Long-Term Variation in the Tropospheric Nitrogen Dioxide Vertical Column Density over Korea and Japan from the MAX-DOAS Network, 2007–2017

Yongjoo Choi,Kihong Park,Yugo Kanaya,Hitoshi Irie,Jihyo Chong,Hisahiro Takashima

doi:10.3390/rs13101937

Yongjoo Choi, Kihong Park + Show 4 more

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We investigated long-term observations of the tropospheric nitrogen dioxide vertical column density (NO2 TropVCD) from the Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) network in Russia and ASia (MADRAS) from 2007 to 2017 at urban (Yokosuka and Gwangju) and remote (Fukue and Cape Hedo) sites in East Asia. The monthly mean in the NO2 TropVCD from MAX-DOAS measured at ~13:30 local time, which is the Ozone Monitoring Instrument (OMI) overpass time, shows good agreement with OMI data during summer, but differences between the two datasets increase in winter. The Theil-Sen slope of the long-term trend indicate a relatively rapid and gradual reduction in NO2 at Yokosuka and two remote sites (Fukue and Cape Hedo), respectively, regardless of the season except for fall at Fukue, but significant changes in NO2 are not observed at Gwangju, Korea. In contrast, OMI satellite data reveal an increase in the NO2 TropVCD at all sites except for Yokosuka, where a decreasing trend common to MAX-DOAS is found, suggesting that the results from satellites need to be cautiously used for investigating long-term trends in less polluted or remote areas. Using backward trajectories, potential source regions are identified for the two urban sites. The spatial distribution from OMI data shows good agreement with the potential source regions at Yokosuka. The potential source regions in Gwangju are identified as the National Industrial Complex in Yeosu and Gwangyang, while the transport route is not clearly visible with OMI data because of their low sensitivity in less polluted areas. The proposed approach is suitable for identifying potential source areas that might not be recognized by satellite observations.

Highlights

Nitrogen oxides (NOx; i.e., NO and NO2 ) are emitted from natural and anthropogenic sources [1,2] and play an important role in global air pollution by acting as catalysts of ozone (O3 ) formation in the troposphere and O3 destruction in the stratosphere [3]
Ozone Monitoring Instrument (OMI) NO2 TropVCD was selected from the grid (0.25◦ × 0.25◦ ) where each
Time-matched data (±30 min) with OMI overpass time of 13:30 local time (LT) and (2) daily mean using whole data because the photo-chemical reaction at 13:30 LT was active during the daytime

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Introduction

Nitrogen oxides (NOx; i.e., NO and NO2 ) are emitted from natural (biomass burning and lightning) and anthropogenic (fossil fuel combustion) sources [1,2] and play an important role in global air pollution by acting as catalysts of ozone (O3 ) formation in the troposphere and O3 destruction in the stratosphere [3]. The reaction cycle involving NO, NO2 , and O3 maintains an equilibrium state, the so-called photo-stationary state [4]. Peroxy radicals (HO2 and organic peroxy radicals, RO2 ), generated from the oxidation of volatile organic compounds (VOCs), react with NO to reproduce NO2 , and its photolysis generates O3 , effectively increasing the ozone concentration [5]. This reaction simultaneously recycles OH radicals, thereby maintaining

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