Nitrate formation mechanisms causing high concentration of PM 2.5 in a residential city with low anthropogenic emissions during cold season

During the cold season in South Korea, NO concentrations are known to significantly increase, often causing PM to exceed air quality standards. This study investigated the formation mechanisms of NO in a suburban area with low anthropogenic emissions. The average PM was 25.3 μg m , with NO identified as the largest contributor. Ammonium-rich conditions prevailed throughout the study period, coupled with low atmospheric temperature facilitating the transfer of gaseous HNO into the particulate phase. This result indicates that the formation of HNO played a crucial role in determining particulate NO concentration. Nocturnal increases in NO were observed alongside increasing ozone (O ) and relative humidity (RH), emphasizing the significance of heterogeneous reactions involving N O . NO concentrations at the study site were notably higher than in Seoul, the upwind metropolitan area, during a high concentration episode. This difference could potentially attributed to lower local NO concentrations, which enhanced the reaction between O and NO , to produce NO radicals. High concentrations of Cl and dust were also identified as contributors to the elevated NO concentrations.