Reply on RC2

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> The Korea–United States Air Quality (KORUS-AQ) campaign is a joint study between the United States National Aeronautics and Space Administration (NASA) and the South Korea National Institute of Environmental Research (NIER) to monitor megacity and transboundary air pollution around the Korean Peninsula using airborne and ground-based measurements. Here, tropospheric nitrogen dioxide (NO<span class="inline-formula">₂</span>) slant column density (SCD) measurements were retrieved from Geostationary Trace and Aerosol Sensor Optimization (GeoTASO) L1B data during the KORUS-AQ campaign (2 May to 10 June 2016). The retrieved SCDs were converted to tropospheric vertical column densities using the air mass factor (AMF) obtained from a radiative transfer calculation with trace gas profiles and aerosol property inputs simulated with the Community Multiscale Air Quality (CMAQ) model and surface reflectance data obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS). For the first time, we examine highly resolved (250 m <span class="inline-formula">×</span> 250 m resolution) tropospheric NO<span class="inline-formula">₂</span> over the Seoul and Busan metropolitan regions and the industrial region of Anmyeon. We reveal that the maximum NO<span class="inline-formula">₂</span> vertical column densities (VCDs) were <span class="inline-formula">4.94×10¹⁶</span> and <span class="inline-formula">1.46×10¹⁷</span> molec. cm<span class="inline-formula">^−2</span> at 09:00 and 15:00 LT over Seoul, respectively, <span class="inline-formula">6.86×10¹⁶</span> and <span class="inline-formula">4.89×10¹⁶</span> molec. cm<span class="inline-formula">^−2</span> in the morning and afternoon over Busan, respectively, and <span class="inline-formula">1.64×10¹⁶</span> molec. cm<span class="inline-formula">^−2</span> over Anmyeon. The VCDs retrieved from the GeoTASO airborne instrument were correlated with those obtained from the Ozone Monitoring Instrument (OMI) (<span class="inline-formula"><i>r</i>=0.48</span>), NASA's Pandora Spectrometer System (<span class="inline-formula"><i>r</i>=0.91</span>), and NO<span class="inline-formula">₂</span> mixing ratios obtained from in situ measurements (<span class="inline-formula"><i>r</i>=0.07</span> in the morning, <span class="inline-formula"><i>r</i>=0.26</span> in the afternoon over the Seoul, and <span class="inline-formula"><i>r</i>&gt;0.56</span> over Busan). Based on our results, GeoTASO is useful for identifying NO<span class="inline-formula">₂</span> hotspots and their spatial distribution in highly populated cities and industrial areas.