The associations of relative humidity with NO₂ did not have consistent trends by prefecture: humidity only in Yamanashi was positively associated with NO₂. In high relative humidity conditions, the equilibrium goes towards HONO production, which was observed in Yamanashi, suggesting the proportion of HONO in NO₂ might be low/high in urban/rural areas.