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

초록

During the cold season in South Korea, NO3 3concentrations are known to significantly increase, often causing PM 2.5 to exceed air quality standards. This study investigated the formation mechanisms of NO3- 3in a suburban area with low anthropogenic emissions. The average PM 2.5 was 25.3 mu g m- 3 , with NO3- 3identified as the largest contributor. Ammonium-rich conditions prevailed throughout the study period, coupled with low atmospheric temperature facilitating the transfer of gaseous HNO3 3 into the particulate phase. This result indicates that the formation of HNO3 3 played a crucial role in determining particulate NO3 3concentration. Nocturnal increases in NO3- 3were observed alongside increasing ozone (O3) 3 ) and relative humidity (RH), emphasizing the significance of heterogeneous reactions involving N2O5. 2 O 5 . NO3 3concentrations 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 O3 3 and NO2, 2 , to produce NO3 3 radicals. High concentrations of Cl-and- and dust were also identified as contributors to the elevated NO3 3concentrations.

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