Characteristics in Atmospheric Chemistry between NO, NO2 and O-3 at an Urban Site during MAPS (Megacity Air Pollution Study)-Seoul, Korea

This study was conducted to understand roles of NOx (=NO+NO2) on high O-3 episodes at an urban monitoring station in Seoul. Concentrations of NO, NO2, NOy and O-3 were measured intensively at KIST monitoring station which located at urban center in Seoul metropolitan area during May 18 similar to June 13, 2015. Sampling period was planed because high O-3 and PM occurred frequently during from late spring to early summer months in Seoul. The experimental site locates in NW from center of Seoul and is surrounded by residential area. Belt highway of the city runs from north to west side nearby experimental site. Vehicle exhaust emissions due to heavy traffic influenced NOx concentration at the site during northwesterly wind. Specific NO2 concentration was measured by Blue Light photolytic converter, and it was compared to NO2 concentration measured by molybedenum converter. [NO2](phtolysis) was usually lower than [NO2](molybedenum) during the experiment period; however their diurnal variations were very similar. The linear relationship between these NO2 concentrations was found to be [NO2](phtolysis)=0.64 [NO2](molybedenum)-2.6, r(2)=0.83 during May 16 similar to 8, 2015. The difference between NO2 by molybdenum converter and by photolytic converter (Delta NO2=[NO2](molybedenum)-[NO2](phtolysis)) accounted for residual NOy which can represent NOz (=NOy-NOx). O-3 concentration showed typical daily trend which has maximum at late afternoon and minimum during the night. O-3 increased at a rate of 7 ppb/hr since 8 am. and reached the maximum concentration (similar to 80 ppb) at 3 pm.. The diurnal pattern of O-3 was inversely related with that of NO2, suggesting that the formation of O-3 was the result of photochemical activity of NO2.