In-situ measurements of nighttime radical species (NO3 and N2O5) from Seoul N Tower in Korea during MAPS 2015

The importance of nitrate radical (NO3) chemistry has been emphasized in the nocturnal atmosphere which influences on the air quality in following day. This chemistry could gather its importance even more in urban setting or in downwind area of large urban emission sources. In support of these issue, efforts in investigating the nighttime chemical mechanisms has been made during MAPS 2015 (Megacity Air Pollution Study 2015) at Seoul in Korea from May 18th to June 12th of 2015. By deploying NOAA's state-of-the-art instrument, ARNOLD (Airborne Ring-down Nitrogen Oxide Laser Detector), high time resolution in-situ measurement of nitrate (NO3), dinitrogen pentoxide (N2O5) as well as other related trace gases species (e.g. NO, NO2, NOy, and O3) were made on the Seoul N Tower (inlet height: 362m ASL). The in-situ measurements of NO3 radical will provide good observational constraints on night time oxidation processes. The NO3 and N2O5 equilibrium and reactivity will be analyzed by comparison of their lifetimes to those calculated from VOC (Volatile Organic Compounds) measurements and kinetic calculations. Implications for nitrogen oxides species will be discussed.